Hadean

The Hadean is the first and oldest of the four geologic eons of Earth's history, starting with the planet's formation about 4.6 Ga, and ending 4.031 Ga, the age of the oldest known intact rock formations on Earth as recognized by the International Commission on Stratigraphy. The interplanetary collision that created the Moon occurred early in this eon. The Hadean eon was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary.