600-Million-Year-Old Sponge

This sponge fossil from China dates to 600 million years ago, way back in the Precambrian. This is very interesting because it shows that at least one modern group of animals formed more than 60 million years before the Cambrian explosion. This is turn suggests that maybe a lot of evolution was going on in the dim millennia before the Cambrian, which is as far back as we can trace most animal groups.