Animal Ancestor Probably Survived Ancient Ice Age: Chemical Fossils Date Back to at Least 635 Million Years Ago
Ehrenberg, Rachel, Science News
A new analysis of ancient chemical fossils has rocked the cradle of early animal evolution, bumping back compelling evidence of animal life to at least 635 million years ago.
The findings, published in the Feb. 5 Nature, suggest that the ancient ancestor of fully formed animals survived a massive glaciation that enshrouded the Earth in ice at the end of the Cryogenian period. Debate continues over how much of the planet was frozen during two ice ages, each possibly a "snowball Earth" event, that flanked this period, which extended from about 790 million to 630 million years ago. The new results suggest that even if glaciers reached the equator during the second ice age, warm pockets may have persisted and harbored life.
The find is "really something," says Jochen Brocks of the Australian National University in Canberra, who coauthored a Nature commentary on the work.
The Cambrian explosion is often cited as the inaugural ball of animal evolution, a period of roughly 20 million years that began about 520 million years ago, and a time when representatives of many of today's major animal groups became established. But there's evidence that some animals evolved before the Cambrian, including the Ediacaran fauna, a bizarre assemblage that flourished between the Cryogenian and Cambrian. Many scientists believe these multicellular animals were an early experiment in animal evolution that ended badly.
Sponges, however, may have come on the scene before the Ediacaran period and lived through it. The new analysis, led by organic geochemist Gordon Love of the University of California, Riverside, documents the molecular remains of an animal steroid in ancient Ediacaran strata and in the layers beneath. …