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(Created page with "{{mergefrom|Niche adaptation|discuss=Talk:Niche_adaptation|date=July 2018}} {{About|the evolutionary process}} {{distinguish|Adoption|Acclimatization}} {{Evolutionary biology}...")
 
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{{mergefrom|Niche adaptation|discuss=Talk:Niche_adaptation|date=July 2018}}
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{{Use dmy dates|date=February 2015}}
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{{About|the evolutionary process}}
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{{chembox
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{{distinguish|Adoption|Acclimatization}}
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| Verifiedfields = changed
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{{Evolutionary biology}}
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| Watchedfields = changed
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In [[biology]], '''adaptation''' has three related meanings. Firstly, it is the dynamic evolutionary process that fits [[organism]]s to their environment, enhancing their [[Fitness (biology)|evolutionary fitness]]. Secondly, it is a state reached by the population during that process. Thirdly, it is a [[phenotypic trait|phenotypic]] or '''adaptive trait''', with a functional role in each individual organism, that is maintained and has been [[evolution|evolved]] by [[natural selection]].
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| verifiedrevid = 477003420
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| Name = Calcium carbonate
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| ImageFileL1 = calcium carbonate.png
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| ImageFileR1 = Calcium-carbonate-xtal-3D-SF.png
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| ImageFile2 = Calcium carbonate.jpg
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| IUPACName = Calcium carbonate
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| OtherNames = [[calcite]]; [[aragonite]]; [[chalk]]; [[Lime (material)]]; [[Limestone]]; [[marble]]; [[oyster]]; [[pearl]];
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|Section1={{Chembox Identifiers
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| UNII_Ref = {{fdacite|correct|FDA}}
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| UNII = H0G9379FGK
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| ChEMBL_Ref = {{ebicite|changed|EBI}}
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| ChEMBL = 1200539
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| KEGG_Ref = {{keggcite|correct|kegg}}
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| KEGG = D00932
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| InChI = 1/CH2O3.Ca/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
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| ChEBI_Ref = {{ebicite|correct|EBI}}
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| ChEBI = 3311
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| SMILES = [Ca+2].[O-]C([O-])=O
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| InChIKey = VTYYLEPIZMXCLO-NUQVWONBAS
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| SMILES1 = C(=O)([O-])[O-].[Ca+2]
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| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
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| StdInChI = 1S/CH2O3.Ca/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2
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| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
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| StdInChIKey = VTYYLEPIZMXCLO-UHFFFAOYSA-L
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| CASNo = 471-34-1
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| CASNo_Ref = {{cascite|correct|CAS}}
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| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
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| ChemSpiderID = 9708
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| EINECS = 207-439-9
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| PubChem = 10112
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| RTECS = FF9335000
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}}
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|Section2={{Chembox Properties
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| Formula = CaCO<sub>3</sub>
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| MolarMass = 100.0869 g/mol
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| Appearance = Fine white powder; chalky taste
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| Odor = odorless
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| Density = 2.711 g/cm<sup>3</sup> ([[calcite]])<br />2.83 g/cm<sup>3</sup> ([[aragonite]])
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| Solubility = 0.013 g/L (25 °C)<ref>{{cite book|title=SI Chemical Data Book (4th ed.) |publisher=John Wiley & Sons Australia, Ltd. |author1=Aylward, Gordon |author2=Findlay, Tristan |isbn=978-0-470-81638-7|year=2008}}</ref><ref>{{cite book|title=Calcium Carbonate: From the Cretaceous Period Into the 21st Century|publisher=Springer Science & Business Media|year=2001|url=https://books.google.com/books?id=pbkKGa19k5QC&pg=RA1-PR2|author=Rohleder, J. |author2=Kroker, E. |isbn=3-7643-6425-4}}</ref>
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| SolubilityProduct = 3.3{{e|-9}}<ref>{{cite book|last =Benjamin|first=Mark M.|year=2002|title=Water Chemistry |publisher=McGraw-Hill|isbn =0-07-238390-9|url=https://books.google.com/?id=67anQgAACAAJ}}</ref>
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| Solvent = dilute acids
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| SolubleOther = soluble
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| MeltingPt = 1,339 °C (2,442 °F; 1,612 K) (calcite) <br> 825 °C (1517 °F; 1,098 K) (aragonite) <ref>{{cite web|url=https://www.cdc.gov/niosh/docs/81-123/pdfs/0090.pdf|title=Occupational safety and health guideline for calcium carbonate|publisher=US Dept. of Health and Human Services|accessdate=31 March 2011}}</ref>
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| BoilingPt = decomposes
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| RefractIndex = 1.59
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| pKa = 9.0
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| pKb =
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| MagSus = -38.2·10<sup>−6</sup> cm<sup>3</sup>/mol
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}}
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|Section3={{Chembox Structure
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| CrystalStruct = Trigonal
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| SpaceGroup = <span style="text-decoration: overline">3</span>2/m
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}}
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|Section5={{Chembox Thermochemistry
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| DeltaHf = −1207&nbsp;kJ·mol<sup>−1</sup><ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 0-618-94690-X|page=A21}}</ref>
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| Entropy = 93&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup><ref name=b1 />
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}}
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|Section6={{Chembox Pharmacology
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| ATCCode_prefix = A02
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| ATCCode_suffix = AC01
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| ATC_Supplemental = {{ATC|A12|AA04}}
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}}
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|Section7={{Chembox Hazards
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| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1193.htm ICSC 1193]
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| MainHazards =
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| NFPA-H = 0
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| NFPA-F = 0
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| NFPA-R = 0
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| NFPA-S =
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| RPhrases =
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| SPhrases =
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| LD50 = 6450 mg/kg (oral, rat)
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| PEL = TWA 15 mg/m<sup>3</sup> (total) TWA 5 mg/m<sup>3</sup> (resp)<ref>{{PGCH|0090}}</ref>
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}}
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|Section8={{Chembox Related
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| OtherAnions = [[Calcium bicarbonate]]
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| OtherCations = [[Magnesium carbonate]]<br />[[Strontium carbonate]]<br />[[Barium carbonate]]
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| OtherCompounds = [[Calcium sulfate]]
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}}
 +
}}
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[[File:Calcite.png|thumb|right|Crystal structure of calcite]]
  
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Organisms face a succession of environmental challenges as they grow, and show adaptive [[Phenotypic plasticity|plasticity]] as traits [[ontogeny|develop]] in response to the imposed conditions. This gives them resilience to varying environments.
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'''Calcium carbonate''' is a [[chemical compound]] with the [[Chemical formula|formula]] [[Calcium|Ca]][[Carbon|C]][[Oxygen|O]]<sub>3</sub>. It is a common substance found in [[Rock (geology)|rocks]] as the [[mineral]]s [[calcite]] and [[aragonite]] (most notably as [[limestone]], which is a type of sedimentary rock build mainly of calcite) and is the main component of [[pearl]]s and the [[Seashell|shells of marine organisms]], [[snail]]s, and eggs. Calcium carbonate is the active ingredient in [[agricultural lime]] and is created when calcium ions in [[hard water]] react with [[carbonate ion]]s to create [[limescale]]. It is medicinally used as a [[calcium]] supplement or as an [[antacid]], but excessive consumption can be hazardous.
  
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==History ==
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==Chemistry==
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{{Main|History of evolutionary thought}}
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Calcium carbonate shares the typical properties of other carbonates. Notably,
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* it reacts with [[acid]]s, releasing [[carbon dioxide]]:
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:CaCO<sub>3</sub>(s) + 2H<sup>+</sup>(aq) → Ca<sup>2+</sup>(aq) + CO<sub>2</sub>(g) + H<sub>2</sub>O (l)
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* it releases carbon dioxide upon heating, called a [[thermal decomposition]] reaction, or [[calcination]] (to above 840&nbsp;°C in the case of CaCO<sub>3</sub>), to form [[calcium oxide]], commonly called [[quicklime]], with reaction [[enthalpy]] 178 kJ/mole:
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:CaCO<sub>3</sub> (s) → CaO (s) + CO<sub>2</sub> (g)
  
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Adaptation is an observable fact of life accepted by philosophers and natural historians from ancient times, independently of their views on [[evolution]], but their explanations differed. [[Empedocles]] did not believe that adaptation required a [[final cause]] (~ purpose), but thought that it "came about naturally, since such things survived." [[Aristotle]] did believe in final causes, but assumed that [[Aristotle's biology#Scale of being|species were fixed]].<ref>{{cite book |authorlink=Armand Marie Leroi |last=Leroi |first=Armand Marie |title=The Lagoon: How Aristotle Invented Science |titlelink=Aristotle's Lagoon |publisher=Bloomsbury |date=2015 |isbn=978-1408836224 |pages=91–92, 273, 288}}</ref>
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Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble [[calcium bicarbonate]].
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:CaCO<sub>3</sub> + CO<sub>2</sub> + H<sub>2</sub>O → Ca(HCO<sub>3</sub>)<sub>2</sub>
  
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[[File:Lamarck's Two-Factor Theory.svg|thumb|upright=1.7|The second of [[Jean-Baptiste Lamarck]]'s two factors (the first being a complexifying force) was an adaptive force that causes animals with a given [[body plan]] to adapt to circumstances by [[inheritance of acquired characteristics]], creating a diversity of [[species]] and [[genus|genera]].]]
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This reaction is important in the [[erosion]] of [[carbonate rock]], forming [[cavern]]s, and leads to [[hard water]] in many regions.
  
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In [[natural theology]], adaptation was interpreted as the work of a deity and as evidence for the existence of God.<ref>{{harvnb|Desmond|1989|pp=31–32, fn 18}}</ref> [[William Paley]] believed that organisms were perfectly adapted to the lives they led, an argument that shadowed [[Gottfried Wilhelm Leibniz]], who had argued that God had brought about "[[best of all possible worlds|the best of all possible worlds]]." [[Voltaire]]'s Dr. Pangloss<ref>{{cite book |author=Voltaire |title=Candide |publisher=Cramer et al |date=1759}}</ref> is a parody of this optimistic idea, and [[David Hume]] also argued against design.<ref>{{harvnb|Sober|1993|loc=chpt. 2}}</ref> The ''[[Natural theology#The Bridgewater Treatises|Bridgewater Treatises]]'' are a product of natural theology, though some of the authors managed to present their work in a fairly neutral manner. The series was lampooned by [[Robert Knox]], who held quasi-evolutionary views, as the ''Bilgewater Treatises''. [[Charles Darwin]] broke with the tradition by emphasising the flaws and limitations which occurred in the animal and plant worlds.<ref>{{harvnb|Darwin|1872|p=[http://darwin-online.org.uk/content/frameset?pageseq=425&itemID=F391&viewtype=side 397: "Rudimentary, Atrophied, and Aborted Organs"]}}</ref>
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An unusual form of calcium carbonate is the hexahydrate, [[ikaite]], CaCO<sub>3</sub>·6H<sub>2</sub>O. Ikaite is stable only below 6&nbsp;°C.
  
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[[Jean-Baptiste Lamarck]] proposed a tendency for organisms to become more complex, moving up a ladder of progress, plus "the influence of circumstances," usually expressed as ''use and disuse''.<ref>{{cite book |last1=Bowler |first1=Peter J. |title=Evolution The History of an Idea|date=1989 |publisher=University of California Press |isbn=0-520-06386-4 |page=86 |edition=Revised |origyear=1983}}</ref> This second, subsidiary element of his theory is what is now called [[Lamarckism]], a proto-evolutionary hypothesis of the [[inheritance of acquired characteristics]], intended to explain adaptations by natural means.<ref>See, for example, the discussion in {{harvnb|Bowler|2003|pp=86–95}}: "Whatever the true nature of Lamarck's theory, it was his mechanism of adaptation that caught the attention of later naturalists." (p. 90)</ref>
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==Preparation==
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The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually [[marble]]).
  
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Other natural historians, such as [[Georges-Louis Leclerc, Comte de Buffon|Buffon]], accepted adaptation, and some also accepted evolution, without voicing their opinions as to the mechanism. This illustrates the real merit of Darwin and [[Alfred Russel Wallace]], and secondary figures such as [[Henry Walter Bates]], for putting forward a mechanism whose significance had only been glimpsed previously. A century later, experimental field studies and breeding experiments by people such as [[E. B. Ford]] and [[Theodosius Dobzhansky]] produced [[Evidence of common descent|evidence that natural selection]] was not only the 'engine' behind adaptation, but was a much stronger force than had previously been thought.<ref name="Provine 1986">{{harvnb|Provine|1986}}</ref><ref>{{harvnb|Ford|1975}}</ref><ref name="Orr_2005">{{cite journal |last=Orr |first=H. Allen |authorlink=H. Allen Orr |date=February 2005 |title=The genetic theory of adaptation: a brief history |journal=[[Nature Reviews Genetics]] |volume=6 |issue=2 |pages=119–127 |doi=10.1038/nrg1523 |pmid=15716908}}</ref>
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Alternatively, calcium carbonate is prepared from [[calcium oxide]]. Water is added to give [[calcium hydroxide]] then [[carbon dioxide]] is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC):<ref name="PCC">{{cite web|title = Precipitated Calcium Carbonate |accessdate = 11 January 2014|url = http://www.lime.org/uses_of_lime/other_uses/precip_cc.asp}}</ref>
  
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==General principles ==
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: CaO + H<sub>2</sub>O → Ca(OH)<sub>2</sub>
 +
:<chem>Ca(OH)2 + CO2 -> CaCO3(v) + H2O</chem>
  
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{{Quotation|''The significance of an adaptation can only be understood in relation to the total biology of the species.''|[[Julian Huxley]]|''[[Evolution: The Modern Synthesis]]''<ref>{{harvnb|Huxley|1942|p=449}}</ref>}}
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==Structure==
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The thermodynamically stable form of CaCO<sub>3</sub> under normal conditions is hexagonal β-CaCO<sub>3</sub>, (the mineral [[calcite]]).<ref name ="Ropp">{{cite book|last=R C Ropp Elsevier|title=Encyclopedia of the alkaline earth compounds|publisher=Elsevier|isbn=9780444595508|pages=359–370}}</ref> Other forms can be prepared, the denser,(2.83 g/cc) orthorhombic λ-CaCO<sub>3</sub> ( the mineral [[aragonite]]) and μ-CaCO<sub>3</sub>, occurring as the mineral [[vaterite]].<ref name ="Ropp"/> The aragonite form can be prepared by precipitation at temperatures above 85&nbsp;°C, the vaterite form can be prepared by precipitation at 60&nbsp;°C.<ref name ="Ropp"/> Calcite contains calcium atoms coordinated by 6 oxygen atoms, in aragonite they are coordinated by 9 oxygen atoms.<ref name ="Ropp"/> The vaterite structure is not fully understood.<ref name="DemichelisRaiteri2013">{{cite journal|last1=Demichelis|first1=Raffaella|last2=Raiteri|first2=Paolo|last3=Gale|first3=Julian D.|last4=Dovesi|first4=Roberto|title=The Multiple Structures of Vaterite|journal=Crystal Growth & Design|volume=13|issue=6|year=2013|pages=2247–2251|issn=1528-7483|doi=10.1021/cg4002972}}</ref> Magnesium carbonate MgCO<sub>3</sub> has the calcite structure, whereas strontium and barium carbonate (SrCO<sub>3</sub> and BaCO<sub>3</sub>) adopt the aragonite structure, reflecting their larger ionic radii.<ref name ="Ropp"/>
  
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===What adaptation is===
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==Occurrence==
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Adaptation is primarily a process rather than a physical form or part of a body.<ref>{{harvnb|Mayr|1982|p=483}}: "Adaptation... could no longer be considered a static condition, a product of a creative past, and became instead a continuing dynamic process."</ref> An internal [[parasite]] (such as a [[liver fluke]]) can illustrate the distinction: such a parasite may have a very simple bodily structure, but nevertheless the organism is highly adapted to its specific environment. From this we see that adaptation is not just a matter of visible traits: in such parasites critical adaptations take place in the [[biological life cycle|life cycle]], which is often quite complex.<ref>{{harvnb |Price |1980}}</ref> However, as a practical term, "adaptation" often refers to a ''product'': those features of a [[species]] which result from the process. Many aspects of an animal or plant can be correctly called adaptations, though there are always some features whose function remains in doubt. By using the term ''adaptation'' for the evolutionary ''process'', and ''adaptive trait'' for the bodily part or function (the product), one may distinguish the two different senses of the word.<ref>{{cite encyclopedia |editor1-last=Daintith |editor1-first=John |editor2-last=Martin |editor2-first=Elizabeth A. |encyclopedia=A Dictionary of Science |title=adaptation |origyear=First published 1984 as ''Concise Science Dictionary'' |edition=6th |year=2010 |publisher=[[Oxford University Press]] |series=Oxford Paperback Reference |isbn=978-0-19-956146-9 |lccn=2010287468 |oclc=444383696 |page=13 |quote=Any change in the structure or functioning of successive generations of a population that makes it better suited to its environment.}}</ref><ref>{{harvnb |Bowler |2003 |p=10}}</ref><ref>{{harvnb |Patterson |1999 |p=1}}</ref><ref>{{harvnb |Williams |1966 |p=5}}: "Evolutionary adaptation is a phenomenon of pervasive importance in biology."</ref>
 
  
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Adaptation is one of the two main processes that explain the observed diversity of species, such as the different species of [[Darwin's finches]]. The other process is [[speciation]], in which new species arise, typically through [[reproductive isolation]].<ref>{{harvnb |Mayr |1963}}</ref><ref>{{harvnb |Mayr |1982 |pp=562–566}}</ref> A favourite example used today to study the interplay of adaptation and speciation is the evolution of [[cichlid]] [[fish]] in African lakes, where the question of reproductive isolation is complex.<ref name="Salzburger">{{cite journal |last1=Salzburger |first1=Walter |last2=Mack |first2=Tanja |last3=Verheyen |first3=Erik |last4=Meyer |first4=Axel |authorlink4=Axel Meyer |date=February 21, 2005 |title=Out of Tanganyika: Genesis, explosive speciation, key-innovations and phylogeography of the haplochromine cichlid fishes |url=http://www.biomedcentral.com/content/pdf/1471-2148-5-17.pdf |journal=[[BMC Evolutionary Biology]] |location=London |publisher=[[BioMed Central]] |volume=5 |number=17 |doi=10.1186/1471-2148-5-17 |pmc=554777 |pmid=15723698 |accessdate=2015-08-15}}</ref><ref name="Kornfield">{{cite journal |last1=Kornfield |first1=Irv |last2=Smith |first2=Peter F. |date=November 2000 |title=African Cichlid Fishes: Model Systems for Evolutionary Biology |journal=[[Annual Review of Ecology, Evolution, and Systematics |Annual Review of Ecology and Systematics]] |volume=31 |pages=163–196 |doi=10.1146/annurev.ecolsys.31.1.163}}</ref>
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[[File:Calcium carbonate chunks.JPG|thumb|Calcium carbonate chunks from clamshell]]
  
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Adaptation is not always a simple matter where the ideal phenotype evolves for a given external environment. An organism must be viable at all stages of its development and at all stages of its evolution. This places ''constraints'' on the evolution of development, behaviour, and structure of organisms. The main constraint, over which there has been much debate, is the requirement that each [[Genetics |genetic]] and phenotypic change during evolution should be relatively small, because developmental systems are so complex and interlinked. However, it is not clear what "relatively small" should mean, for example [[polyploid]]y in plants is a reasonably common large genetic change.<ref>{{harvnb|Stebbins|1950|loc=chs. 8 and 9}}</ref> The origin of [[eukaryote|eukaryotic]] [[endosymbiosis]] is a more dramatic example.<ref>{{harvnb|Margulis|Fester|1991}}</ref>
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===Geological sources===
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[[Calcite]], [[aragonite]] and [[vaterite]] are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include [[limestone]], [[chalk]], [[marble]] and [[travertine]].
  
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All adaptations help organisms survive in their [[ecological niche]]s.<ref>{{harvnb|Hutchinson|1965}}. The niche is the central concept in evolutionary ecology; see especially part II: "The niche: an abstractly inhabited hypervolume." (pp. 26–78)</ref> The adaptive traits may be structural, behavioural or [[Physiology|physiological]]. Structural adaptations are physical features of an organism, such as shape, body covering, armament, and [[comparative anatomy |internal organization]]. [[Ethology|Behavioural]] adaptations are inherited systems of behaviour, whether inherited in detail as [[instinct]]s, or as a [[neuropsychology|neuropsychological]] capacity for [[learning]]. Examples include [[Foraging |searching for food]], [[mating]], and [[Animal communication |vocalizations]]. Physiological adaptations permit the organism to perform special functions such as making [[venom]], secreting [[Snail slime |slime]], and [[phototropism]]), but also involve more general functions such as [[developmental biology |growth and development]], [[Thermoregulation |temperature regulation]], [[ions |ionic]] balance and other aspects of [[homeostasis]]. Adaptation affects all aspects of the life of an organism.
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[[File:Silfurberg.jpg|thumb|Calcite is the most stable polymorph of calcium carbonate. It is transparent to opaque. A transparent variety called [[Iceland spar]] (shown here) is used for optical purposes.{{clarify|date=January 2018}}]]
  
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The following definitions are given by the evolutionary biologist [[Theodosius Dobzhansky]]:
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===Biological sources===
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:1. ''Adaptation'' is the evolutionary process whereby an organism becomes better able to live in its [[habitat]] or habitats.<ref name="Dobzhansky T 1968">{{harvnb |Dobzhansky |1968 |pp=1–34}}</ref><ref>{{cite book |last1=Wang |first1=G |title=Analysis of Complex Diseases: A Mathematical Perspective |publisher=Taylor Francis |year=2014 |chapter=Chapter 5.6—Zero Order Adaptivity |pages=69 |isbn=9781466572232 |url={{Google books |plainurl=yes |id=DmDSBQAAQBAJ |page=69}}}}</ref><ref>{{cite book |title=Climate Change Impact on Livestock: Adaptation and Mitigation |publisher=Springer |editor1-last=Sejian |editor1-first=V. |editor2-last=Gaughan |editor2-first=J. |editor3-last=Baumgard |editor3-first=L. |editor4-last=Prasad |editor4-first=C. |year=2015 |pages=515 |isbn=9788132222651 |url={{Google books |plainurl=yes |id=D-G9BwAAQBAJ |page=515}}}}</ref>
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Eggshells, snail shells and most seashells are predominantly calcium carbonate and can be used as industrial sources of that chemical.<ref>{{cite web |title=How are seashells created? |author=Horne, Francis |date=23 October 2006 |work=Scientific American |accessdate=25 April 2012 |url=http://www.scientificamerican.com/article.cfm?id=how-are-seashells-created}}</ref> Oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source.<ref>{{cite web |url=http://www.webmd.com/drugs/drug-16642-Natural+Oyster+Shell+Calcium+Oral.aspx?drugid=16642&drugname=Natural+Oyster+Shell+Calcium+Oral| title=WebMD: Oyster shell calcium |publisher=WebMD| accessdate=25 April 2012}}</ref><ref>{{cite web |title=Oyster Shell Calcium Carbonate|publisher=Caltron Clays &amp Chemicals|url=http://caltronclays.in/Oyster_CC.html}}</ref> Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, however, they are not practical as an industrial source.<ref>{{cite journal|year=1993 |title=Absorbability of Calcium from Brassica Vegetables: Broccoli, Bok Choy, and Kale |journal=Journal of Food Science |volume=58 |issue=6 |pages=1378–1380|doi=10.1111/j.1365-2621.1993.tb06187.x|last1=Heaney|first1=R.P.|last2=Weaver|first2=C.M.|last3=Hinders|first3=SM.|last4=Martin|first4=B.|last5=Packard|first5=P.T.}}</ref>
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:2. ''Adaptedness'' is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats.<ref>{{harvnb |Dobzhansky |1970 |pp=4–6; 79–82}}</ref>
 
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:3. An ''adaptive trait'' is an aspect of the developmental pattern of the organism which enables or enhances the probability of that organism surviving and reproducing.<ref>{{cite journal |last=Dobzhansky |first=Theodosius |authorlink=Theodosius Dobzhansky |date=March 1956 |title=Genetics of Natural Populations. XXV. Genetic Changes in Populations of ''Drosophila pseudoobscura'' and ''Drosophila persimilis'' in Some Localities in California |journal=[[Evolution (journal) |Evolution]] |publisher=[[John Wiley & Sons]] for the [[Society for the Study of Evolution]] |volume=10 |issue=1 |pages=82–92 |doi=10.2307/2406099 |jstor=2406099}}</ref>
 
  
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===What adaptation is not===
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===Extraterrestrial===
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[[File:Tampering_W_Nature_Guacharacas.jpg|right|thumb|Some [[Generalist and specialist species|generalists]], such as [[bird]]s, have the flexibility to adapt to [[urban area]]s.]]
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Beyond Earth, strong evidence suggests the presence of calcium carbonate on [[Mars]]. Signs of calcium carbonate have been detected at more than one location (notably at [[Gusev crater|Gusev]] and [[Huygens (crater)|Huygens]] craters). This provides some evidence for the past presence of liquid water.<ref>{{cite journal
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| last1=Boynton |first1=WV
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| last2=Ming |first2=DW
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| last3=Kounaves |first3=SP
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| last4=Young |first4=SM
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| last5=Arvidson |first5=RE
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| last6=Hecht |first6=MH
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| last7=Hoffman |first7=J
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| last8=Niles |first8=PB
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| last9=Hamara |first9=DK
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| last10=Quinn
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| first10=R. C.
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| last11=Smith
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| first11=P. H.
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| last12=Sutter
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| first12=B
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| last13=Catling
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| first13=D. C.
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| last14=Morris
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| first14=R. V.
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| title=Evidence for Calcium Carbonate at the Mars Phoenix Landing Site
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| url=http://planetary.chem.tufts.edu/Boynton%20etal%20Science%202009v325p61.pdf
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| journal=Science |volume=325 |issue=5936 |pages= 61–64
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| year=2009 |pmid=19574384 |bibcode=2009Sci...325...61B
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| display-authors=3
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| doi=10.1126/science.1172768
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| doi-broken-date=2017-01-31
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}}</ref><ref name=Clark2007>
 +
{{cite journal
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| author1=Clark
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| year=2007
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| title=Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars
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| journal=[[Journal of Geophysical Research]]
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| volume=112 |pages=E06S01
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| doi=10.1029/2006JE002756
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| bibcode = 2007JGRE..112.6S01C
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| displayauthors=3
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| url=http://dspace.stir.ac.uk/bitstream/1893/17119/1/Clark2007_Evidence_for_montmorillonite_or_its_compositional_equivalent_in_Columbia_Hills_Mars.pdf
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}}</ref>
  
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Adaptation differs from flexibility, [[acclimatization]], and [[learning]]. Flexibility deals with the relative capacity of an organism to maintain itself in different habitats: its degree of [[Generalist and specialist species|specialization]]. Acclimatization describes automatic [[physiology|physiological]] adjustments during life;<ref name="Rymer2013">{{cite journal | last=Rymer | first=Tasmin | last2=Pillay | first2=Neville | last3=Schradin | first3=Carsten | title=Extinction or Survival? Behavioral Flexibility in Response to Environmental Change in the African Striped Mouse Rhabdomys | journal=Sustainability | volume=5 | issue=1 | date=2013 | doi=10.3390/su5010163 | pages=163–186}}</ref> learning means improvement in behavioral performance during life.<ref>{{cite book |last=Gross |first=Richard |title=Psychology: The Science of Mind and Behaviour |edition=6th  |url=https://books.google.com/books?id=Cle1Fcr_6_QC&pg=PT335 |year=2012 |publisher=Hodder |isbn=978-1-4441-6436-7 |page=335}}</ref> These terms are preferred to adaptation for changes during life which are not inherited by the next generation.
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==Geology==
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Carbonate is found frequently in geologic settings and constitutes an enormous [[carbon cycle|carbon reservoir]]. Calcium carbonate occurs as [[aragonite]], [[calcite]] and [[dolomite]]. The [[carbonate mineral]]s form the rock types: [[limestone]], [[chalk]], [[marble]], [[travertine]], [[tufa]], and others.
  
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Flexibility stems from [[phenotypic plasticity]], the ability of an organism with a given [[genotype]] to change its [[phenotype]] in response to changes in its [[habitat]], or to move to a different habitat.<ref>{{cite journal |last1=Price |first1=Trevor D. |last2=Qvarnström |first2=Anna |last3=Irwin |first3=Darren E. |date=July 2003 |title=The role of phenotypic plasticity in driving genetic evolution |journal=[[Proceedings of the Royal Society#Proceedings of the Royal Society B|Proceedings of the Royal Society B]] |volume=270 |issue=1523 |pages=1433–1440 |doi=10.1098/rspb.2003.2372 |pmc=1691402 |pmid=12965006}}</ref><ref>{{cite journal |last=Price |first=Trevor D. |date=June 2006 |title=Phenotypic plasticity, sexual selection and the evolution of colour patterns |journal=[[The Journal of Experimental Biology]] |volume=209 |issue=12 |pages=2368–2376 |doi=10.1242/jeb.02183 |pmid=16731813}}</ref> The degree of flexibility is inherited, and varies between individuals. A highly specialized animal or plant lives only in a well-defined habitat, eats a specific type of food, and cannot survive if its needs are not met. Many [[herbivore]]s are like this; extreme examples are [[koala]]s which depend on ''[[Eucalyptus]]'', and [[giant panda]]s which require [[bamboo]]. A generalist, on the other hand, eats a range of food, and can survive in many different conditions. Examples are humans, [[rat]]s, [[crab]]s and many carnivores. The ''tendency'' to behave in a specialized or exploratory manner is inherited—it is an adaptation. Rather different is developmental flexibility: "An animal or plant is developmentally flexible if when it is raised in or transferred to new conditions, it changes in structure so that it is better fitted to survive in the new environment," writes [[evolutionary biology|evolutionary biologist]] [[John Maynard Smith]].<ref>{{harvnb|Maynard Smith|1993|p=33}}</ref>
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In warm, clear tropical waters [[coral]]s are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including [[plankton]] (such as [[coccolith]]s and planktic [[foraminifera]]), [[coralline algae]], [[sea sponge|sponges]], [[brachiopod]]s, [[echinoderm]]s, [[bryozoa]] and [[Mollusc shell|mollusks]], are typically found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate. The [[calcification]] processes are changed by [[ocean acidification]].
  
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If humans move to a higher altitude, respiration and physical exertion become a problem, but after spending time in high altitude conditions they acclimatize to the reduced partial pressure of oxygen, such as by producing more [[red blood cell]]s. The ability to acclimatize is an adaptation, but the acclimatization itself is not. Fecundity goes down, but deaths from some tropical diseases also go down. Over a longer period of time, some people are better able to reproduce at high altitudes than others. They contribute more heavily to later generations, and gradually by natural selection the whole population becomes adapted to the new conditions. This has demonstrably occurred, as the observed performance of long-term communities at higher altitude is significantly better than the performance of new arrivals, even when the new arrivals have had time to acclimatize.<ref>{{cite journal |last1=Moore |first1=Lorna G. |last2=Regensteiner |first2=Judith G. |date=October 1983 |title=Adaptation to High Altitude |journal=[[Annual Review of Anthropology]] |volume=12 |pages=285–304 |doi=10.1146/annurev.an.12.100183.001441}}</ref>
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Where the [[oceanic crust]] is [[Subduction|subducted]] under a [[continental plate]] sediments will be carried down to warmer zones in the [[asthenosphere]] and [[lithosphere]]. Under these conditions calcium carbonate decomposes to produce [[carbon dioxide]] which, along with other gases, give rise to explosive [[volcano|volcanic eruptions]].
  
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===Adaptedness and fitness ===
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===Carbonate compensation depth===
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[[File:fitness-landscape-cartoon.png|thumb|In this sketch of a [[fitness landscape]], a population can evolve by following the arrows to the adaptive peak at point B, and the points A and C are local optima where a population could become trapped.]]
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The [[carbonate compensation depth]] (CCD) is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature drops and pressure increases. Calcium carbonate is unusual in that its solubility increases with decreasing temperature. Increasing pressure also increases the solubility of calcium carbonate. The carbonate compensation depth can range from 4–6&nbsp;km below sea level.
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{{Main|Fitness (biology)|Fitness landscape}}
 
  
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There is a relationship between adaptedness and the concept of fitness used in [[population genetics]]. Differences in fitness between [[genotype]]s predict the rate of evolution by natural selection. Natural selection changes the relative frequencies of alternative phenotypes, insofar as they are [[Heritability|heritable]].<ref name="Endler 33">{{harvnb|Endler|1986|pp=[https://books.google.com/books?id=MYk1XbelDssC&lpg=PA27&pg=PA33#v=onepage&q&f=false 33–51]}}</ref> However, a phenotype with high adaptedness may not have high fitness. Dobzhansky mentioned the example of the [[Sequoia sempervirens|Californian redwood]], which is highly adapted, but a [[Relict (biology)|relict]] species in danger of [[extinction]].<ref name="Dobzhansky T 1968" /> [[Elliott Sober]] commented that adaptation was a retrospective concept since it implied something about the history of a trait, whereas fitness predicts a trait's future.<ref name="Sober2">{{harvnb|Sober|1984|p=210}}</ref>
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===Role in taphonomy===
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Calcium carbonate can [[taphonomy|preserve fossils]] through [[permineralization]]. Most of the vertebrate fossils of the [[Two Medicine Formation]]—a [[geologic formation]] known for its [[duck-billed dinosaur]] eggs—are preserved by CaCO<sub>3</sub> permineralization.<ref name="twoturn" /> This type of preservation conserves high levels of detail, even down to the microscopic level. However, it also leaves specimens vulnerable to [[weathering]] when exposed to the surface.<ref name="twoturn">Trexler, D. (2001) [https://books.google.com/books?id=mgc6CS4EUPsC&pg=PA98 "Two Medicine Formation, Montana: geology and fauna"], pp. 298–309 in ''Mesozoic Vertebrate Life'', Tanke, D. H., and Carpenter, K. (eds), Indiana University Press. {{ISBN|0-253-33907-3}}</ref>
  
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:1. Relative fitness. The average contribution to the next generation by a genotype or a class of genotypes, relative to the contributions of other genotypes in the population.<ref name="Futuyma_Evolution">{{harvnb|Futuyma|1986|p=552}}</ref> This is also known as ''Darwinian fitness'', ''[[selection coefficient]]'', and other terms.
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[[Trilobite]] populations were once thought to have composed the majority of aquatic life during the [[Cambrian]], due to the fact that their calcium carbonate-rich shells were more easily preserved than those of other species,<ref>{{Cite book|url=https://www.nap.edu/catalog/11630/out-of-thin-air-dinosaurs-birds-and-earths-ancient-atmosphere|title=Out of Thin Air: Dinosaurs, Birds, and Earth's Ancient Atmosphere|last=Ward|first=Peter|date=|publisher=|year=|isbn=9780309666121|location=|pages=|language=en|doi=10.17226/11630}}</ref> which had purely chitinous shells.
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:2. Absolute fitness. The absolute contribution to the next generation by a genotype or a class of genotypes. Also known as the [[Malthusian growth model|Malthusian parameter]] when applied to the population as a whole.<ref name="Endler 33" /><ref>{{harvnb|Fisher|1930|p=25}}</ref>
 
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:3. Adaptedness. The extent to which a phenotype fits its local ecological niche. Researchers can sometimes test this through a [[Transplant experiment|reciprocal transplant]].<ref>{{cite journal | last=de Villemereuil | first=P. | last2=Gaggiotti | first2=O. E. | last3=Mouterde | first3=M. | last4=Till-Bottraud | first4=I | title=Common garden experiments in the genomic era: new perspectives and opportunities | journal=Heredity | volume=116 | issue=3 | date=2015-10-21 | doi=10.1038/hdy.2015.93 | pages=249–254| pmc=4806574 }}</ref>
 
  
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[[Sewall Wright]] proposed that populations occupy ''adaptive peaks'' on a fitness landscape. To evolve to another, higher peak, a population would first have to pass through a valley of maladaptive intermediate stages, and might be "trapped" on a peak that is not optimally adapted.<ref>{{harvnb|Wright|1932|pp=[http://www.esp.org/books/6th-congress/facsimile/contents/6th-cong-p356-wright.pdf 356–366]}}</ref>
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==Uses==
  
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===Genetic basis===
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===Industrial applications===
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A large diversity of genome [[DNA]]s in a species is the basis for adaptation and differentiation. A large population is needed to carry sufficient diversity. According to the misrepair-accumulation aging theory,<ref>{{cite arXiv |last1=Wang |first1=Jicun |last2=Michelitsch |first2=Thomas M. |last3=Wunderlin |first3=Arne |last4=Mahadeva |first4=Ravi |eprint=0904.0575 |title=Aging as a consequence of misrepair—A novel theory of aging |class=q-bio.TO |year=2009}}</ref><ref>{{cite arXiv |last1=Wang-Michelitsch |first1=Jicun |last2=Michelitsch |first2=Thomas M. |eprint=1503.07163 |title=Aging as a process of accumulation of misrepairs |class=q-bio.TO |year=2015}}</ref> The misrepair mechanism is important in maintaining a sufficient number of individuals in a species.<ref>{{cite arXiv |last1=Wang-Michelitsch |first1=Jicun |last2=Michelitsch |first2=Thomas M. |eprint=1505.03900 |title=Misrepair mechanism: a mechanism essential for individual adaptation, species adaptation and species evolution |class=q-bio.TO |year=2015}}</ref> misrepair is a way of repair for increasing the surviving chance of an organism when it has severe injuries. Without misrepairs, no individual could survive to reproduction age. Thus misrepair mechanism is an essential mechanism for the survival of a species and for maintaining the number of individuals. Although individuals die from aging, genome DNAs are being recopied and transmitted by individuals generation by generation. In addition, the DNA misrepairs in germ cells contribute also to the diversity of genome DNAs.
 
  
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==Types==
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The main use of calcium carbonate is in the construction industry, either as a building material or limestone aggregate for road building or as an ingredient of cement or as the starting material for the preparation of builder's lime by burning in a kiln. However, because of weathering mainly caused by [[acid rain]],<ref>{{cite web|title = Effects of Acid Rain|publisher = US Environmental Protection Agency|accessdate = 14 March 2015|url = http://www.epa.gov/acidrain/effects/materials.html}}</ref> calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw/primary substance for building materials.
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{{Quotation|''Adaptation is the heart and soul of evolution.''|[[Niles Eldredge]]|Reinventing Darwin: The Great Debate at the High Table of Evolutionary Theory<ref>{{harvnb|Eldredge|1995|p=33}}</ref>}}
 
  
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===Changes in habitat ===
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Calcium carbonate is also used in the purification of [[iron]] from [[iron ore]] in a [[blast furnace]]. The carbonate is calcined ''in situ'' to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron.<ref>{{cite web|title = Blast Furnace|publisher = Science Aid|accessdate = 30 December 2007|url = http://www.scienceaid.co.uk/chemistry/industrial/blastfurnace.html}}</ref>
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Before Darwin, adaptation was seen as a fixed relationship between an organism and its habitat. It was not appreciated that as the [[climate]] changed, so did the habitat; and as the habitat changed, so did the [[Biota (ecology)|biota]]. Also, habitats are subject to changes in their biota: for example, [[Invasive species|invasions]] of species from other areas. The relative numbers of species in a given habitat are always changing. Change is the rule, though much depends on the speed and degree of the change.
 
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When the habitat changes, three main things may happen to a resident population: habitat tracking, genetic change or extinction. In fact, all three things may occur in sequence. Of these three effects only genetic change brings about adaptation.
 
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When a habitat changes, the resident population typically moves to more suitable places; this is the typical response of flying [[insect]]s or oceanic organisms, which have wide (though not unlimited) opportunity for movement.<ref>{{harvnb|Eldredge|1985|p=136: "Of glaciers and beetles"}}</ref> This common response is called ''habitat tracking''. It is one explanation put forward for the periods of apparent stasis in the [[Fossil#Fossil record|fossil record]] (the [[punctuated equilibrium]] theory).<ref>{{harvnb|Eldredge|1995|p=64}}</ref>
 
  
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=== Genetic change ===
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In the [[oil industry]], calcium carbonate is added to [[drilling fluid]]s as a formation-bridging and filtercake-sealing agent; it is also a weighting material which increases the density of drilling fluids to control the downhole pressure. Calcium carbonate is added to swimming pools, as a [[pH]] corrector for maintaining [[alkalinity]] and offsetting the acidic properties of the disinfectant agent.{{citation needed|date=June 2015}}
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Genetic change occurs in a population when natural selection and [[mutation]]s act on its [[genetic variability]].<ref>{{cite encyclopedia |last=Hogan |first=C. Michael |editor-last=Monosson |editor-first=Emily |encyclopedia=[[Encyclopedia of Earth]] |title=Mutation |url=http://www.eoearth.org/view/article/159530/ |accessdate=2015-08-18 |date=October 12, 2010 |publisher=Environmental Information Coalition, [[National Council for Science and the Environment]] |oclc=72808636}}</ref> The first pathways of enzyme-based metabolism may have been parts of [[Purine metabolism|purine nucleotide metabolism]], with previous metabolic pathways being part of the ancient [[RNA world]]. By this means, the population adapts genetically to its circumstances.<ref name="Orr_2005" /> Genetic changes may result in visible structures, or may adjust physiological activity in a way that suits the habitat.
 
  
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Habitats and biota do frequently change. Therefore, it follows that the process of adaptation is never finally complete.<ref>{{harvnb|Mayr|1982|pp=481–483}}: This sequence tells how Darwin's ideas on adaptation developed as he came to appreciate it as "a continuing dynamic process."</ref> Over time, it may happen that the environment changes little, and the species comes to fit its surroundings better and better. On the other hand, it may happen that changes in the environment occur relatively rapidly, and then the species becomes less and less well adapted. Seen like this, adaptation is a genetic ''tracking process'', which goes on all the time to some extent, but especially when the population cannot or does not move to another, less hostile area. Given enough genetic change, as well as specific demographic conditions, an adaptation may be enough to bring a population back from the brink of [[extinction]] in a process called [[evolutionary rescue]]. It should be noted that adaptation does affect, to some extent, every species in a particular [[ecosystem]].<ref>{{harvnb|Sterelny|Griffiths|1999|p=217}}</ref><ref>{{harvnb|Freeman|Herron|2007|p=364}}</ref>
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It is also used as a raw material in the refining of sugar from [[sugar beet]]; It is calcined in a kiln with anthracite to produce calcium oxide and carbon dioxide. This burnt lime is then slaked in sweet water to produce a calcium hydroxide suspension for the precipitation of impurities in raw juice during [[carbonatation]].<ref>{{cite book|last1=McGinnis|first1=R.A.|title=Beet-Sugar Technology|publisher=Beet Sugar Development Foundation|page=178|edition=2nd}}</ref>
  
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[[Leigh Van Valen]] thought that even in a stable environment, competing species constantly had to adapt to maintain their relative standing. This became known as the [[Red Queen hypothesis]], as seen in host-[[parasite]] interaction.<ref>{{cite journal |doi=10.1126/sciadv.1501548 |last=Rabajante |first=J |title=Host-parasite Red Queen dynamics with phase-locked rare genotypes|journal=[[Science Advances]] |year=2016 |volume=2|pages=e1501548 |url=http://advances.sciencemag.org/content/2/3/e1501548 |display-authors=etal|bibcode=2016SciA....2E1548R}}</ref>
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Calcium carbonate has traditionally been a major component of blackboard chalk. However, modern manufactured chalk is mostly [[gypsum]], hydrated [[calcium sulfate]] CaSO<sub>4</sub>·2H<sub>2</sub>O. Calcium carbonate is a main source for growing [[Seacrete]], or [[Biorock]]. Precipitated calcium carbonate (PCC), pre-dispersed in slurry form, is a common filler material for latex gloves with the aim of achieving maximum saving in material and production costs.<ref name=precaco3>{{cite web|title=Precipitated Calcium Carbonate uses |url=http://www.aristocratholding.com/calris-5.html |deadurl=yes |archiveurl=https://web.archive.org/web/20140725032803/http://www.aristocratholding.com/calris-5.html |archivedate=25 July 2014 }}</ref>
  
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=== Co-adaptation ===
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Fine ground calcium carbonate (GCC) is an essential ingredient in the microporous film used in [[diapers]] and some building films as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. GCC or PCC is used as a filler in paper because they are cheaper than wood fiber. In terms of market volume, GCC are the most important types of fillers currently used.<ref>[http://www.ceresana.com/en/market-studies/additives/fillers/ Market Study Fillers, 2nd ed., published by Ceresana, September 2011]</ref> Printing and writing paper can contain 10–20% calcium carbonate. In North America, calcium carbonate has begun to replace [[Kaolinite|kaolin]] in the production of glossy paper. Europe has been practicing this as alkaline [[papermaking]] or acid-free papermaking for some decades. PCC used for paper filling and paper coatings is precipitated and prepared in a variety of shapes and sizes having characteristic narrow particle size distributions and equivalent spherical diameters of 0.4 to 3 micrometres.{{citation needed|date=June 2015}}
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{{main|Co-adaptation}}
 
  
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[[File:Plumpollen0060.jpg|thumb|Pollinating insects are co-adapted with flowering plants.]]
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Calcium carbonate is widely used as an extender in paints,<ref name = reade>{{cite web|title = Calcium Carbonate Powder|publisher = Reade Advanced Materials |date=4 February 2006|accessdate = 30 December 2007|url = http://www.reade.com/Products/Minerals_and_Ores/calcium_carbonate.html}}</ref> in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics.<ref name = reade/> Some typical examples include around 15 to 20% loading of chalk in [[Polyvinyl chloride|unplasticized polyvinyl chloride]] (uPVC) drain pipe, 5 to 15% loading of stearate coated chalk or marble in uPVC window profile. [[Polyvinyl chloride|PVC]] cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity).{{citation needed|date=June 2015}} [[Polypropylene]] compounds are often filled with calcium carbonate to increase rigidity, a requirement that becomes important at high use temperatures.<ref name= Imerys>{{cite web|url=http://www.imerys-perfmins.com/calcium-carbonate/eu/calcium-carbonate-plastic.htm |title=Calcium carbonate in plastic applications |accessdate=1 August 2008 |publisher=Imerys Performance Minerals}}</ref> Here the percentage is often 20–40%. It also routinely used as a filler in [[Thermosetting plastic|thermosetting resins]] (sheet and bulk molding compounds)<ref name = Imerys/> and has also been mixed with [[acrylonitrile butadiene styrene|ABS]], and other ingredients, to form some types of compression molded "clay" poker chips.{{citation needed|date=June 2015}} Precipitated calcium carbonate, made by dropping [[calcium oxide]] into water, is used by itself or with additives as a white paint, known as [[whitewashing]].{{citation needed|date=June 2015}}
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In [[coevolution]], where the existence of one species is tightly bound up with the life of another species, new or 'improved' adaptations which occur in one species are often followed by the appearance and spread of corresponding features in the other species. These [[co-adaptation]]al relationships are intrinsically dynamic, and may continue on a trajectory for millions of years, as has occurred in the relationship between [[flowering plant]]s and [[pollination|pollinating]] insects.<ref>{{cite book |title=Coevolution |author=[[Douglas J. Futuyma|Futuyma, D. J.]] and M. Slatkin (editors) |year=1983 |publisher=[[Sinauer Associates]] |isbn=0-87893-228-3 |pages=whole book}}</ref><ref>{{cite book |title=The Coevolutionary Process |author=Thompson, J. N.|year=1994 |publisher=University of Chicago Press |isbn=0-226-79759-7 |pages=whole book}}</ref>
 
  
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=== Mimicry ===
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Calcium carbonate is added to a wide range of trade and [[do it yourself]] adhesives, sealants, and decorating fillers.<ref name = reade/> Ceramic tile adhesives typically contain 70 to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting [[stained glass]] windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature.{{citation needed|date=June 2015}}
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{{main|Mimicry}}
 
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[[File:Wasp mimicry.jpg|thumb|right|A and B show real [[wasps]]; the rest are [[Batesian mimicry|Batesian mimics]]: three [[Hoverfly|hoverflies]] and one [[beetle]].]]
 
  
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Bates' work on Amazonian [[Butterfly|butterflies]] led him to develop the first scientific account of [[mimicry]], especially the kind of mimicry which bears his name: [[Batesian mimicry]].<ref>{{harvnb|Carpenter|Ford|1933}}</ref> This is the mimicry by a palatable species of an unpalatable or noxious species, gaining a selective advantage. A common example seen in temperate gardens is the [[hoverfly]], many of which—though bearing no sting—mimic the warning coloration of [[hymenoptera]] ([[wasp]]s and [[bee]]s). Such mimicry does not need to be perfect to improve the survival of the palatable species.<ref>{{harvnb|Wickler|1968}}</ref>
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In [[ceramics (art)|ceramics]]/glazing applications, calcium carbonate is known as ''whiting'',<ref name = reade/> and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a [[Ceramic flux|flux]] material in the glaze. Ground calcium carbonate is an [[abrasive]] (both as scouring powder and as an ingredient of household scouring creams), in particular in its calcite form, which has the relatively low hardness level of 3 on the [[Mohs scale of mineral hardness]], and will therefore not scratch [[glass]] and most other [[ceramic]]s, [[Vitreous enamel|enamel]], [[bronze]], [[iron]], and [[steel]], and have a moderate effect on softer metals like [[aluminium]] and [[copper]]. A paste made from calcium carbonate and [[deionized water]] can be used to clean [[tarnish]] on [[silver]].<ref name="Make it Shine">{{cite web|title = Ohio Historical Society Blog: Make It Shine|publisher = Ohio Historical Society |url = http://ohiohistory.wordpress.com/2011/06/02/making-it-shine/}}</ref>
  
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Bates, Wallace and [[Fritz Müller]] believed that Batesian and [[Müllerian mimicry]] provided [[coloration evidence for natural selection|evidence for the action of natural selection]], a view which is now standard amongst biologists.<ref>{{harvnb|Moon|1976}}</ref><ref>{{harvnb|Ruxton|Sherratt|Speed|2004}}</ref><ref>{{cite journal |last=Mallet |first=James |authorlink=James Mallet |date=November 2001 |title=The speciation revolution |url=http://www.ucl.ac.uk/taxome/jim/pap/malletjeb01.pdf |journal=[[Journal of Evolutionary Biology]] |volume=14 |issue=6 |pages=887–888 |doi=10.1046/j.1420-9101.2001.00342.x}}</ref>
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===Health and dietary applications===
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[[File:500 mg calcium supplements with vitamin D.jpg|thumb|500-milligram calcium supplements made from calcium carbonate]]
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Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement for [[antacid|gastric antacid]]<ref name = medline>{{cite web|work = Medline Plus|publisher = [[National Institutes of Health]]|title = Calcium Carbonate |date=1 October 2005|accessdate = 30 December 2007|url = https://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a601032.html |archiveurl = https://web.archive.org/web/20071017031324/http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a601032.html <!-- Bot retrieved archive --> |archivedate = 17 October 2007}}</ref> (e.g., [[Tums]]). It may be used as a [[phosphate binder]] for the treatment of [[hyperphosphatemia]] (primarily in patients with [[chronic renal failure]]). It is also used in the pharmaceutical industry as an inert [[Excipient|filler]] for [[Tablet (pharmacy)|tablets]] and other [[pharmaceuticals]].<ref>{{cite book|author1=Lieberman, Herbert A. |author2=Lachman, Leon |author3=Schwartz, Joseph B. |title = Pharmaceutical Dosage Forms: Tablets|year = 1990|isbn = 0-8247-8044-2|page=153|publisher = Dekker|location = New York}}</ref>
  
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=== Trade-offs ===
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Calcium carbonate is used in the production of calcium oxide as well as toothpaste and has seen a resurgence as a food preservative and color retainer, when used in or with products such as organic apples.<ref>[http://chemistry.about.com/od/foodcookingchemistry/a/cadditives.htm Food Additives – Names Starting with C]. Chemistry.about.com (10 April 2012). Retrieved 2012-05-24.</ref>
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{{Quotation|''It is a profound truth that Nature does not know best; that genetical evolution... is a story of waste, makeshift, compromise and blunder.''|[[Peter Medawar]]|The Future of Man<ref>{{harvnb|Medawar|1960}}</ref>}}
 
  
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All adaptations have a downside: [[horse]] legs are great for running on grass, but they can't scratch their backs; [[mammal]]s' hair helps temperature, but offers a niche for [[Parasitism#Types|ectoparasites]]; the only flying [[penguin]]s do is under water. Adaptations serving different functions may be mutually destructive. Compromise and makeshift occur widely, not perfection. Selection pressures pull in different directions, and the adaptation that results is some kind of compromise.<ref>{{cite journal |last=Jacob |first=François |authorlink=François Jacob |date=June 10, 1977 |title=Evolution and Tinkering |journal=[[Science (journal)|Science]] |publisher=[[American Association for the Advancement of Science]] |volume=196 |issue=4295 |pages=1161–1166 |doi=10.1126/science.860134 |pmid=860134|bibcode=1977Sci...196.1161J }}</ref>
+
Excess calcium from supplements, fortified food and high-calcium diets, can cause [[milk-alkali syndrome]], which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in [[renal failure]], [[alkalosis]], and [[hypercalcaemia]], mostly in men with peptic ulcer disease. These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting. Milk-alkali syndrome declined in men after effective treatments for [[peptic ulcer]] disease arose. During the past 15 years, it has been reported in women taking calcium supplements above the recommended range of 1.2 to 1.5&nbsp;g daily, for prevention and treatment of osteoporosis, and is exacerbated by [[dehydration]]. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. Excessive calcium intake can lead to [[hypercalcemia]], complications of which include vomiting, abdominal pain and altered mental status.<ref>{{cite journal|title=Clinical problem-solving, back to basics|author=Gabriely, Ilan |journal=New England Journal of Medicine|year=2008|volume=358|pmid=18450607|doi=10.1056/NEJMcps0706188|issue=18|last2=Leu|first2=James P.|last3=Barzel|first3=Uriel S.|pages=1952–6}}</ref>
  
−
{{Quotation|''Since the phenotype as a whole is the target of selection, it is impossible to improve simultaneously all aspects of the phenotype to the same degree.''|[[Ernst Mayr]]|[[The Growth of Biological Thought|The Growth of Biological Thought: Diversity, Evolution, and Inheritance]]<ref>{{harvnb|Mayr|1982|p=589}}</ref>}}
+
As a [[food additive]] it is designated E170,<ref>{{cite web|title=Food-Info.net : E-numbers : E170 Calcium carbonate|url=http://www.food-info.net/uk/e/e170.htm}} 080419 food-info.net</ref> and it has an INS number of 170. Used as an acidity regulator, anticaking agent, stabiliser or colour it is approved for usage in the EU,<ref>UK Food Standards Agency: {{cite web |url=http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist |title=Current EU approved additives and their E Numbers |accessdate=27 October 2011}}</ref> USA<ref>US [[Food and Drug Administration]]: {{cite web|url=http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/FoodAdditiveListings/ucm091048.htm |title=Listing of Food Additives Status Part I |accessdate=27 October 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20130314104055/http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/FoodAdditiveListings/ucm091048.htm |archivedate=14 March 2013 |df=dmy }}</ref> and [[Australia]] and [[New Zealand]].<ref>Australia New Zealand Food Standards Code{{cite web |url=http://www.comlaw.gov.au/Details/F2011C00827 |title=Standard 1.2.4 – Labelling of ingredients |accessdate=27 October 2011}}</ref> It is used in some [[soy milk]] and [[almond milk]] products as a source of dietary calcium; one study suggests that calcium carbonate might be as [[bioavailable]] as the calcium in cow's milk.<ref>{{Cite journal
 +
| pmid = 16177199
 +
| year = 2005
 +
| author1 = Zhao
 +
| first1 = Y
 +
| title = Calcium bioavailability of calcium carbonate fortified soymilk is equivalent to cow's milk in young women
 +
| journal = The Journal of Nutrition
 +
| volume = 135
 +
| issue = 10
 +
| pages = 2379–82
 +
| last2 = Martin
 +
| first2 = B. R.
 +
| last3 = Weaver
 +
| first3 = C. M.
 +
}}</ref> Calcium carbonate is also used as a [[firming agent]] in many canned or bottled vegetable products.
  
−
Consider the antlers of the [[Irish elk]], (often supposed to be far too large; in [[deer]] antler size has an [[Allometry|allometric]] relationship to body size). Obviously, antlers serve positively for defence against [[Predation|predator]]s, and to score victories in the annual [[rut (mammalian reproduction)|rut]]. But they are costly in terms of resource. Their size during the [[last glacial period]] presumably depended on the relative gain and loss of reproductive capacity in the population of elks during that time.<ref>{{cite journal |last=Gould |first=Stephen Jay |authorlink=Stephen Jay Gould |date=June 1974 |title =The Origin and Function of 'Bizarre' Structures: Antler Size and Skull Size in the 'Irish Elk,' ''Megaloceros giganteus'' |journal=Evolution |volume=28 |issue=2 |pages=191–220 |doi=10.2307/2407322 |jstor=2407322}}</ref> As another example, [[camouflage]] to avoid detection is destroyed when vivid [[animal coloration|coloration]] is displayed at mating time. Here the risk to life is counterbalanced by the necessity for reproduction.<ref name="Garcia2013">{{cite journal | last=Garcia | first=J. E. | last2=Rohr | first2=D. | last3=Dyer | first3=A. G. | title=Trade-off between camouflage and sexual dimorphism revealed by UV digital imaging: the case of Australian Mallee dragons (Ctenophorus fordi) | journal=Journal of Experimental Biology | volume=216 | issue=22 | date=2013 | doi=10.1242/jeb.094045 | pages=4290–4298}}</ref>
+
===Agricultural use===
 +
[[Agricultural lime]], powdered chalk or limestone, is used as a cheap method for neutralising acidic soil, making it suitable for planting.<ref name="Oates2008">{{cite book|first=J. A. H.|last=Oates|title=Lime and Limestone: Chemistry and Technology, Production and Uses|url=https://books.google.com/books?id=MVoEMNI5Vb0C&pg=PA111|date=11 July 2008|publisher=John Wiley & Sons|isbn=978-3-527-61201-7|pages=111–3}}</ref>
  
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Stream-dwelling salamanders, such as [[Caucasian salamander]] or [[Gold-striped salamander]] have very slender, long bodies, perfectly adapted to life at the banks of fast small rivers and mountain [[Stream|brook]]s. Elongated body protects their [[larva]]e from being washed out by current. However, elongated body increases risk of desiccation and decreases dispersal ability of the salamanders; it also negatively affects their [[fecundity]]. As a result, [[fire salamander]], less perfectly adapted to the mountain brook habitats, is in general more successful, have a higher fecundity and broader geographic range.<ref>{{cite journal |last=Tarkhnishvili |first=David N. |year=1994 |title=Interdependences between Populational, Developmental and Morphological Features of the Caucasian salamander, ''Mertensiella caucasica'' |url=http://eprints.iliauni.edu.ge/usr/share/eprints3/data/814/1/Caucasian%20Salamander%20Ecological%20Constraints.pdf |journal=Mertensiella  |volume=4 |pages=315–325 |accessdate=2015-08-18}}</ref>
+
===Household use===
 +
Calcium carbonate is a key ingredient in many household cleaning powders like [[Comet (cleanser)]] and is used as a scrubbing agent.
  
−
[[File:Pfau imponierend.jpg|thumb|left|An [[Indian peafowl|Indian peacock]]'s train<br />in full display]]
+
===Environmental applications===
  
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The [[Peafowl|peacock]]'s ornamental train (grown anew in time for each mating season) is a famous adaptation. It must reduce his maneuverability and flight, and is hugely conspicuous; also, its growth costs food resources. Darwin's explanation of its advantage was in terms of [[sexual selection]]: "This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction."<ref>{{harvnb|Darwin|1871|p=[http://darwin-online.org.uk/content/frameset?pageseq=269&itemID=F937.1&viewtype=side 256]}}</ref> The kind of sexual selection represented by the peacock is called 'mate choice,' with an implication that the process selects the more fit over the less fit, and so has survival value.<ref>The case was treated by {{harvnb|Fisher|1930|pp=134–139}}</ref> The recognition of sexual selection was for a long time in abeyance, but has been rehabilitated.<ref>{{harvnb|Cronin|1991}}</ref>
+
In 1989, a researcher, Ken Simmons, introduced CaCO<sub>3</sub> into the Whetstone Brook in [[Massachusetts]].<ref>{{cite news|agency = [[Associated Press]]|title =
 +
Limestone Dispenser Fights Acid Rain in Stream |date=13 June 1989|url = https://query.nytimes.com/gst/fullpage.html?res=950DEFD9173FF930A25755C0A96F948260|work = The New York Times}}</ref> His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amount of aluminium ions in the area of the brook that was not treated with the limestone. This shows that CaCO<sub>3</sub> can be added to neutralize the effects of acid rain in [[river]] ecosystems. Currently calcium carbonate is used to neutralize acidic conditions in both soil and water.<ref name=env>{{cite web|title=Environmental Uses for Calcium Carbonate|url=http://www.congcal.com/markets/environmental/|publisher=Congcal|accessdate=5 August 2013}}</ref><ref>{{cite journal|author = Schreiber, R. K. |title = Cooperative federal-state liming research on surface waters impacted by acidic deposition|year = 1988|journal =Water, Air, & Soil Pollution|volume = 41|issue = 1|pages = 53–73|doi=10.1007/BF00160344|url=https://link.springer.com/article/10.1007%2FBF00160344|doi-broken-date = 2017-01-31}}</ref><ref>{{cite web|title = Effects of low pH and high aluminum on Atlantic salmon smolts in Eastern Maine and liming project feasibility analysis|year = 2006|author1=Kircheis, Dan |author2=Dill, Richard |publisher = National Marine Fisheries Service and Maine Atlantic Salmon Commission|url = http://www.mainesalmonrivers.org/pages/Liming%20Project%20Rpt.pdf|format = reprinted at Downeast Salmon Federation}}</ref> Since the 1970s, such ''liming'' has been practiced on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly.<ref>{{Cite journal |doi= 10.1007/s10933-006-9014-9 |title= Liming placed in a long-term perspective: A paleolimnological study of 12 lakes in the Swedish liming program |journal= Journal of Paleolimnology |volume= 37 |issue= 2 |pages= 247–258 |year= 2006 |last1= Guhrén |first1= M. |last2= Bigler |first2= C. |last3= Renberg |first3= I. |bibcode= 2007JPall..37..247G }}</ref>
  
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The conflict between the size of the human [[Fetus|foetal]] brain at birth, (which cannot be larger than about 400&nbsp;cm<sup>3</sup>, else it will not get through the mother's [[pelvis]]) and the size needed for an adult brain (about 1400&nbsp;cm<sup>3</sup>), means the brain of a newborn child is quite immature. The most vital things in human life (locomotion, speech) just have to wait while the brain grows and matures. That is the result of the birth compromise. Much of the problem comes from our upright [[Bipedalism|bipedal]] stance, without which our pelvis could be shaped more suitably for birth. [[Neanderthal]]s had a similar problem.<ref>{{cite journal |last=Rosenberg |first=Karen R. |year=1992 |title=The evolution of modern human childbirth |journal=American Journal of Physical Anthropology |location=Hoboken, NJ |publisher=John Wiley & Sons for the [[American Association of Physical Anthropologists]] |volume=35 |issue=Supplement S15 |pages=89–124 |doi=10.1002/ajpa.1330350605}}</ref><ref>{{cite journal |last1=Friedlander |first1=Nancy J. |last2=Jordan |first2=David K. |authorlink2=David K. Jordan |date=October–December 1994 |title=Obstetric implications of Neanderthal robusticity and bone density |journal=Human Evolution  |volume=9 |issue=4 |pages=331–342 |doi=10.1007/BF02435519}}</ref><ref>{{harvnb|Miller|2007}}</ref>
+
Calcium carbonate is also used in [[flue gas desulfurisation]] applications eliminating harmful SO<sub>2</sub> and NO<sub>2</sub> emissions from coal and other fossil fuels burnt in large fossil fuel power stations.<ref name=env/>
  
−
As another example, the long neck of a [[giraffe]] is a burden and a blessing. The neck of a giraffe can be up to {{convert|2|m|abbr=on}} in length.<ref>{{harvnb|Williams|2010|p=29}}</ref> This neck can be used for inter-species competition or for foraging on tall trees where shorter [[herbivore]]s cannot reach. However, as previously stated, there is always a trade-off. This long neck is heavy and it adds to the body mass of a giraffe, so the giraffe needs an abundance of nutrition to provide for this costly adaptation.<ref>{{cite journal |last1=Altwegg |first1=Robert E. |last2=Simmons |first2=Res |title=Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe |date=September 2010 |journal=[[Journal of Zoology]] |volume=282 |issue=1 |pages=6–12 |doi=10.1111/j.1469-7998.2010.00711.x}}</ref>
+
==Calcination equilibrium==
 +
[[Calcination]] of [[limestone]] using [[charcoal]] fires to produce [[calcium oxide|quicklime]] has been practiced since antiquity by cultures all over the world. The temperature at which limestone yields calcium oxide is usually given as 825&nbsp;°C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and [[carbon dioxide]] at any temperature. At each temperature there is a [[partial pressure]] of carbon dioxide that is in equilibrium with calcium carbonate. At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO<sub>2</sub> pressure is only a tiny fraction of the partial CO<sub>2</sub> pressure in air, which is about 0.035 kPa.
  
−
==Shifts in function ==
+
At temperatures above 550&nbsp;°C the equilibrium CO<sub>2</sub> pressure begins to exceed the CO<sub>2</sub> pressure in air. So above 550&nbsp;°C, calcium carbonate begins to outgas CO<sub>2</sub> into air. However, in a charcoal fired kiln, the concentration of CO<sub>2</sub> will be much higher than it is in air. Indeed, if all the [[oxygen]] in the kiln is consumed in the fire, then the partial pressure of CO<sub>2</sub> in the kiln can be as high as 20 kPa.<ref name="solvaypcc2007">{{cite web|title = Solvay Precipitated Calcium Carbonate: Production|publisher = Solvay S. A. |date=9 March 2007|accessdate = 30 December 2007|url = http://www.solvaypcc.com/safety_environment/0,0,1000044-_EN,00.html}}</ref>
−
{{Quotation|''Adaptation and function are two aspects of one problem.''|Julian Huxley|Evolution: The Modern Synthesis<ref>{{harvnb|Huxley|1942|p=417}}</ref>}}
 
  
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===Pre-adaptation===
+
The table shows that this partial pressure is not achieved until the temperature is nearly 800&nbsp;°C. For the outgassing of CO<sub>2</sub> from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO<sub>2</sub>. And for it to happen rapidly, the equilibrium pressure must exceed total atmospheric pressure of 101 kPa, which happens at 898&nbsp;°C.{{clear right}}
  
−
Pre-adaptation occurs when a population has characteristics which by chance are suited for a set of conditions not previously experienced. For example, the polyploid [[Spartina|cordgrass]] ''Spartina townsendii'' is better adapted than either of its parent species to their own habitat of saline marsh and mud-flats.<ref>{{cite journal |last=Huskins |first=C. Leonard |authorlink=Charles Leonard Huskins |year=1930 |title=The origin of Spartina Townsendii |journal=[[Genetica]] |publisher=Martinus Nijhoff, The Hague/Kluwer Academic Publishers |volume=12 |issue=6 |pages=531–538 |doi=10.1007/BF01487665}}</ref> Among domestic animals, the [[Leghorn chicken|White Leghorn]] [[chicken]] is markedly more resistant to [[Thiamine|vitamin B<sub>1</sub>]] deficiency than other breeds; on a plentiful diet this makes no difference, but on a restricted diet this preadaptation could be decisive.<ref>{{cite journal |last1=Lamoreux |first1=Wilfred F. |last2=Hutt |first2=Frederick B. |date=February 15, 1939 |title=Breed differences in resistance to a deficiency in vitamin B<sub>1</sub> in the fowl |url=http://naldc.nal.usda.gov/download/IND43969284/PDF |journal=Journal of Agricultural Research |publisher=[[United States Department of Agriculture]] |volume=58 |issue=4 |pages=307–316}}</ref>
+
{| class="wikitable"
 +
|+ {{chembox header}} |Equilibrium pressure of CO<sub>2</sub> over CaCO<sub>3</sub> (P) vs. temperature (T).<ref name=crc>{{RubberBible86th}}</ref>
 +
|-
 +
|'''P (kPa)'''||0.055||0.13||0.31||1.80||5.9||9.3||14||24||34||51||72 ||80||91||101||179||901||3961
 +
|-
 +
|'''T (°C)'''||550||587||605||680||727||748||777||800||830||852||871||881||891||898||937||1082||1241
 +
|}
  
−
Pre-adaptation may arise because a natural population carries a huge quantity of genetic variability.<ref name="Dobzhansky T 1981">{{harvnb|Dobzhansky|1981}}</ref> In [[Ploidy#Diploid|diploid]] [[eukaryote]]s, this is a consequence of the system of [[sexual reproduction]], where mutant alleles get partially shielded, for example, by [[dominance (genetics)|genetic dominance]].<ref>{{cite book |first=R. C. |last=King |date=2006 |title=A Dictionary of Genetics |edition=7th|page=129 |publisher=Oxford University Press |isbn=978-0-19-530761-0 |url=https://books.google.com/books?id=ykp-7oJ5pREC&pg=PA129#v=onepage&f=false|quote=Dominance [refers] to alleles that fully manifest their phenotype when present in the [[zygosity|heterozygous]] ... state. |display-authors=etal}}</ref> [[Microorganism]]s, with their huge populations, also carry a great deal of genetic variability. The first experimental evidence of the pre-adaptive nature of genetic variants in microorganisms was provided by [[Salvador Luria]] and [[Max Delbrück]] who developed the [[Luria–Delbrück experiment|Fluctuation Test]], a method to show the random fluctuation of pre-existing genetic changes that conferred resistance to [[bacteriophage]]s in ''[[Escherichia coli]]''.<ref name="Luria 1943 491–511">{{cite journal |last=Luria |first=S. E. |author2=Delbrück, M. |year=1943 |title=Mutations of Bacteria from Virus Sensitivity to Virus Resistance |journal=[[Genetics (journal)|Genetics]] |volume=28 |issue=6 |pages=491–511 |url=http://www.genetics.org/cgi/reprint/28/6/491}}</ref>
+
==Solubility==
  
−
===Co-option of existing traits: exaptation ===
+
===With varying CO<sub>2</sub> pressure===
−
[[File:Sinosauropteryxfossil.jpg|thumb|upright=1.2|The feathers of ''[[Sinosauropteryx]]'', a dinosaur with feathers, were used for insulation, making them an [[exaptation]] for flight.]]
+
[[File:CanarySpring.jpg|thumb|right|[[Travertine]] calcium carbonate deposits from a [[hot spring]]]]
−
{{main|Exaptation}}
+
Calcium carbonate is poorly soluble in pure water (47&nbsp;mg/L at normal atmospheric CO<sub>2</sub> partial pressure as shown below).
  
−
Features that now appear as adaptations sometimes arose by co-option of existing traits, evolved for some other purpose. The classic example is the [[Evolution of mammalian auditory ossicles|ear ossicles of mammals]], which we know from [[Paleontology|paleontological]] and [[Embryology|embryological]] evidence originated in the upper and lower [[jaw]]s and the [[hyoid bone]] of their [[synapsid]] ancestors, and further back still were part of the [[Branchial arch|gill arch]]es of early fish.<ref>{{harvnb|Allin|Hopson|1992|pp=587–614}}</ref><ref>{{harvnb|Panchen|1992|loc=chpt. 4, "Homology and the evidence for evolution"}}</ref> The word ''exaptation'' was coined to cover these common evolutionary shifts in function.<ref>{{cite journal |last1=Gould |first1=Stephen Jay |author1link=Stephen Jay Gould |last2=Vrba |first2=Elizabeth S. |authorlink2=Elisabeth Vrba |date=Winter 1982 |title=Exaptation–A Missing Term in the Science of Form |journal=[[Paleobiology (journal)|Paleobiology]] |volume=8 |issue=1 |pages=4–15 |jstor=2400563}}</ref> The flight [[feather]]s of birds evolved from the much earlier [[Feathered dinosaur#List of non-avian dinosaur species preserved with evidence of feathers|feathers of dinosaur]]s,<ref name="Ornithoscelida">{{cite journal | last1=Baron | first1=M.G. | last2=Norman | first2=D.B. | last3=Barrett | first3=P.M. | year=2017 | title=A new hypothesis of dinosaur relationships and early dinosaur evolution | journal=Nature | volume=543 | issue=| pages=501–506 | doi=10.1038/nature21700| bibcode=2017Natur.543..501B }}</ref> which might have been used for insulation or for display.<ref name="Dimond et al">{{Cite journal|author1=Dimond, C. C. |author2=Cabin, R. J. |author3=Brooks, J. S. |journal=BIOS |title=Feathers, Dinosaurs, and Behavioral Cues: Defining the Visual Display Hypothesis for the Adaptive Function of Feathers in Non-Avian Theropods |volume=82|year=2011 |pages=58–63 |doi=10.1893/011.082.0302 |issue=3}}</ref><ref>{{Cite journal |author1=Sumida, S. S. |author2=C. A. Brochu |journal=American Zoologist|title=Phylogenetic Context for the Origin of Feathers |volume=40 |issue=4 |year=2000 |pages=485–503 |doi=10.1093/icb/40.4.486}}</ref>
+
The equilibrium of its solution is given by the equation (with dissolved calcium carbonate on the right):
 +
:{| width="500"
 +
| style="width:50%; height:30px;"| CaCO<sub>3</sub> {{eqm}} Ca<sup>2+</sup> + CO<sub>3</sub><sup>2−</sup>
 +
| ''K''<sub>sp</sub> = 3.7×10<sup>−9</sup> to 8.7×10<sup>−9</sup> at 25&nbsp;°C
 +
|}
  
−
==Non-adaptive traits ==
+
where the [[solubility product]] for [Ca<sup>2+</sup>] [CO<sub>3</sub><sup>2−</sup>] is given as anywhere from ''K''<sub>sp</sub> = 3.7×10<sup>−9</sup> to ''K''<sub>sp</sub> = 8.7×10<sup>−9</sup> at 25&nbsp;°C, depending upon the data source.<ref name = crc/><ref>{{cite web|title = Selected Solubility Products and Formation Constants at 25 °C|publisher = [[California State University, Dominguez Hills]]|url = http://www.csudh.edu/oliver/chemdata/data-ksp.htm}}</ref> What the equation means is that the product of molar concentration of calcium ions ([[mole (unit)|moles]] of dissolved Ca<sup>2+</sup> per liter of solution) with the molar concentration of dissolved CO<sub>3</sub><sup>2−</sup> cannot exceed the value of ''K''<sub>sp</sub>. This seemingly simple solubility equation, however, must be taken along with the more complicated equilibrium of [[carbon dioxide]] with [[water]] (see [[carbonic acid]]). Some of the CO<sub>3</sub><sup>2−</sup> combines with H<sup>+</sup> in the solution according to:
−
{{main|Spandrel (biology)|Vestigiality}}
 
  
−
Some traits do not appear to be adaptive, that is, they have a neutral or deleterious effect on fitness in the current environment. Because genes have [[Pleiotropy|pleiotropic]] effects, not all traits may be functional: they may be what [[Stephen Jay Gould]] and [[Richard Lewontin]] called [[Spandrel (biology)|spandrels]], features brought about by neighbouring adaptations, like the triangular areas under neighbouring arches in architecture which began as functionless features.<ref name=Wagner2014>[[Günter P. Wagner|Wagner, Günter P.]], ''Homology, Genes, and Evolutionary Innovation''. Princeton University Press. 2014. Chapter 1: The Intellectual Challenge of Morphological Evolution: A Case for Variational Structuralism. Page 7</ref>
+
:{| width="500"
 +
| style="width:50%; height:25px;"| HCO<sub>3</sub><sup>−</sup> {{eqm}} H<sup>+</sup> + CO<sub>3</sub><sup>2−</sup> &nbsp;&nbsp;
 +
| ''K''<sub>a2</sub> = 5.61×10<sup>−11</sup> at 25&nbsp;°C
 +
|}
  
−
Another possibility is that a trait may have been adaptive at some point in an organism's evolutionary history, but a change in habitats caused what used to be an adaptation to become unnecessary or even [[maladaptation|maladapted]]. Such adaptations are termed [[Vestigiality|vestigial]]. Many organisms have vestigial organs, which are the remnants of fully functional structures in their ancestors. As a result of changes in lifestyle the organs became redundant, and are either not functional or reduced in functionality. Since any structure represents some kind of cost to the general economy of the body, an advantage may accrue from their elimination once they are not functional. Examples: [[Wisdom tooth|wisdom teeth]] in humans; the loss of pigment and functional [[eye]]s in cave fauna; the loss of structure in [[Intestinal parasite|endoparasites]].<ref>{{harvnb|Barrett|Gautrey|Herbert|Kohn|1987}}. Charles Darwin was the first to put forward such ideas.</ref>
+
HCO<sub>3</sub><sup>−</sup> is known as the [[bicarbonate]] ion. [[Calcium bicarbonate]] is many times more soluble in water than calcium carbonate—indeed it exists ''only'' in solution.
  
−
==Extinction and coextinction ==
+
Some of the HCO<sub>3</sub><sup>−</sup> combines with H<sup>+</sup> in solution according to:
−
{{Main|Extinction|Coextinction}}
 
  
−
If a population cannot move or change sufficiently to preserve its long-term viability, then obviously, it will become extinct, at least in that locale. The species may or may not survive in other locales. Species extinction occurs when the death rate over the entire species exceeds the birth rate for a long enough period for the species to disappear. It was an observation of Van Valen that groups of species tend to have a characteristic and fairly regular rate of extinction.<ref>{{cite journal |last=Van Valen |first=Leigh |authorlink=Leigh Van Valen |date=July 1973 |title=A New Evolutionary Law |url=https://dl.dropboxusercontent.com/u/18310184/evolutionary-theory/vol-01/Vol.1%2CNo.1%2C1-30%2CL.%20Van%20Valen%2C%20A%20new%20evolutionary%20law..pdf |journal=Evolutionary Theory |volume=1 |pages=1–30}}</ref>
+
:{| width="500"
 +
| style="width:50%; height:25px;"|H<sub>2</sub>CO<sub>3</sub> {{eqm}} H<sup>+</sup> + HCO<sub>3</sub><sup>−</sup> &nbsp;&nbsp;
 +
| ''K''<sub>a1</sub> = 2.5×10<sup>−4</sup> at 25&nbsp;°C
 +
|}
  
−
Just as there is co-adaptation, there is also coextinction, the loss of a species due to the extinction of another with which it is coadapted, as with the extinction of a [[parasitism|parasitic]] insect following the loss of its host, or when a flowering plant loses its pollinator, or when a [[food chain]] is disrupted.<ref name="Koh">{{cite journal |last1=Koh |first1=Lian Pin |last2=Dunn |first2=Robert R. |authorlink2=Robert Dunn (biologist) |last3=Sodhi |first3=Navjot S. |last4=Colwell |first4=Robert K. |last5=Proctor |first5=Heather C. |last6=Smith |first6=Vincent S. |display-authors=3 |title=Species Coextinctions and the Biodiversity Crisis |date=September 2004 |journal=Science |volume=305 |issue=5690 |pages=1632–1634  |doi=10.1126/science.1101101 |pmid=15361627|bibcode=2004Sci...305.1632K }}</ref><ref>{{harvnb|Darwin|1872|pp=[http://darwin-online.org.uk/content/frameset?pageseq=84&itemID=F391&viewtype=side 57–58]}}. Darwin in tells the story of "a web of complex relations" involving heartsease (''[[Viola tricolor]]''), red clover (''[[Trifolium pratense]]''), [[bumblebee]]s, mice and cats.</ref>
+
Some of the H<sub>2</sub>CO<sub>3</sub> breaks up into water and dissolved carbon dioxide according to:
  
−
==Philosophical issues==
+
:{| width="500"
−
{{main|Adaptationism|Teleology in biology}}
+
| style="width:50%; height:25px;"| H<sub>2</sub>O + CO<sub>2</sub>(dissolved) {{eqm}} H<sub>2</sub>CO<sub>3</sub> &nbsp;&nbsp;
 +
| ''K''<sub>h</sub> = 1.70×10<sup>−3</sup> at 25&nbsp;°C
 +
|}
  
−
Adaptation raises [[Philosophy of biology|philosophical issues]] concerning how biologists speak of function and purpose, as this carries implications of evolutionary history – that a feature evolved by natural selection for a specific reason – and potentially of supernatural intervention – that features and organisms exist because of a deity's conscious intentions.<ref name="Sober1">{{harvnb|Sober|1993|pp=85–86}}</ref><ref>{{harvnb|Williams|1966|pp=8–10}}</ref> [[Aristotle's biology|In his biology, Aristotle]] introduced [[teleology]] to describe the adaptedness of organisms, but without accepting the supernatural intention built into [[Plato]]'s thinking, which Aristotle rejected.<ref>{{cite journal |last=Nagel |first=Ernest |authorlink=Ernest Nagel |date=May 1977 |title=Goal-Directed Processes in Biology |journal=[[The Journal of Philosophy]] |volume=74 |issue=5 |pages=261–279 |doi=10.2307/2025745 |jstor=2025745}} Teleology Revisisted: The Dewy Lectures 1977 (first lecture)</ref><ref>{{cite journal |last=Nagel |first=Ernest |date=May 1977 |title=Functional Explanations in Biology |journal=The Journal of Philosophy |volume=74 |issue=5 |pages=280–301 |doi=10.2307/2025746 |jstor=2025746}} Teleology Revisisted: The Dewy Lectures 1977 (second lecture)</ref> Modern biologists continue to face the same difficulty.<ref>{{harvnb|Pittendrigh|1958}}</ref><ref>{{harvnb|Mayr|1965|pp=33–50}}</ref><ref>{{harvnb|Mayr|1988|loc=chpt. 3, "The Multiple Meanings of Teleological"}}</ref><ref>{{harvnb|Williams|1966|loc="The Scientific Study of Adaptation"}}</ref><ref>{{harvnb|Monod|1971}}</ref><ref>{{cite encyclopedia |editor-last=Allaby |editor-first=Michael |editor-link=Michael Allaby |encyclopedia=A Dictionary of Zoology |title=teleonomy |url=https://books.google.com/books?id=1_UO957htTwC&pg=PA530&lpg=PA530 |accessdate=2015-08-24 |edition=Reissued with new cover and corrections |year=2003 |publisher=Oxford University Press |series=Oxford Paperback Reference |isbn=0-19-860758-X |oclc=444678726}}</ref> On the one hand, adaptation is obviously purposeful: natural selection chooses what works and eliminates what does not. On the other hand, biologists want to deny conscious purpose in evolution. The dilemma gave rise to a famous joke by the evolutionary biologist [[J. B. S. Haldane|Haldane]]: "Teleology is like a mistress to a biologist: he cannot live without her but he's unwilling to be seen with her in public.'" [[David Hull]] commented that Haldane's mistress "has become a lawfully wedded wife. Biologists no longer feel obligated to apologize for their use of teleological language; they flaunt it."<ref>{{harvnb|Hull|1982}}</ref>
+
And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to:
 +
 
 +
:{| width="500"
 +
| style="width:45%;"|<math chem>\frac{P_{\ce{CO2}}}{[\ce{CO2}]}\ =\ k_\ce{H}</math>
 +
| where ''k''<sub>H</sub> = 29.76 atm/(mol/L) at 25&nbsp;°C ([[Henry's law|Henry constant]]), <math chem>P_{\ce{CO2}}</math> being the CO<sub>2</sub> partial pressure.
 +
|}
 +
 
 +
For ambient air, <math chem>P_{\ce{CO2}}</math> is around 3.5×10<sup>−4</sup> atmospheres (or equivalently 35 [[Pascal (unit)|Pa]]). The last equation above fixes the concentration of dissolved CO<sub>2</sub> as a function of <math chem>P_{\ce{CO2}}</math>, independent of the concentration of dissolved CaCO<sub>3</sub>. At atmospheric partial pressure of CO<sub>2</sub>, dissolved CO<sub>2</sub> concentration is 1.2×10<sup>−5</sup> moles/liter. The equation before that fixes the concentration of H<sub>2</sub>CO<sub>3</sub> as a function of [CO<sub>2</sub>]. For [CO<sub>2</sub>]=1.2×10<sup>−5</sup>, it results in [H<sub>2</sub>CO<sub>3</sub>]=2.0×10<sup>−8</sup> moles per liter. When [H<sub>2</sub>CO<sub>3</sub>] is known, the remaining three equations together with
 +
{| class="wikitable floatright"
 +
|+ {{chembox header}} |Calcium ion solubility as a function of [[carbon dioxide|CO<sub>2</sub>]] [[partial pressure]] at 25&nbsp;°C {{math|1=(''K''<sub>sp</sub> = 4.47×10<sup>−9</sup>)}}
 +
|-
 +
!<math chem>\scriptstyle P_\ce{CO2}</math> (atm)
 +
![[pH]]
 +
![Ca<sup>2+</sup>] (mol/L)
 +
|-
 +
| 10<sup>−12</sup> ||12.0||5.19 × 10<sup>−3</sup>
 +
|-
 +
| 10<sup>−10</sup> ||11.3||1.12 × 10<sup>−3</sup>
 +
|-
 +
| 10<sup>−8</sup> ||10.7||2.55 × 10<sup>−4</sup>
 +
|-
 +
| 10<sup>−6</sup> ||9.83||1.20 × 10<sup>−4</sup>
 +
|-
 +
| 10<sup>−4</sup> ||8.62||3.16 × 10<sup>−4</sup>
 +
|-
 +
| 3.5 × 10<sup>−4</sup>||8.27||4.70 × 10<sup>−4</sup>
 +
|-
 +
| 10<sup>−3</sup> ||7.96||6.62 × 10<sup>−4</sup>
 +
|-
 +
| 10<sup>−2</sup> ||7.30||1.42 × 10<sup>−3</sup>
 +
|-
 +
| 10<sup>−1</sup> ||6.63||3.05 × 10<sup>−3</sup>
 +
|-
 +
| 1 ||5.96||6.58 × 10<sup>−3</sup>
 +
|-
 +
| 10 ||5.30||1.42 × 10<sup>−2</sup>
 +
|}
 +
 
 +
:{| width="450"
 +
| style="width:50%; height:25px;"| H<sub>2</sub>O {{eqm}} H<sup>+</sup> + OH<sup>−</sup>
 +
| ''K'' = 10<sup>−14</sup> at 25&nbsp;°C
 +
|}
 +
 
 +
(which is true for all aqueous solutions), and the fact that the solution must be electrically neutral,
 +
 
 +
:2[Ca<sup>2+</sup>] + [H<sup>+</sup>] = [HCO<sub>3</sub><sup>−</sup>] + 2[CO<sub>3</sub><sup>2−</sup>] + [OH<sup>−</sup>]
 +
 
 +
make it possible to solve simultaneously for the remaining five unknown concentrations (note that the above form of the neutrality equation is valid only if calcium carbonate has been put in contact with pure water or with a neutral pH solution; in the case where the initial water solvent pH is not neutral, the equation is modified).
 +
 
 +
The table on the right shows the result for [Ca<sup>2+</sup>] and [H<sup>+</sup>] (in the form of pH) as a function of ambient partial pressure of CO<sub>2</sub> (''K''<sub>sp</sub> = 4.47×10<sup>−9</sup> has been taken for the calculation).
 +
* At atmospheric levels of ambient CO<sub>2</sub> the table indicates the solution will be slightly alkaline with a maximum CaCO<sub>3</sub> solubility of 47&nbsp;mg/L.
 +
* As ambient CO<sub>2</sub> partial pressure is reduced below atmospheric levels, the solution becomes more and more alkaline. At extremely low <math chem>P_{\ce{CO2}}</math>, dissolved CO<sub>2</sub>, bicarbonate ion, and carbonate ion largely evaporate from the solution, leaving a highly alkaline solution of [[calcium hydroxide]], which is more soluble than CaCO<sub>3</sub>. Note that for <math chem>P_{\ce{CO2}} = 10^{-12} \mathrm{atm}</math>, the [Ca<sup>2+</sup>] [OH<sup>−</sup>]<sup>2</sup> product is still below the solubility product of Ca(OH)<sub>2</sub> (8×10<sup>−6</sup>). For still lower CO<sub>2</sub> pressure, Ca(OH)<sub>2</sub> precipitation will occur before CaCO<sub>3</sub> precipitation.
 +
* As ambient CO<sub>2</sub> partial pressure increases to levels above atmospheric, pH drops, and much of the carbonate ion is converted to bicarbonate ion, which results in higher solubility of Ca<sup>2+</sup>.
 +
 
 +
The effect of the latter is especially evident in day-to-day life of people who have hard water. Water in aquifers underground can be exposed to levels of CO<sub>2</sub> much higher than atmospheric. As such water percolates through calcium carbonate rock, the CaCO<sub>3</sub> dissolves according to the second trend. When that same water then emerges from the tap, in time it comes into equilibrium with CO<sub>2</sub> levels in the air by outgassing its excess CO<sub>2</sub>. The calcium carbonate becomes less soluble as a result and the excess precipitates as lime scale. This same process is responsible for the formation of [[stalactites]] and [[stalagmite]]s in limestone caves.
 +
 
 +
Two hydrated phases of calcium carbonate, [[monohydrocalcite]], CaCO<sub>3</sub>·H<sub>2</sub>O and [[ikaite]], CaCO<sub>3</sub>·6H<sub>2</sub>O, may [[precipitate]] from water at ambient conditions and persist as metastable phases.
 +
 
 +
=== With varying pH, temperature and salinity: CaCO<sub>3</sub> scaling in swimming pools ===
 +
[[File:CaCO3-pH.gif|thumb|alt=Effects of salinity and pH on the maximum calcium ion level before scaling is anticipated at 25 C and 1 mM bicarbonate (e.g. in swimming pools)]]
 +
[[File:CaCO3-Temp.gif|thumb|alt=Effects of temperature and bicarbonate concentration on the maximum calcium ion level before scaling is anticipated at pH 7 and 5,000 ppm salinity (e.g. in swimming pools)]]
 +
In contrast to the open equilibrium scenario above, many swimming pools are managed by addition of [[sodium bicarbonate]] (NaHCO<sub>3</sub>) to about 2 mM as a buffer, then control of pH through use of HCl, NaHSO<sub>4</sub>, Na<sub>2</sub>CO<sub>3</sub>, NaOH or chlorine formulations that are acidic or basic. In this situation, dissolved inorganic carbon ([[total inorganic carbon]]) is far from equilibrium with atmospheric CO<sub>2</sub>. Progress towards equilibrium through outgassing of CO<sub>2</sub> is slowed by (i) the slow reaction [[Carbonic acid|H<sub>2</sub>CO<sub>3</sub>]] ⇌ CO<sub>2</sub>(aq) + H<sub>2</sub>O;<ref>{{Cite journal | doi = 10.1021/jp909019u| pmid = 20039712| title = Comprehensive Study of the Hydration and Dehydration Reactions of Carbon Dioxide in Aqueous Solution| journal = The Journal of Physical Chemistry A| volume = 114| issue = 4| pages = 1734–40| year = 2010| last1 = Wang | first1 = X. | last2 = Conway | first2 = W. | last3 = Burns | first3 = R. | last4 = McCann | first4 = N. | last5 = Maeder | first5 = M. | bibcode = 2010JPCA..114.1734W}}</ref> (ii) limited aeration in a deep water column and (iii) periodic replenishment of bicarbonate to maintain buffer capacity (often estimated through measurement of [[alkalinity|‘total alkalinity’]]).
 +
 
 +
In this situation, the dissociation constants for the much faster reactions H<sub>2</sub>CO<sub>3</sub> ⇌ H<sup>+</sup> + HCO<sub>3</sub><sup>‾</sup> ⇌ 2 H<sup>+</sup> + CO<sub>3</sub><sup>2−</sup> allow the prediction of concentrations of each dissolved inorganic carbon species in solution, from the added concentration of HCO<sub>3</sub><sup>−</sup> (which constitutes more than 90% of [[Bjerrum plot]] species from pH 7 to pH 8 at 25&nbsp;°C in fresh water).<ref name="Mook 2000">Mook, W. (2000) [http://www-naweb.iaea.org/napc/ih/documents/global_cycle/vol%20I/cht_i_09.pdf "Chemistry of carbonic acid in water"], pp. 143–165 in ''Environmental Isotopes in the Hydrological Cycle: Principles and Applications''. INEA/UNESCO: Paris.</ref> Addition of HCO<sub>3</sub><sup>−</sup> will increase CO<sub>3</sub><sup>2−</sup> concentration at any pH. Rearranging the equations given above, we can see that [Ca<sup>2+</sup>] = Ksp / [CO<sub>3</sub><sup>2−</sup>], and [CO<sub>3</sub><sup>2−</sup>] = K<sub>a2</sub> × [HCO<sub>3</sub><sup>−</sup>] / [H<sup>+</sup>]. Therefore, when HCO<sub>3</sub><sup>−</sup> concentration is known, the maximum concentration of Ca<sup>2+</sup> ions before scaling through CaCO<sub>3</sub> precipitation can be predicted from the formula:
 +
 
 +
:Ca<sup>2+</sup><sub>max</sub> = (K<sub>sp</sub> / K<sub>a2</sub>) × ([H<sup>+</sup>] / [HCO<sub>3</sub><sup>−</sup>])
 +
 
 +
The solubility product for CaCO<sub>3</sub> (K<sub>sp</sub>) and the dissociation constants for the dissolved inorganic carbon species (including K<sub>a2</sub>) are all substantially affected by temperature and [[salinity]],<ref name="Mook 2000" /> with the overall effect that Ca<sup>2+</sup><sub>max</sub> increases from fresh to salt water, and decreases with rising temperature, pH, or added bicarbonate level, as illustrated in the accompanying graphs.
 +
 
 +
The trends are illustrative for pool management, but whether scaling occurs also depends on other factors including interactions with Mg<sup>2+</sup>, B(OH)<sub>4</sub><sup>−</sup> and other ions in the pool, as well as supersaturation effects.<ref>{{cite journal|author=Wojtowicz, J. A. |year=1998|title= Factors affecting precipitation of calcium carbonate|journal= Journal of the Swimming Pool and Spa Industry |volume=3 |issue=1|pages= 18–23|url=http://jspsi.poolhelp.com/ARTICLES/JSPSI_V3N1_pp18-23.pdf}}</ref><ref>{{cite journal|author=Wojtowicz, J. A. |year=1998|title= Corrections, potential errors, and significance of the saturation index|journal= Journal of the Swimming Pool and Spa Industry |volume=3 |issue=1|pages=37–40|url=http://jspsi.poolhelp.com/ARTICLES/JSPSI_V3N1_pp37-40.pdf}}</ref> Scaling is commonly observed in electrolytic chlorine generators, where there is a high pH near the cathode surface and scale deposition further increases temperature. This is one reason that some pool operators prefer borate over bicarbonate as the primary pH buffer, and avoid the use of pool chemicals containing calcium.<ref>Birch, R. G. (2013) [http://members.iinet.net.au/~jorobbirch/BABES.pdf BABES: a better method than "BBB" for pools with a salt-water chlorine generator.] iinet.net.au</ref>
 +
 
 +
===Solubility in a strong or weak acid solution===
 +
Solutions of [[strong acid|strong]] ([[hydrochloric acid|HCl]]), moderately strong ([[sulfamic acid|sulfamic]]) or [[weak acid|weak]] ([[acetic acid|acetic]], [[citric acid|citric]], [[sorbic acid|sorbic]], [[lactic acid|lactic]], [[phosphoric acid|phosphoric]]) acids are commercially available. They are commonly used as [[descaling agent]]s to remove [[limescale]] deposits. The maximum amount of CaCO<sub>3</sub> that can be "dissolved" by one liter of an acid solution can be calculated using the above equilibrium equations.
 +
* In the case of a strong monoacid with decreasing acid concentration [A] = [A<sup>−</sup>], we obtain (with CaCO<sub>3</sub> molar mass = 100 g):
 +
 
 +
{| border="1" cellspacing="0" cellpadding="4" style="margin: 0 0 0 0.5em; background: white; border-collapse: collapse; border-color: #C0C090;" class="wikitable"
 +
|-
 +
! width="160" {{chembox header}} |[A] (mol/L)
 +
| 1
 +
| 10<sup>−1</sup>
 +
| 10<sup>−2</sup>
 +
| 10<sup>−3</sup>
 +
| 10<sup>−4</sup>
 +
| 10<sup>−5</sup>
 +
| 10<sup>−6</sup>
 +
| 10<sup>−7</sup>
 +
| 10<sup>−10</sup>
 +
|-
 +
! width="160" {{chembox header}} |Initial pH
 +
| 0.00||1.00||2.00||3.00||4.00||5.00||6.00||6.79||7.00
 +
|-
 +
! width="160" {{chembox header}} |Final pH
 +
| 6.75||7.25||7.75||8.14||8.25||8.26||8.26||8.26||8.27
 +
|-
 +
! width="160" {{chembox header}} |Dissolved CaCO<sub>3</sub><br />(g/[[liter|L]] of acid)
 +
| 50.0||5.00||0.514||0.0849||0.0504||0.0474||0.0471||0.0470||0.0470
 +
|}
 +
 
 +
where the initial state is the acid solution with no Ca<sup>2+</sup> (not taking into account possible CO<sub>2</sub> dissolution) and the final state is the solution with saturated Ca<sup>2+</sup>. For strong acid concentrations, all species have a negligible concentration in the final state with respect to Ca<sup>2+</sup> and A<sup>−</sup> so that the neutrality equation reduces approximately to 2[Ca<sup>2+</sup>] = [A<sup>−</sup>] yielding <math>\scriptstyle[\mathrm{Ca}^{2+}] \simeq \frac{[\mathrm{A}^-]}{2}</math>. When the concentration decreases, [HCO<sub>3</sub><sup>−</sup>] becomes non-negligible so that the preceding expression is no longer valid. For vanishing acid concentrations, one can recover the final pH and the solubility of CaCO<sub>3</sub> in pure water.
 +
* In the case of a weak monoacid (here we take acetic acid with p''K''<sub>A</sub> = 4.76) with decreasing total acid concentration [A] = [A<sup>−</sup>]+[AH], we obtain:
 +
 
 +
{| border="1" cellspacing="0" cellpadding="4" style="margin: 0 0 0 0.5em; background: white; border-collapse: collapse; border-color: #C0C090;" class="wikitable"
 +
|-
 +
! width="160" {{chembox header}} |[A] (mol/L)
 +
| 1
 +
| 10<sup>−1</sup>
 +
| 10<sup>−2</sup>
 +
| 10<sup>−3</sup>
 +
| 10<sup>−4</sup>
 +
| 10<sup>−5</sup>
 +
| 10<sup>−6</sup>
 +
| 10<sup>−7</sup>
 +
| 10<sup>−10</sup>
 +
|-
 +
! width="160" {{chembox header}} |Initial pH
 +
| 2.38||2.88||3.39||3.91||4.47||5.15||6.02||6.79||7.00
 +
|-
 +
! width="160" {{chembox header}} |Final pH
 +
| 6.75||7.25||7.75||8.14||8.25||8.26||8.26||8.26||8.27
 +
|-
 +
! width="160" {{chembox header}} |Dissolved CaCO<sub>3</sub><br />(g/[[liter|L]] of acid)
 +
| 49.5||4.99||0.513||0.0848||0.0504||0.0474||0.0471||0.0470||0.0470
 +
|}
 +
For the same total acid concentration, the initial pH of the weak acid is less acid than the one of the strong acid; however, the maximum amount of CaCO<sub>3</sub> which can be dissolved is approximately the same. This is because in the final state, the pH is larger than the p''K''<sub>A</sub>, so that the weak acid is almost completely dissociated, yielding in the end as many H<sup>+</sup> ions as the strong acid to "dissolve" the calcium carbonate.
 +
* The calculation in the case of [[phosphoric acid]] (which is the most widely used for domestic applications) is more complicated since the concentrations of the four dissociation states corresponding to this acid must be calculated together with [HCO<sub>3</sub><sup>−</sup>], [CO<sub>3</sub><sup>2−</sup>], [Ca<sup>2+</sup>], [H<sup>+</sup>] and [OH<sup>−</sup>]. The system may be reduced to a seventh degree equation for [H<sup>+</sup>] the numerical solution of which gives
 +
 
 +
{| border="1" cellspacing="0" cellpadding="4" style="margin: 0 0 0 0.5em; background: white; border-collapse: collapse; border-color: #C0C090;" class="wikitable"
 +
|-
 +
! width="160" {{chembox header}} |[A] (mol/L)
 +
| 1
 +
| 10<sup>−1</sup>
 +
| 10<sup>−2</sup>
 +
| 10<sup>−3</sup>
 +
| 10<sup>−4</sup>
 +
| 10<sup>−5</sup>
 +
| 10<sup>−6</sup>
 +
| 10<sup>−7</sup>
 +
| 10<sup>−10</sup>
 +
|-
 +
! width="160" {{chembox header}} |Initial pH
 +
| 1.08||1.62||2.25||3.05||4.01||5.00||5.97||6.74||7.00
 +
|-
 +
! width="160" {{chembox header}} |Final pH
 +
| 6.71||7.17||7.63||8.06||8.24||8.26||8.26||8.26||8.27
 +
|-
 +
! width="160" {{chembox header}} |Dissolved CaCO<sub>3</sub><br />(g/[[liter|L]] of acid)
 +
| 62.0||7.39||0.874||0.123||0.0536||0.0477||0.0471||0.0471||0.0470
 +
|}
 +
 
 +
where [A] = [H<sub>3</sub>PO<sub>4</sub>] + [H<sub>2</sub>PO<sub>4</sub><sup>−</sup>] + [HPO<sub>4</sub><sup>2−</sup>] + [PO<sub>4</sub><sup>3−</sup>] is the total acid concentration. Thus phosphoric acid is more efficient than a monoacid since at the final almost neutral pH, the second dissociated state concentration [HPO<sub>4</sub><sup>2−</sup>] is not negligible (see [[phosphoric acid#pH and composition of a phosphoric acid aqueous solution|phosphoric acid]]).
  
 
==See also==
 
==See also==
−
{{Div col|colwidth=30em}}
+
{{div col|colwidth=22em}}
−
* [[Adaptive evolution in the human genome]]
+
* [[Cuttlebone]]
−
* [[Adaptive memory]]
+
* [[Cuttlefish]]
−
* [[Adaptive mutation]]
+
* [[Gesso]]
−
* [[Adaptive system]]
+
* [[Limescale]]
−
* [[Anti-predator adaptation]]
+
* [[Marble]]
−
* [[Body reactivity]]
+
* [[Ocean acidification]]
−
* [[Ecological trap]]
 
−
* [[Evolutionary pressure]]
 
−
* [[Evolvability]]
 
−
* [[Intragenomic conflict]]
 
−
* [[Neutral theory of molecular evolution]]
 
 
{{div col end}}
 
{{div col end}}
  
 
==References==
 
==References==
−
{{Reflist|30em}}
+
{{reflist|30em}}
 +
 
 +
==External links==
 +
* {{ICSC|1193|11}}
 +
* {{PubChemLink|516889}}
 +
* [[ATC codes]]: {{ATC|A02|AC01}} and {{ATC|A12|AA04}}
 +
* [http://calcium-carbonate.org.uk/calcium-carbonate.asp The British Calcium Carbonate Association – What is calcium carbonate]
 +
* [https://www.cdc.gov/niosh/npg/npgd0090.html CDC – NIOSH Pocket Guide to Chemical Hazards – Calcium Carbonate]
  
−
==Sources==
+
{{Calcium compounds}}
−
{{Refbegin|30em}}
+
{{Antacids}}
−
* {{cite book |last1=Allin |first1=Edgar F. |last2=Hopson |first2=James A. |authorlink2=James Hopson |year=1992 |chapter=Evolution of the Auditory System in Synapsida ("Mammal-Like Reptiles" and Primitive Mammals) as Seen in the Fossil Record |editor1-last=Webster |editor1-first=Douglas B. |editor2-last=Fay |editor2-first=Richard R. |editor3-last=Popper |editor3-first=Arthur N. |title=The Evolutionary Biology of Hearing |publisher=[[Springer Science+Business Media|Springer-Verlag]] |doi=10.1007/978-1-4612-2784-7_37 |isbn=0-387-97588-8 |oclc=23582549 |ref=harv}} "Based on a conference held at the [[Mote Marine Laboratory]] in Sarasota, Fla., May 20–24, 1990."
+
{{Drugs for treatment of hyperkalemia and hyperphosphatemia}}
−
* {{cite book |editor1-last=Barrett |editor1-first=Paul H. |editor2-last=Gautrey |editor2-first=Peter J. |editor3-last=Herbert |editor3-first=Sandra |editor4-last=Kohn |editor4-first=David |editor5-last=Smith |display-editors=3 |editor5-first=Sydney |year=1987 |title=Charles Darwin's Notebooks, 1836-1844: Geology, Transmutation of Species, Metaphysical Enquiries |publisher=[[Cornell University Press]] |isbn=0-521-09975-7 |oclc=16224403 |ref=harv}}
 
−
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* {{cite book |last=Eldredge |first=Niles |year=1995 |title=Reinventing Darwin: The Great Debate at the High Table of Evolutionary Theory |publisher=[[John Wiley & Sons]] |isbn=0-471-30301-1 |oclc=30975979 |ref=harv}}
 
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* {{cite book |last=Endler |first=John A. |authorlink=John Endler |year=1986 |chapter=Fitness and Adaptation |series=Monographs in Population Biology |volume=21 |title=Natural Selection in the Wild |publisher=[[Princeton University Press]] |isbn=0-691-08387-8 |oclc=12262762 |ref=harv}}
 
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* {{cite book |last=Fisher |first=Ronald Aylmer |authorlink=Ronald Fisher |year=1930 |title=[[The Genetical Theory of Natural Selection]] |publisher=[[Oxford University Press#The Clarendon Press|The Clarendon Press]] |oclc=493745635 |ref=harv}}
 
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* {{cite book |last=Ford |first=E. B. |year=1975 |title=[[Ecological Genetics (book)|Ecological Genetics]] |edition=4th |publisher=[[Chapman & Hall]]; John Wiley & Sons |isbn=0-470-26576-0 |oclc=1890603 |ref=harv}}
 
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* {{cite book |last1=Freeman |first1=Scott |last2=Herron |first2=Jon C. |year=2007 |title=Evolutionary Analysis |edition=4th |publisher=[[Prentice Hall|Pearson Prentice Hall]] |isbn=0-13-227584-8 |oclc=73502978 |ref=harv}}
 
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* {{cite book |last=Futuyma |first=Douglas J. |authorlink=Douglas J. Futuyma |year=1986 |title=Evolutionary Biology |edition=2nd |publisher=[[Sinauer Associates]] |isbn=0-87893-188-0 |oclc=13822044 |ref=harv}}
 
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* {{cite book |last=Hutchinson |first=G. Evelyn |authorlink=G. Evelyn Hutchinson |year=1965 |title=The Ecological Theater and the Evolutionary Play |publisher=[[Yale University Press]]|oclc=250039 |ref=harv}}
 
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* {{cite book |last=Huxley |first=Julian |authorlink=Julian Huxley |year=1942 |title=[[Evolution: The Modern Synthesis]] |publisher=[[Allen & Unwin]] |oclc=1399386 |ref=harv}}
 
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* {{cite book |editor1-last=Margulis |editor1-first=Lynn |editor1-link=Lynn Margulis |editor2-last=Fester |editor2-first=René |year=1991 |title=Symbiosis as a Source of Evolutionary Innovation: Speciation and Morphogenesis  |publisher=[[MIT Press]] |isbn=0-262-13269-9 |oclc=22597587 |ref=harv}} "Based on a conference held in Bellagio, Italy, June 25–30, 1989"
 
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* {{cite book |last=Maynard Smith |first=John |year=1993 |title=The Theory of Evolution |edition=Canto  |publisher=Cambridge University Press |isbn=0-521-45128-0 |oclc=27676642 |ref=harv}}
 
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* {{cite book |last=Wright |first=Sewall |authorlink=Sewall Wright |year=1932 |chapter=The Roles of Mutation, Inbreeding, Crossbreeding and Selection in Evolution |editor-last=Jones |editor-first=Donald F. |editor-link=Donald F. Jones |title=Proceedings of the Sixth International Congress of Genetics |volume=1 |publisher=[[Genetics Society of America]] |oclc=439596433 |ref=harv}}
 
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[[Category:Evolutionary biology]]
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{{DEFAULTSORT:Calcium Carbonate}}
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[[Category:Calcium compounds]]
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[[Category:Carbonates]]
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[[Category:Limestone]]
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[[Category:Phosphate binders]]
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[[Category:Excipients]]
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[[Category:Antacids]]
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[[Category:Food stabilizers]]

Revision as of 17:55, 27 July 2018

Template:Use dmy dates Template:Chembox

File:Calcite.png
Crystal structure of calcite

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock build mainly of calcite) and is the main component of pearls and the shells of marine organisms, snails, and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

Chemistry

Calcium carbonate shares the typical properties of other carbonates. Notably,

CaCO3(s) + 2H+(aq) → Ca2+(aq) + CO2(g) + H2O (l)
CaCO3 (s) → CaO (s) + CO2 (g)

Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.

CaCO3 + CO2 + H2O → Ca(HCO3)2

This reaction is important in the erosion of carbonate rock, forming caverns, and leads to hard water in many regions.

An unusual form of calcium carbonate is the hexahydrate, ikaite, CaCO3·6H2O. Ikaite is stable only below 6 °C.

Preparation

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually marble).

Alternatively, calcium carbonate is prepared from calcium oxide. Water is added to give calcium hydroxide then carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC):<ref name="PCC">Template:Cite web</ref>

CaO + H2O → Ca(OH)2
<chem>Ca(OH)2 + CO2 -> CaCO3(v) + H2O</chem>

Structure

The thermodynamically stable form of CaCO3 under normal conditions is hexagonal β-CaCO3, (the mineral calcite).<ref name ="Ropp">Template:Cite book</ref> Other forms can be prepared, the denser,(2.83 g/cc) orthorhombic λ-CaCO3 ( the mineral aragonite) and μ-CaCO3, occurring as the mineral vaterite.<ref name ="Ropp"/> The aragonite form can be prepared by precipitation at temperatures above 85 °C, the vaterite form can be prepared by precipitation at 60 °C.<ref name ="Ropp"/> Calcite contains calcium atoms coordinated by 6 oxygen atoms, in aragonite they are coordinated by 9 oxygen atoms.<ref name ="Ropp"/> The vaterite structure is not fully understood.<ref name="DemichelisRaiteri2013">Template:Cite journal</ref> Magnesium carbonate MgCO3 has the calcite structure, whereas strontium and barium carbonate (SrCO3 and BaCO3) adopt the aragonite structure, reflecting their larger ionic radii.<ref name ="Ropp"/>

Occurrence

File:Calcium carbonate chunks.JPG
Calcium carbonate chunks from clamshell

Geological sources

Calcite, aragonite and vaterite are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include limestone, chalk, marble and travertine.

File:Silfurberg.jpg
Calcite is the most stable polymorph of calcium carbonate. It is transparent to opaque. A transparent variety called Iceland spar (shown here) is used for optical purposes.Template:Clarify

Biological sources

Eggshells, snail shells and most seashells are predominantly calcium carbonate and can be used as industrial sources of that chemical.<ref>Template:Cite web</ref> Oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, however, they are not practical as an industrial source.<ref>Template:Cite journal</ref>

Extraterrestrial

Beyond Earth, strong evidence suggests the presence of calcium carbonate on Mars. Signs of calcium carbonate have been detected at more than one location (notably at Gusev and Huygens craters). This provides some evidence for the past presence of liquid water.<ref>Template:Cite journal</ref><ref name=Clark2007> Template:Cite journal</ref>

Geology

Carbonate is found frequently in geologic settings and constitutes an enormous carbon reservoir. Calcium carbonate occurs as aragonite, calcite and dolomite. The carbonate minerals form the rock types: limestone, chalk, marble, travertine, tufa, and others.

In warm, clear tropical waters corals are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including plankton (such as coccoliths and planktic foraminifera), coralline algae, sponges, brachiopods, echinoderms, bryozoa and mollusks, are typically found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate. The calcification processes are changed by ocean acidification.

Where the oceanic crust is subducted under a continental plate sediments will be carried down to warmer zones in the asthenosphere and lithosphere. Under these conditions calcium carbonate decomposes to produce carbon dioxide which, along with other gases, give rise to explosive volcanic eruptions.

Carbonate compensation depth

The carbonate compensation depth (CCD) is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature drops and pressure increases. Calcium carbonate is unusual in that its solubility increases with decreasing temperature. Increasing pressure also increases the solubility of calcium carbonate. The carbonate compensation depth can range from 4–6 km below sea level.

Role in taphonomy

Calcium carbonate can preserve fossils through permineralization. Most of the vertebrate fossils of the Two Medicine Formation—a geologic formation known for its duck-billed dinosaur eggs—are preserved by CaCO3 permineralization.<ref name="twoturn" /> This type of preservation conserves high levels of detail, even down to the microscopic level. However, it also leaves specimens vulnerable to weathering when exposed to the surface.<ref name="twoturn">Trexler, D. (2001) "Two Medicine Formation, Montana: geology and fauna", pp. 298–309 in Mesozoic Vertebrate Life, Tanke, D. H., and Carpenter, K. (eds), Indiana University Press. Template:ISBN</ref>

Trilobite populations were once thought to have composed the majority of aquatic life during the Cambrian, due to the fact that their calcium carbonate-rich shells were more easily preserved than those of other species,<ref>Template:Cite book</ref> which had purely chitinous shells.

Uses

Industrial applications

The main use of calcium carbonate is in the construction industry, either as a building material or limestone aggregate for road building or as an ingredient of cement or as the starting material for the preparation of builder's lime by burning in a kiln. However, because of weathering mainly caused by acid rain,<ref>Template:Cite web</ref> calcium carbonate (in limestone form) is no longer used for building purposes on its own, but only as a raw/primary substance for building materials.

Calcium carbonate is also used in the purification of iron from iron ore in a blast furnace. The carbonate is calcined in situ to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron.<ref>Template:Cite web</ref>

In the oil industry, calcium carbonate is added to drilling fluids as a formation-bridging and filtercake-sealing agent; it is also a weighting material which increases the density of drilling fluids to control the downhole pressure. Calcium carbonate is added to swimming pools, as a pH corrector for maintaining alkalinity and offsetting the acidic properties of the disinfectant agent.Template:Citation needed

It is also used as a raw material in the refining of sugar from sugar beet; It is calcined in a kiln with anthracite to produce calcium oxide and carbon dioxide. This burnt lime is then slaked in sweet water to produce a calcium hydroxide suspension for the precipitation of impurities in raw juice during carbonatation.<ref>Template:Cite book</ref>

Calcium carbonate has traditionally been a major component of blackboard chalk. However, modern manufactured chalk is mostly gypsum, hydrated calcium sulfate CaSO4·2H2O. Calcium carbonate is a main source for growing Seacrete, or Biorock. Precipitated calcium carbonate (PCC), pre-dispersed in slurry form, is a common filler material for latex gloves with the aim of achieving maximum saving in material and production costs.<ref name=precaco3>Template:Cite web</ref>

Fine ground calcium carbonate (GCC) is an essential ingredient in the microporous film used in diapers and some building films as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. GCC or PCC is used as a filler in paper because they are cheaper than wood fiber. In terms of market volume, GCC are the most important types of fillers currently used.<ref>Market Study Fillers, 2nd ed., published by Ceresana, September 2011</ref> Printing and writing paper can contain 10–20% calcium carbonate. In North America, calcium carbonate has begun to replace kaolin in the production of glossy paper. Europe has been practicing this as alkaline papermaking or acid-free papermaking for some decades. PCC used for paper filling and paper coatings is precipitated and prepared in a variety of shapes and sizes having characteristic narrow particle size distributions and equivalent spherical diameters of 0.4 to 3 micrometres.Template:Citation needed

Calcium carbonate is widely used as an extender in paints,<ref name = reade>Template:Cite web</ref> in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics.<ref name = reade/> Some typical examples include around 15 to 20% loading of chalk in unplasticized polyvinyl chloride (uPVC) drain pipe, 5 to 15% loading of stearate coated chalk or marble in uPVC window profile. PVC cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation) and electrical properties (volume resistivity).Template:Citation needed Polypropylene compounds are often filled with calcium carbonate to increase rigidity, a requirement that becomes important at high use temperatures.<ref name= Imerys>Template:Cite web</ref> Here the percentage is often 20–40%. It also routinely used as a filler in thermosetting resins (sheet and bulk molding compounds)<ref name = Imerys/> and has also been mixed with ABS, and other ingredients, to form some types of compression molded "clay" poker chips.Template:Citation needed Precipitated calcium carbonate, made by dropping calcium oxide into water, is used by itself or with additives as a white paint, known as whitewashing.Template:Citation needed

Calcium carbonate is added to a wide range of trade and do it yourself adhesives, sealants, and decorating fillers.<ref name = reade/> Ceramic tile adhesives typically contain 70 to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting stained glass windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature.Template:Citation needed

In ceramics/glazing applications, calcium carbonate is known as whiting,<ref name = reade/> and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. Ground calcium carbonate is an abrasive (both as scouring powder and as an ingredient of household scouring creams), in particular in its calcite form, which has the relatively low hardness level of 3 on the Mohs scale of mineral hardness, and will therefore not scratch glass and most other ceramics, enamel, bronze, iron, and steel, and have a moderate effect on softer metals like aluminium and copper. A paste made from calcium carbonate and deionized water can be used to clean tarnish on silver.<ref name="Make it Shine">Template:Cite web</ref>

Health and dietary applications

File:500 mg calcium supplements with vitamin D.jpg
500-milligram calcium supplements made from calcium carbonate

Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement for gastric antacid<ref name = medline>Template:Cite web</ref> (e.g., Tums). It may be used as a phosphate binder for the treatment of hyperphosphatemia (primarily in patients with chronic renal failure). It is also used in the pharmaceutical industry as an inert filler for tablets and other pharmaceuticals.<ref>Template:Cite book</ref>

Calcium carbonate is used in the production of calcium oxide as well as toothpaste and has seen a resurgence as a food preservative and color retainer, when used in or with products such as organic apples.<ref>Food Additives – Names Starting with C. Chemistry.about.com (10 April 2012). Retrieved 2012-05-24.</ref>

Excess calcium from supplements, fortified food and high-calcium diets, can cause milk-alkali syndrome, which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in renal failure, alkalosis, and hypercalcaemia, mostly in men with peptic ulcer disease. These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting. Milk-alkali syndrome declined in men after effective treatments for peptic ulcer disease arose. During the past 15 years, it has been reported in women taking calcium supplements above the recommended range of 1.2 to 1.5 g daily, for prevention and treatment of osteoporosis, and is exacerbated by dehydration. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. Excessive calcium intake can lead to hypercalcemia, complications of which include vomiting, abdominal pain and altered mental status.<ref>Template:Cite journal</ref>

As a food additive it is designated E170,<ref>Template:Cite web 080419 food-info.net</ref> and it has an INS number of 170. Used as an acidity regulator, anticaking agent, stabiliser or colour it is approved for usage in the EU,<ref>UK Food Standards Agency: Template:Cite web</ref> USA<ref>US Food and Drug Administration: Template:Cite web</ref> and Australia and New Zealand.<ref>Australia New Zealand Food Standards CodeTemplate:Cite web</ref> It is used in some soy milk and almond milk products as a source of dietary calcium; one study suggests that calcium carbonate might be as bioavailable as the calcium in cow's milk.<ref>Template:Cite journal</ref> Calcium carbonate is also used as a firming agent in many canned or bottled vegetable products.

Agricultural use

Agricultural lime, powdered chalk or limestone, is used as a cheap method for neutralising acidic soil, making it suitable for planting.<ref name="Oates2008">Template:Cite book</ref>

Household use

Calcium carbonate is a key ingredient in many household cleaning powders like Comet (cleanser) and is used as a scrubbing agent.

Environmental applications

In 1989, a researcher, Ken Simmons, introduced CaCO3 into the Whetstone Brook in Massachusetts.<ref>Template:Cite news</ref> His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Although his experiment was a success, it did increase the amount of aluminium ions in the area of the brook that was not treated with the limestone. This shows that CaCO3 can be added to neutralize the effects of acid rain in river ecosystems. Currently calcium carbonate is used to neutralize acidic conditions in both soil and water.<ref name=env>Template:Cite web</ref><ref>Template:Cite journal</ref><ref>Template:Cite web</ref> Since the 1970s, such liming has been practiced on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly.<ref>Template:Cite journal</ref>

Calcium carbonate is also used in flue gas desulfurisation applications eliminating harmful SO2 and NO2 emissions from coal and other fossil fuels burnt in large fossil fuel power stations.<ref name=env/>

Calcination equilibrium

Calcination of limestone using charcoal fires to produce quicklime has been practiced since antiquity by cultures all over the world. The temperature at which limestone yields calcium oxide is usually given as 825 °C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and carbon dioxide at any temperature. At each temperature there is a partial pressure of carbon dioxide that is in equilibrium with calcium carbonate. At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO2 pressure is only a tiny fraction of the partial CO2 pressure in air, which is about 0.035 kPa.

At temperatures above 550 °C the equilibrium CO2 pressure begins to exceed the CO2 pressure in air. So above 550 °C, calcium carbonate begins to outgas CO2 into air. However, in a charcoal fired kiln, the concentration of CO2 will be much higher than it is in air. Indeed, if all the oxygen in the kiln is consumed in the fire, then the partial pressure of CO2 in the kiln can be as high as 20 kPa.<ref name="solvaypcc2007">Template:Cite web</ref>

The table shows that this partial pressure is not achieved until the temperature is nearly 800 °C. For the outgassing of CO2 from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO2. And for it to happen rapidly, the equilibrium pressure must exceed total atmospheric pressure of 101 kPa, which happens at 898 °C.Template:Clear right

Template:Chembox header |Equilibrium pressure of CO2 over CaCO3 (P) vs. temperature (T).<ref name=crc>Template:RubberBible86th</ref>
P (kPa) 0.055 0.13 0.31 1.80 5.9 9.3 14 24 34 51 72 80 91 101 179 901 3961
T (°C) 550 587 605 680 727 748 777 800 830 852 871 881 891 898 937 1082 1241

Solubility

With varying CO2 pressure

File:CanarySpring.jpg
Travertine calcium carbonate deposits from a hot spring

Calcium carbonate is poorly soluble in pure water (47 mg/L at normal atmospheric CO2 partial pressure as shown below).

The equilibrium of its solution is given by the equation (with dissolved calcium carbonate on the right):

CaCO3 Template:Eqm Ca2+ + CO32− Ksp = 3.7×10−9 to 8.7×10−9 at 25 °C

where the solubility product for [Ca2+] [CO32−] is given as anywhere from Ksp = 3.7×10−9 to Ksp = 8.7×10−9 at 25 °C, depending upon the data source.<ref name = crc/><ref>Template:Cite web</ref> What the equation means is that the product of molar concentration of calcium ions (moles of dissolved Ca2+ per liter of solution) with the molar concentration of dissolved CO32− cannot exceed the value of Ksp. This seemingly simple solubility equation, however, must be taken along with the more complicated equilibrium of carbon dioxide with water (see carbonic acid). Some of the CO32− combines with H+ in the solution according to:

HCO3− Template:Eqm H+ + CO32−    Ka2 = 5.61×10−11 at 25 °C

HCO3− is known as the bicarbonate ion. Calcium bicarbonate is many times more soluble in water than calcium carbonate—indeed it exists only in solution.

Some of the HCO3− combines with H+ in solution according to:

H2CO3 Template:Eqm H+ + HCO3−    Ka1 = 2.5×10−4 at 25 °C

Some of the H2CO3 breaks up into water and dissolved carbon dioxide according to:

H2O + CO2(dissolved) Template:Eqm H2CO3    Kh = 1.70×10−3 at 25 °C

And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to:

<math chem>\frac{P_{\ce{CO2}}}{[\ce{CO2}]}\ =\ k_\ce{H}</math> where kH = 29.76 atm/(mol/L) at 25 °C (Henry constant), <math chem>P_{\ce{CO2}}</math> being the CO2 partial pressure.

For ambient air, <math chem>P_{\ce{CO2}}</math> is around 3.5×10−4 atmospheres (or equivalently 35 Pa). The last equation above fixes the concentration of dissolved CO2 as a function of <math chem>P_{\ce{CO2}}</math>, independent of the concentration of dissolved CaCO3. At atmospheric partial pressure of CO2, dissolved CO2 concentration is 1.2×10−5 moles/liter. The equation before that fixes the concentration of H2CO3 as a function of [CO2]. For [CO2]=1.2×10−5, it results in [H2CO3]=2.0×10−8 moles per liter. When [H2CO3] is known, the remaining three equations together with

Template:Chembox header |Calcium ion solubility as a function of CO2 partial pressure at 25 °C Template:Math
<math chem>\scriptstyle P_\ce{CO2}</math> (atm) pH [Ca2+] (mol/L)
10−12 12.0 5.19 × 10−3
10−10 11.3 1.12 × 10−3
10−8 10.7 2.55 × 10−4
10−6 9.83 1.20 × 10−4
10−4 8.62 3.16 × 10−4
3.5 × 10−4 8.27 4.70 × 10−4
10−3 7.96 6.62 × 10−4
10−2 7.30 1.42 × 10−3
10−1 6.63 3.05 × 10−3
1 5.96 6.58 × 10−3
10 5.30 1.42 × 10−2
H2O Template:Eqm H+ + OH− K = 10−14 at 25 °C

(which is true for all aqueous solutions), and the fact that the solution must be electrically neutral,

2[Ca2+] + [H+] = [HCO3−] + 2[CO32−] + [OH−]

make it possible to solve simultaneously for the remaining five unknown concentrations (note that the above form of the neutrality equation is valid only if calcium carbonate has been put in contact with pure water or with a neutral pH solution; in the case where the initial water solvent pH is not neutral, the equation is modified).

The table on the right shows the result for [Ca2+] and [H+] (in the form of pH) as a function of ambient partial pressure of CO2 (Ksp = 4.47×10−9 has been taken for the calculation).

  • At atmospheric levels of ambient CO2 the table indicates the solution will be slightly alkaline with a maximum CaCO3 solubility of 47 mg/L.
  • As ambient CO2 partial pressure is reduced below atmospheric levels, the solution becomes more and more alkaline. At extremely low <math chem>P_{\ce{CO2}}</math>, dissolved CO2, bicarbonate ion, and carbonate ion largely evaporate from the solution, leaving a highly alkaline solution of calcium hydroxide, which is more soluble than CaCO3. Note that for <math chem>P_{\ce{CO2}} = 10^{-12} \mathrm{atm}</math>, the [Ca2+] [OH−]2 product is still below the solubility product of Ca(OH)2 (8×10−6). For still lower CO2 pressure, Ca(OH)2 precipitation will occur before CaCO3 precipitation.
  • As ambient CO2 partial pressure increases to levels above atmospheric, pH drops, and much of the carbonate ion is converted to bicarbonate ion, which results in higher solubility of Ca2+.

The effect of the latter is especially evident in day-to-day life of people who have hard water. Water in aquifers underground can be exposed to levels of CO2 much higher than atmospheric. As such water percolates through calcium carbonate rock, the CaCO3 dissolves according to the second trend. When that same water then emerges from the tap, in time it comes into equilibrium with CO2 levels in the air by outgassing its excess CO2. The calcium carbonate becomes less soluble as a result and the excess precipitates as lime scale. This same process is responsible for the formation of stalactites and stalagmites in limestone caves.

Two hydrated phases of calcium carbonate, monohydrocalcite, CaCO3·H2O and ikaite, CaCO3·6H2O, may precipitate from water at ambient conditions and persist as metastable phases.

With varying pH, temperature and salinity: CaCO3 scaling in swimming pools

File:CaCO3-pH.gif
File:CaCO3-Temp.gif

In contrast to the open equilibrium scenario above, many swimming pools are managed by addition of sodium bicarbonate (NaHCO3) to about 2 mM as a buffer, then control of pH through use of HCl, NaHSO4, Na2CO3, NaOH or chlorine formulations that are acidic or basic. In this situation, dissolved inorganic carbon (total inorganic carbon) is far from equilibrium with atmospheric CO2. Progress towards equilibrium through outgassing of CO2 is slowed by (i) the slow reaction H2CO3 ⇌ CO2(aq) + H2O;<ref>Template:Cite journal</ref> (ii) limited aeration in a deep water column and (iii) periodic replenishment of bicarbonate to maintain buffer capacity (often estimated through measurement of ‘total alkalinity’).

In this situation, the dissociation constants for the much faster reactions H2CO3 ⇌ H+ + HCO3‾ ⇌ 2 H+ + CO32− allow the prediction of concentrations of each dissolved inorganic carbon species in solution, from the added concentration of HCO3− (which constitutes more than 90% of Bjerrum plot species from pH 7 to pH 8 at 25 °C in fresh water).<ref name="Mook 2000">Mook, W. (2000) "Chemistry of carbonic acid in water", pp. 143–165 in Environmental Isotopes in the Hydrological Cycle: Principles and Applications. INEA/UNESCO: Paris.</ref> Addition of HCO3− will increase CO32− concentration at any pH. Rearranging the equations given above, we can see that [Ca2+] = Ksp / [CO32−], and [CO32−] = Ka2 × [HCO3−] / [H+]. Therefore, when HCO3− concentration is known, the maximum concentration of Ca2+ ions before scaling through CaCO3 precipitation can be predicted from the formula:

Ca2+max = (Ksp / Ka2) × ([H+] / [HCO3−])

The solubility product for CaCO3 (Ksp) and the dissociation constants for the dissolved inorganic carbon species (including Ka2) are all substantially affected by temperature and salinity,<ref name="Mook 2000" /> with the overall effect that Ca2+max increases from fresh to salt water, and decreases with rising temperature, pH, or added bicarbonate level, as illustrated in the accompanying graphs.

The trends are illustrative for pool management, but whether scaling occurs also depends on other factors including interactions with Mg2+, B(OH)4− and other ions in the pool, as well as supersaturation effects.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Scaling is commonly observed in electrolytic chlorine generators, where there is a high pH near the cathode surface and scale deposition further increases temperature. This is one reason that some pool operators prefer borate over bicarbonate as the primary pH buffer, and avoid the use of pool chemicals containing calcium.<ref>Birch, R. G. (2013) BABES: a better method than "BBB" for pools with a salt-water chlorine generator. iinet.net.au</ref>

Solubility in a strong or weak acid solution

Solutions of strong (HCl), moderately strong (sulfamic) or weak (acetic, citric, sorbic, lactic, phosphoric) acids are commercially available. They are commonly used as descaling agents to remove limescale deposits. The maximum amount of CaCO3 that can be "dissolved" by one liter of an acid solution can be calculated using the above equilibrium equations.

  • In the case of a strong monoacid with decreasing acid concentration [A] = [A−], we obtain (with CaCO3 molar mass = 100 g):
width="160" Template:Chembox header |[A] (mol/L) 1 10−1 10−2 10−3 10−4 10−5 10−6 10−7 10−10
width="160" Template:Chembox header |Initial pH 0.00 1.00 2.00 3.00 4.00 5.00 6.00 6.79 7.00
width="160" Template:Chembox header |Final pH 6.75 7.25 7.75 8.14 8.25 8.26 8.26 8.26 8.27
width="160" Template:Chembox header |Dissolved CaCO3
(g/L of acid) 		50.0 5.00 0.514 0.0849 0.0504 0.0474 0.0471 0.0470 0.0470

where the initial state is the acid solution with no Ca2+ (not taking into account possible CO2 dissolution) and the final state is the solution with saturated Ca2+. For strong acid concentrations, all species have a negligible concentration in the final state with respect to Ca2+ and A− so that the neutrality equation reduces approximately to 2[Ca2+] = [A−] yielding \(\scriptstyle[\mathrm{Ca}^{2+}] \simeq \frac{[\mathrm{A}^-]}{2}\). When the concentration decreases, [HCO3−] becomes non-negligible so that the preceding expression is no longer valid. For vanishing acid concentrations, one can recover the final pH and the solubility of CaCO3 in pure water.

  • In the case of a weak monoacid (here we take acetic acid with pKA = 4.76) with decreasing total acid concentration [A] = [A−]+[AH], we obtain:
width="160" Template:Chembox header |[A] (mol/L) 1 10−1 10−2 10−3 10−4 10−5 10−6 10−7 10−10
width="160" Template:Chembox header |Initial pH 2.38 2.88 3.39 3.91 4.47 5.15 6.02 6.79 7.00
width="160" Template:Chembox header |Final pH 6.75 7.25 7.75 8.14 8.25 8.26 8.26 8.26 8.27
width="160" Template:Chembox header |Dissolved CaCO3
(g/L of acid) 		49.5 4.99 0.513 0.0848 0.0504 0.0474 0.0471 0.0470 0.0470

For the same total acid concentration, the initial pH of the weak acid is less acid than the one of the strong acid; however, the maximum amount of CaCO3 which can be dissolved is approximately the same. This is because in the final state, the pH is larger than the pKA, so that the weak acid is almost completely dissociated, yielding in the end as many H+ ions as the strong acid to "dissolve" the calcium carbonate.

  • The calculation in the case of phosphoric acid (which is the most widely used for domestic applications) is more complicated since the concentrations of the four dissociation states corresponding to this acid must be calculated together with [HCO3−], [CO32−], [Ca2+], [H+] and [OH−]. The system may be reduced to a seventh degree equation for [H+] the numerical solution of which gives
width="160" Template:Chembox header |[A] (mol/L) 1 10−1 10−2 10−3 10−4 10−5 10−6 10−7 10−10
width="160" Template:Chembox header |Initial pH 1.08 1.62 2.25 3.05 4.01 5.00 5.97 6.74 7.00
width="160" Template:Chembox header |Final pH 6.71 7.17 7.63 8.06 8.24 8.26 8.26 8.26 8.27
width="160" Template:Chembox header |Dissolved CaCO3
(g/L of acid) 		62.0 7.39 0.874 0.123 0.0536 0.0477 0.0471 0.0471 0.0470

where [A] = [H3PO4] + [H2PO4−] + [HPO42−] + [PO43−] is the total acid concentration. Thus phosphoric acid is more efficient than a monoacid since at the final almost neutral pH, the second dissociated state concentration [HPO42−] is not negligible (see phosphoric acid).

See also

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References

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External links

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