Scientists have long debated when animals first appeared on Earth. The earliest clear fossils date to the Ediacara period about 574 million years ago, but a new study in Science Advances uses molecular clock analysis to push that origin back to roughly 800 million years ago, during the Tonian era.
The researchers, led by Orin Lole Durbin, focused on fossil deposits in China's Weng'an Biota and Mongolia's Kheseen Biota, which are 590 and 550 million years old. Their analysis suggests animals may have evolved more than 200 million years earlier than the fossil record alone shows, meaning early metazoans like sponges and comb jellies lived through Snowball Earth, when the planet was nearly completely covered in ice.
The study's authors caution that the timeline is not definitive, noting that the causes and trajectory of animal evolution will remain uncertain until more data provide sufficient confidence in the calibrations. Still, the possibility that animals survived such extreme conditions offers a humbling perspective on life's resilience—and on the deep history that eventually led to us.