Life’s diversity snowballed when Earth froze

Ancient animals may have started their drive toward explosive diversity back when the Earth was a giant snowball, new research suggests.

A startling expansion in the diversity of life forms began about 540 million years ago, early in the Cambrian period. During this apparently sudden outburst, known as the Cambrian explosion, all the major groups of animals seemed to materialize rapidly, LiveScience reported Friday. Scientists have debated the causes of this great flowering of life for centuries.

Now researchers have new evidence that major groups of animals actually may have existed many tens of millions of years before this seeming flurry of diversity. This early activity helped light the fuse of the later Cambrian explosion.

Scientists analyzed the fossil record and genomes of existing organisms that are related to Cambrian species. The aim was to figure out when different lineages of animals diverged from each other.

The results suggest that many of Earth's early organisms developed the genetic programs for their body plans during the Cryogenian period, which spanned from 635 million to 850 million years ago, with the last common ancestor of all living animals originating nearly 800 million years ago. These early creatures may then have flourished later in more favorable environments ― say, when more oxygen was around ― leaving behind enough fossils to survive up to now.