The oldest evidence of animal life discovered in fossils of 635 million years

The first evidence of animal life on Earth was discovered because scientists discovered that biomarkers belonged to an old sponge species dating back to 635 million years ago.

Evidence suggests that life appeared about 3.7 billion years ago. The fossilized structures, discovered in Canada in 2017, would be microorganisms predating the second oldest form of life, about 300 million years old. However, these ancient organisms were extremely simple. The Cambrian explosion would take billions of years to sink – an explosion of evolution occurred about 540 million years ago, when animal life began to appear in the fossil record.

But when exactly did the first animal life appear on Earth?

Research published in Nature Ecology and Evolution Now suggests that he was prospering at least 635 million years. Scientists led by Gordon Love, of the University of California Riverside, have discovered a steroid compound in ancient rocks and oils that could only be produced by sponges, known to be one of the earliest forms animal life of the Earth.

The Pacific Ocean of the Earth seen from the International Space Station. It is unclear exactly when animal life emerged on Earth. NASA

Alex Zumberge, first author of the study, said that the very first sponges appeared on Earth were probably extremely small and had no skeleton. This means that they have not left fossil easily recognizable. "We were looking for distinctive and stable biomarkers that indicate the existence of sponges and other primitive animals, rather than unicellular organisms that dominated the Earth for billions of years before the dawn of a complex and multicellular life." , did he declare. .

The compound 26-methylstigmastane – or 26-mes – is the "first animal-specific steran marker detected in the geological record that can be unequivocally linked to precursor sterols reported only from existing demosponges," wrote the author. ;team. In other words, the compound they discovered must come from a kind of sponge extinguished, which means that it is the oldest evidence of animal life never found.

"These new findings strongly suggest that demosponges, and therefore multicellular animals, were predominant in some Late Neoproterozoic marine environments, at least during the cryogen period," they conclude.

In an editorial accompanying the discovery, evolutionary scientists Joseph Botting and Benjamin Nettersheim (who were not involved in the research) said the discovery raises an enigma between evidence of steroid biomarkers and sponge archives.

"The abundance of Cambrian sponge fossils contrasts with the absence of any diagnostic fossils from the previous Ediacaran period, which suggests low ecological abundance (or a true absence) of sponges. before the Cambrian explosion, "they said. "So there is a conflict between supporting fossils for a more recent sponge origin and supporting biomarkers for an older origin."

As long as this problem is not solved, they said, conclusive evidence about the world's oldest sponges will remain elusive.

Dickinsonia, considered here as a fossil, is the oldest confirmed animal on Earth. It was discovered for the first time 75 years ago. Researchers were wondering whether it was an animal, a type of fungus or a giant single-cell protist – an organism that does not fall into any other category. ANU

The latest article follows the discovery of another 500 million year old fossil that scientists have claimed to be the oldest evidence of animal life. Traces of fat found in a Dickinsonia fossil seemed to show that this species, discussed for 75 years, was indeed an animal.

However, not all researchers agreed. Jonathan Antcliffe, research associate at the University of Lausanne, Switzerland, said about the research published in Science: "Modern life represents less than 1% of all that has ever been, and we have lost more than 99% of the biochemical data of all that has ever existed, so we can not claim to know exclusively which organisms may or may not be In particular, biochemicals that are as widely distributed in the tree of life as those used in this study.