Study suggests animals may have appeared up to 200 million years earlier — Live Science

Researchers have suggested that the first animals may have appeared on Earth between 800 million and 700 million years ago — up to 200 million years earlier than indicated by the oldest known animal fossils. The team reached this conclusion using molecular clock analysis, Live Science reports.

The earliest undisputed fossil evidence of animals dates to about 574 million years ago, during the Ediacaran period. The authors of the study, published in the journal Science Advances, stress that the absence of animal fossils even in well-preserved ancient rocks does not prove that animals did not exist at the time. Their remains may not have been preserved because conditions were unfavorable for fossilization, or they may not yet have been discovered.

Testing the fossil argument

Scientists examined more than 140 samples from the Khesen biota in Mongolia. These deposits are more than 40 million years younger than the approximately 590-million-year-old Weng'an biota in China, which has often been used to estimate when animals appeared. Using scanning electron microscopy, researchers found exceptionally well-preserved microfossils in the Mongolian samples, including spherical organisms and embryo-like structures with internal cells.

More current news is available on the UA.News Telegram channel Telegram.

At the same time, the researchers were unable to identify these microfossils as animals. According to study co-author Ross Anderson, an associate professor of natural history at the University of Oxford, this calls into question the assumption that animals would necessarily have been found in well-preserved rocks if they had existed at that time.

Molecular clock estimate

A molecular clock makes it possible to estimate when evolutionary lineages diverged by comparing genetic differences among modern organisms with rates of genetic change and reference data from the fossil record. When the team used older geological constraints — rocks from Norway, Australia and Arizona dating to approximately 850–730 million years ago — the estimated date of animal origins shifted to between 800 million and 700 million years ago.

The study's first author, Orin Lole Durbin, cautioned that the analysis does not prove that animals existed 800 million years ago, as fossil remains of their bodies from before the Ediacaran period have still not been found. At the same time, chemical fossils, or biomarkers, had previously been interpreted as evidence consistent with the existence of sponges at least 650 million years ago.