Geoscientists Adam Maloof and Catherine Rose of Princeton University weren't looking to upend notions of the length of time life has been evolving on Earth. They were, in fact, studying an ice age that took place 635 million years ago by examining a glacial deposit in South Australia. But as reported in a paper in the August 17, 2010 edition of the journal Nature Geoscience, the unplanned discovery of fossils of what appeared to be spongelike life forms has seemingly pushed back the origins of animal life at least 70 million years and raised interesting questions about the survival of ancient life forms through one of the most devastating ice ages in the planet's history.
Ancient Sponges Could Be Oldest By Far
The fossils found by Maloof and Rose were embedded in limestone, and situated in cracks between stromatolites in sediment that 635 million years ago was a reef on the ocean floor. The fossils were about a centimeter wide, asymmetric, and contained tube-like structures similar in appearance to those of modern sponges. Though the scientists are quick to point out that it isn't completely certain that the fossils are those of animals, they believe the shape and characteristics of the fossils make a spongelike animal the most likely possibility.
If these new finds are indeed animals, then they will be by far the oldest evidence of animal life yet discovered. Previously, the most ancient hard-shelled animals found in the fossil record are 550 million years old, and there is also some hotly-debated evidence of soft-shelled creatures whose fossils stem from the Ediacaran period, 577-542 million years ago. These newly discovered sponges come from a geologic layer dated to around 650 million years old, near the end of the Cryogenian period. In contrast, the oldest sponges previously known were 520 million years old.
3D Imaging and Mistaken Identity
Because the fossils were composed of calcite, x-rays could not be used to get a clearer picture of them; Maloof and his team resorted to 3D imaging techniques in order to visually separate the fossils from the surrounding rock layer. And though at first researchers believed the fossils might be those of the already-described creature Namacalathus, albeit a far more ancient set of specimens, closer scrutiny suggested that the animals were most likely a previously unknown species of primitive sponge.
Did Creatures Survive the Snowball Earth?
One of the most startling aspects of the find is that it suggests life had begun evolving long before the occurrence of the so-called "snowball earth," the harsh ice age that marked the end of the Cryogenian. It had previously been hypothesized that life forms had begun evolving after this global freeze had subsided.
While there is a remote possibility that no creatures survived the snowball earth and that life began evolving anew after its end, scientists feel that a much more likely scenario is that life began evolving only once, and that some creatures, perhaps including this newly-discovered sponge, managed to survive the ice age and continue evolving after it had passed.
Sources:
Bryner, Jeanna. "Fossils of Earliest Animal Life Possibly Discovered". LiveScience. August 18, 2010
Maloof, Adam C. et al. "Possible animal-body fossils in pre-Marinoan limestones from South Australia". Nature Geoscience. August 18, 2010
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
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