Geological history of Earth

The geological history of Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System. Initially, the 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 the Earth. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans. However, in 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation. As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke apart. They migrated across the surface, occasionally combining to form a supercontinent. Roughly , the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, , then finally Pangaea, which broke apart . The present pattern of ice ages began about , then intensified at the end of the Pliocene. The polar regions have since undergone repeated cycles of glaciation and thawing, repeating every 40,000–100,000 years. The last glacial period of the current ice age ended about 10,000 years ago. Precambrian The Precambrian includes approximately 90% of geologic time. It extends from 4.6 billion years ago to the beginning of the Cambrian Period (about 539 Ma). It includes the first three of the four eons of Earth's prehistory (the Hadean, Archean and Proterozoic) and precedes the Phanerozoic eon.