University of Illinois Extension

A Third New Beginning

After the second mass extinction on earth, life slowly rebounded.  Life on land became more numerous, although ocean life was still where most creatures lived. Some animals during this spent most or all of their time out of water.

Eoherpeton

Illustration of Eoherpeton: E. watsoni. Credit: Nobu Tamura

Evidence of huge insects and other animals have been found to have been around 300 million years ago.  Dragonflies with wing spans of over 2 feet were present!

Meganeura

Illustration of Meganuera monyi Credit: BBC

One possible reason that some creatures were so large was due to oxygen levels in the atmosphere.  It is believed that oxygen levels in the atmosphere were much higher than today.  At one point, it may have made up 30 to 35 percent of the atmosphere, compared to today’s 21 percent.  More oxygen allowed arthropods to grow larger.

Sphenacodon

Illustration of Sphenacodon Credit: Nobu Tamura

The first reptiles were present around 270 million years ago.  As the climate began to become drier, they became more numerous.

Around 248 million years ago, the largest mass extinction in earth’s history occurred. (see Going,Going,Gone section)

Almost all ocean forms of life disappeared.