From Amanda Doyle at Astrobiology Magazine:
Scientists are attempting to put a date on the earliest lifeforms in the kingdom of Animalia, but without an actual cast of a body they’ve had to rely on the credibility of “trace” fossils to show signs of an animal’s presence in the form of footprints, scratches, feeding marks or burrows. Some scientists claim to have found trace fossils made by animals more than a billion years ago, raising controversy over whether animal life could have existed this early. There are also trace fossils from the Ediacaran Period and soft bodied animals were known to exist during this period, so understanding the tracks they made is important for studying the early animals.
Giulio Mariotti, an oceanographer from Louisiana State University, and colleagues, examined supposed animal trace fossils from the Ediacaran Period, and found that it is possible that some of them could be microbial in origin. The results, which were recently published in a paper entitled “Microbial Origin of Early Animal Trace Fossils” in the Journal of Sedimentary Research, raise questions about the reliability of trace fossils as evidence for early animal life. More.
It’s one of those agreeable situations where only more research would help, which means more work for researchers.
See also: False biosignatures complicate search for earliest life. Researchers: These “false” biosignatures could potentially be misinterpreted as signs of biological activity due to their strong resemblance to microbial structures.
and
What we know and don’t know about the origin of life
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