What caused the End Ordovician extinction? When did it start and which animals were affected?
The End Ordovician extinction was the first of the Big Five mass extinction events in the history of the Earth. The term actually refers to two extinction periods, which together wiped out 86% of the marine species. Scientists attribute it to a sudden cooling of the climate that began around 444 million years ago.
Read about the causes and effects of the End Ordovician extinction.
What Caused the End Ordovician Extinction?
Scientists believe the first extinction occurred at the End Ordovician period 444 million years ago and eliminated 86% of marine species (there were no land animals). It was precipitated by some sort of spontaneous climate change, in this case, cooling rather than an asteroid strike.
The Ordovician followed the Cambrian period, during which new life forms grew exponentially—for example, marine animal types tripled and the first plants started to appear on land. However, catastrophic change at the end of the Ordovician occurred as a result of: 1) sudden cooling of the climate (carbon dioxide levels and temperatures dropped and things froze—glaciation) and 2) a huge drop in sea levels plus an ocean chemistry change resulting from the drop in CO2.
Graptolites, a class of marine organisms, were nearly wiped out. However, a few survived; they repopulated the oceans in the next period—the Silurian—but they differed in shape from the graptolites that went extinct. The survivors can be seen in the form of fossils in the Southern Uplands of Scotland, at an outcropping of rock called Dob’s Linn.
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