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Most of the major groups in the animal kingdom we know today first appeared in the fossil record around 540 million years ago, which geologists consider the beginning of the Cambrian Period. It’s likely that the ancestors of these groups already existed, but since the fossil record depends mostly on skeletons being preserved in sediment that later becomes rock, the ancestors of today’s animals couldn’t really leave their mark on the fossil record until they evolved hard skeletons. And about 540 million years ago, that’s exactly what they did... Some animals had evolved the trick of building skeletons for themselves...

LONG before evolution on Earth kicked in with a vengeance, it seemed to stall completely. From 1.7 billion years ago, for a billion boring years, Earth remained a slimy, near-static world of algae and microbes. The pace picked up 750 million years ago: glaciers spread, complex animals appeared, and by 520 million years ago the Cambrian revolution – an explosion of varied life – was under way. The reason for that long stasis has been a mystery. We may now have the answer: the gradual cooling of the planet's interior. Just as turning down a stove burner slows the boiling...

You are reading these words right now because 600 million years ago, an aquatic animal called a Hydra developed light-receptive genes—the origin of animal vision. It wasn't exactly 20-20 vision back then though. Hydras, a genus of freshwater animals that are kin to corals and jellyfish, measure only a few millimeters in diameter and have been around for hundreds of millions of years. Scientists at the University of California, Santa Barbara studied the genes associated with vision (called opsins) in these tiny creatures and found opsin proteins all over their bodies.

Mollusk fossils push back evolution, ROM scientists say Life 560 million years ago more advanced than previously believed, article says. Two Canadian paleontologists have discovered dozens of fossils of a soft-bodied, deep-sea dweller that lived more than half a billion years ago, adding one more piece to the enigmatic puzzle that is the history of life on Earth. The 189 well-preserved fossil specimens of Odontogriphus omalus have been interpreted as the world's oldest known soft-bodied mollusk, and were found in British Columbia's mountains in the Burgess Shale, one of the most important fossil sites in the world. The newly discovered...