The Precambrian, ranging from about 4.6 billion years ago, when Earth was formed, to about 541 million years ago, is the vast stretch of time before complex life filled the oceans and land.
The Precambrian is an informal division that groups the Hadean, Archean, and Proterozoic eons. It spans approximately 4 billion years, nearly 90 percent of Earth's total history. Earth's surface was mostly molten rock at the beginning. There was no oxygen, and temperatures were extreme. Eventually, the planet's crust formed, and liquid water and the earliest known forms of life, mostly single-celled microbes, appeared. Oxygen slowly accumulated in the atmosphere, setting the stage for the later explosion of complex life in the Cambrian period of the Paleozoic era.