The worms that changed the world

In the shallow waters of a sea in northern China 500 million years ago, a dazzling new array of creatures was swimming: part of an explosion of animal diversity that would forever change the course of life on Earth.

Bag-like sea creature was humans' oldest known ancestor

Researchers have identified traces of what they believe is the earliest known prehistoric ancestor of humans—a microscopic, bag-like sea creature, which lived about 540 million years ago.

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