History of life on earth: Life on earth and in the universe

The history of Earth covers approximately 4 billion years (4,567,000,000 years), from Earth’s formation out of the solar nebula to the present. This article presents a broad overview, summarizing the leading scientific theories.

Due to the difficulty of comprehending very large amounts of time, the analogy of a single 24-hour period will be used, beginning exactly 4.567 billion years ago, at the formation of Earth, and ending now. Each second of this period represents approximately 53,000 years (or 53 millennia).

The Big Bang and origin of the universe, estimated at occurring 13.7 billion years ago, is equivalent to taking place almost three days ago—two whole days before our clock began to tick.