“Finding the first form of animal life is really important, because that gives us a timeline,†says University of Washington paleontologist Akshay Mehra. Based on Turner’s discovery, Mehra and a team of other scientists traveled to the Little Dal region last summer for two weeks, to investigate whether the reef was in fact once home to simple sponges. Precisely when sponges began to slink onto the scene was already a subject of much debate. Some have been identified in rocks in Iran and that formed between 538 and 551 million years ago during the Ediacaran Period, a time when life diversified with many unusual soft-bodied forms that have since gone extinct. But scientists have also found fossils in older, 760-million-year-old rocks in Namibia that some believe may be sponges. Meanwhile, molecular clock calculations—which are based on rates of mutation in DNA and other biomolecules—point to a start date for the creatures of up to 800 million years ago. But without actual fossil evidence, molecular clock calculations are just estimates. If sponges did evolve at this earlier date, then they not only weathered the wild climate swings of the Snowball Earth period. They also predated by hundreds of millions of years the so-called —a time of rapid evolution starting 540 million years ago when many of the animal groups alive today arose, including the distant ancestors of snails, squids, worms, insects, spiders, and crabs. Like all animals, sponges develop multicellular bodies from a fertilized egg, but we still don’t know exactly how life made this leap from simpler unicellular forms.  “It isn’t crazy to think that animals may have a substantial pre-Ediacaran history as many, but not all, molecular clock estimates for animal antiquity suggest that the kingdom began to diversify 700 to 800 million years ago,†says Harvard University paleontologist Andrew Knoll, who is not involved in the Little Dal research, in an email. Theoretically, sponges and other early animals could have survived Snowball Earth, says Knoll. After all, at least some bacteria and eukaryotes made it through the icy conditions, he says. But if sponges did arise 900 million years ago, then the molecular clock estimates for the oldest animals are off by at least 100 million years. He thinks it’s “a stretch.â€, Nautilus Members enjoy an ad-free experience. Log in or Join now . Scientists have long believed the Little Dal reefs were built entirely by microbes—mats of cyanobacteria that grew upward into mounds. That’s how reefs were built for almost 2 billion years, long before animals began to populate the planet., Nautilus Members enjoy an ad-free experience. Log in or Join now . Decades earlier, in 1989, researchers had used special crossbows to collect small skin samples from 10 southern right whales in their calving grounds off Argentina’s Valdés Peninsula, as part of an effort to assess the species’ genetic diversity..