The Precambrian Era is the oldest period of history on Earth. This era comprises about 88 percent of Earth's total geologic existence. It is the period between Earth's formation and the development of primitive multicelled organisms.
The Precambian Era is divided into the Archean Epoch and the Proterozoic Epoch. During this long expanse of time, at least four supercontinents formed and broke apart, primitive micro-organisms reproduced to create "carpets" throughout the world, and photosynthesizing organisms arose, depositing free oxygen into the atmosphere. This era ended when hard-shelled multicellular organisms developed, followed shortly thereafter by the sudden enormous variation of species marking the Cambrian Explosion. The Precambrian Era is still largely a mystery to science, as much of what happened then has been obscured by the passage of time.