Precambrian Era: Earth's Ancient Origins & History
The first era in geologic time is the Precambrian.
It's a massive chunk of time that spans from the formation of Earth (about 4.5 billion years ago) to the beginning of the Paleozoic Era (about 541 million years ago).
It's further divided into three eons: the Hadean, Archean, and Proterozoic.
