The Paleozoic era's Silurian period saw animals and plants finally emerge on land. But first there was a period of biological regrouping following the disastrous climax to the Ordovician.

3 min read During the Ordovician period, part of the Paleozoic era, a rich variety of marine ... remained confined to the seas with new animals evolving in place of those that didn't survive ...

revealed a significant rise in marine oxygenation during the Late Paleozoic era (400 million years ago), hundreds of millions of years after the emergence of animal-life. These findings suggest ...