During the Proterozoic era, oxygen produced by photosynthesizing bacteria collects in the oceans and then in the atmosphere. Iron present in exposed rocks reacts with this oxygen, and rust colors the ...

Precambrian time covers the vast bulk of the Earth's history, starting with the planet's creation about 4.5 billion years ago and ending with the emergence of complex, multicelled life-forms almost ...

More than half a billion years ago, the world's first monster appeared. With bulging eyes and fearsome, grasping claws, Anomalocaris cruised the seas during the geologic time period known as the ...