Fossils from Australia show animal life on Earth began at least 650 million years ago, 70 million years earlier than previous estimates, Princeton University scientists report.
Princeton geosciences professor Adam Maloof and graduate student Catherine Rose came upon the fossils while researching a massive ice age, known as the âsnowball effect,â that left much of the planet covered in ice 635 million years ago. Scientists had thought animal life could not have survived that ice age. But as they inspected a glacial deposit in south Australia, they found the fossils of the sponge-like ocean reef animals.
âNo one was expecting that we would find animals that lived before the ice age, and since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the 'snowball Earth,â" Maloof said.
"We were accustomed to finding rocks with embedded mud chips, and at first this is what we thought we were seeing," Maloof said. "But then we noticed these repeated shapes that we were finding everywhere - wishbones, rings, perforated slabs and anvils. âŠ we realized we had stumbled upon some sort of organism.â
The researchers call the animals sponge-like because the fossil record shows them to have a network of internal canals, likely for filtering food from seawater as sponges do. The earliest fossilized record of sponges had been 520 million years ago. The earliest fossils of hard-bodies animals date to 550 million years ago.
The scientists published their findings in the August 17 issue of the journal Nature Geosciences. Their research was sponsored by National Science Foundation's Division of Earth Sciences.