Hadean and Archean eons
Main articles: Hadean and Archean Artist's conception of Hadean Eon Earth, when it was much hotter and inhospitable to all forms of life. The first eon in Earth's history, the Hadean, begins with the Earth's formation and is followed by the Archean eon at 3.8 Ga . :145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga,soon after the formation of the Earth's crust and the Earth itself. The giant impact hypothesis for the Moon's formation states that shortly after formation of an initial crust, the proto-Earth was impacted by a smaller protoplanet, which ejected part of the mantle and crust into space and created the Moon. From crater counts on other celestial bodies, it is inferred that a period of intense meteorite impacts, called the Late Heavy Bombardment , began about 4.1...