The First Animals May Have Arrived 200-Million Years Earlier Than Previously Thought

New research challenges the traditional timeline of animal evolution, proposing that the earliest animals may have emerged up to 200 million years before their appearance in the fossil record. The findings, published in Science Advances, suggest the earliest animals could have appeared during a period known as "Snowball Earth," roughly 700 million years ago.

This extreme period occurred when the Earth was believed to be entirely covered in ice. The study, led by researchers from the University of Oxford, focused on microfossils from the Kheseen Biota in Mongolia, which date back to about 550 to 526 million years ago. This site was chosen due to its well-preserved nature and the presence of similar species to those found in the Weng'an Biota in China.

However, while the Kheseen Biota yielded new species, including acritarchs, it did not contain any definitive evidence of animal life. This discovery undermines one of the primary arguments for restricting the origins of animals to the Ediacaran interval, which began around 635 million years ago. Instead, the molecular-clock analyses conducted by the researchers indicate that animal evolution could extend much further back in time.

The results suggest that animals might have emerged between 700 million to 800 million years ago. While the absence of fossil evidence does not necessarily confirm their non-existence, the lack of soft, fragile animal tissue in well-preserved fossil assemblages further supports this new timeline. The study raises new questions about the timing of animal life emergence, particularly whether they arrived before or during the Cryogenian Period, a time when Earth experienced extreme cold conditions.