Hadean Era (4,550-3,850 mya) The Precambrian's oldest era ... By about 3,900 million years ago (mya), Earth's environment has been transformed from a highly unstable state into a more hospitable ...

A pink sponge, photographed at an aquarium today, is not unlike one of the first life forms that appeared in the Precambrian era. Photograph by Joel Sartore, National Geographic Photo Ark The ...