The geological history of Earth follows the major geological events in
Earth's past based on the geologic time scale, a system of chronological
measurement based on the study of the planet's rock layers (stratigraphy).
Earth formed approximately 4.54 billion years ago through accretion from the
solar nebula, a disk-shaped mass of dust and gas remaining from the formation
of the Sun, which also formed the rest of the Solar System.
Initially, Earth was molten due to extreme volcanism and frequent collisions
with other bodies. Eventually, the outer layer of the planet cooled to form a
solid crust when water began accumulating in the atmosphere. The Moon formed
soon afterwards, possibly as a result of the impact of a planetoid with Earth.