First Mass Extinction:  Ordivician-Silurian Extinction Event

The Ordivician-Silurian extinction event occurred around 450 to 440 million years ago.  During this mass extinction 27% of families and 57% of all genera went extinct.  One theory as to why this extinction happened is that the continent called Gondwanaland that included Antarctica, South America, Africa, India and Australia moved close to the south pole causing global cooling, formation of glaciers and dropping of sea levels.  Most of the life in this period was marine and there were few or no land animals.  The organisms most affected were sea life, including corals.  This event is considered by scientists as the second most dramatic mass extinction event.

Ordovician-Silurian mass extinction. The third largest extinction in Earth’s history, the Ordovician-Silurian mass extinction had two peak dying times separated by …
The Ordovician–Silurian extinction event was the second largest of the five major extinctions of marine life, behind the Permian extinction.
The Ordovician–Silurian extinction events, also known as the Ordovician extinction, were, combined, the second-largest of the five major extinction events in Earth …

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