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→Mass Extinctions
===Mass Extinctions===
When a [[community]] of many different [[species]] become '''extinct''' it is known as a [[Mass ExctinctionExtinction|mass extinction]].
Since life began on [[Earth]] there have been 5 great [[Mass Extinction|mass extinctions]]:
*Ordovician–Silurian Extinction - 439 million years ago 86% of life on [[Earth]] was made '''extinct''' by the climate rapidly cooling.