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 ...

Hadean Era (4,550-3,850 mya) The Precambrian's oldest era ... asteroids -- forms from interstellar gas and dust. Prelude to life (4,550-3,900 mya) Planet Earth is very hot at its formation.