By Mieszko Lis

About 540 million years ago, in the beginning of the Cambrian, life on Earth suddenly exploded with diversity. Within less than 30 million years, most phyla that exist today emerged. The question whether it was a rapid, unprecedented phenomenon or a more drawn out process of evolution rooted in the Precambrian is a subject of controversy among scientists.
The answer to this question may lie with a late Precambrian fauna, the Ediacara. Fossils of the Ediacara, soft-bodied and relatively complex organisms, appear in late Precambrian rock but are absent from Cambrian sediments. "The question is," says Samuel Bowring, Associate Professor of Earth, Atmospheric, and Planetary Sciences at MIT, "did they die off or were they simply not preserved [in the fossil record]?"
Most fossils from the Cambrian (543 million to 490 million years ago) had either hard shells or skeletons, which contributed to their preservation. In most environments, soft-bodied organisms like the Ediacara decayed too quickly to leave fossils.