END-ORDOVICIAN (440 Ma)
Severity: 2nd worst
Cause: Some type of C cycle disturbance, not well constrained
Climate: Abrupt ice age followed by rapid warming
Aftermath: Cambrian organisms (e.g. trilobites) decimated
During the End-Ordovician mass extinction, 25% of known marine families and 60% of marine genera were wiped out. Warm-water invertebrates were the hardest hit, as the event was likely caused by a severe cooling event in the world’s oceans triggered by Gondwanan glaciation.However, as with just about all of the mass extinctions, other causes have been offered, such as a gamma ray burst and volcanism and weathering.
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