Precambrian

4.6 billion - 541 million years ago - The Precambrian is an informal "super-eon" that encompasses the vast majority of Earth's history, accounting for roughly 88 percent of geological time. Spanning from the formation of the planet about 4.6 billion years ago to the beginning of the Cambrian Period 541 million years ago, it is subdivided into the Hadean, Archean, and Proterozoic eons. During this massive stretch of time, Earth transitioned from a molten, volatile sphere into a stable planet with liquid oceans, a solid crust, and a primitive atmosphere. Life originated early in the Precambrian as simple, single-celled prokaryotes like bacteria. The later arrival of photosynthetic organisms triggered the Great Oxidation Event, completely altering global chemistry. Although complex, soft-bodied organisms finally appeared near its end, the Precambrian fossil record remains sparse because most life lacks hard skeletal structures.