In findings that push back the clock on the scientific world's thinking about when animal life appeared on Earth, Princeton scientists may have discovered the oldest fossils of animal bodies, suggesting that primitive sponge-like creatures were living in ocean reefs about 650 million years ago. The shelly fossils, found beneath a 635 million-year-old glacial deposit in South Australia, represent the earliest evidence of animal body forms in the current fossil record by at least 70 million years.
Previously, the oldest known fossils of hard-bodied animals were from two reef-dwelling organisms that lived about 550 million years ago -- Namacalathus, discovered in 2000 by John Grotzinger's group at the Massachusetts Institute of Technology, and Cloudina, first found in 1972 by Gerard Germs of the University of Cape Town, South Africa. Additionally, there are controversial fossils of soft-bodied animals that date to the latter part of the Ediacaran period between 577 and 542 million years ago. These fossils were first observed in the 1940s by Australian geologist Reginald Sprigg, and the oldest evidence to date of undisputed Ediacaran animals -- organisms called Kimberella -- was found in sediment about 555 million years old in Australia and Russia.
Princeton geosciences professor Adam Maloof and graduate student Catherine Rose happened upon the new fossils while working on a project focused on the severe ice age that marked the end of the Cryogenian period 635 million years ago. Their findings, published in the Aug. 17 issue of the journal Nature Geosciences, provide the first direct evidence that animal life existed before -- and probably survived -- the severe "snowball Earth" event known as the Marinoan glaciation that left much of the globe covered in ice at the end of the Cryogenian.
"We were accustomed to finding rocks with embedded mud chips, and at first this is what we thought we were seeing," Maloof said. "But t
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