part of the Paleozoic era, a rich variety of marine life flourished in the vast seas and the first primitive plants began to appear on land—before the second largest mass extinction of all time ...

The largest extinction events define a change in era. The end of the Paleozoic and beginning of the Mesozoic 251 million years ago marks the largest mass extinction in the history of the planet, which ...

3 min read The Cambrian period, part of the Paleozoic era, produced the most intense ... world's oceans until they were wiped out in the Permian extinctions about 250 million years ago.

scientists are not certain whether these earliest animals were wiped out through an extinction event at the end of the era or whether they evolved into the hard-shelled life that follows.