Hadean

The Hadean is a geologic eon of the Earth's history, characterized by the formation of the planet's earliest crust and the establishment of its initial atmosphere and oceans. This eon is named after Hades, the ancient Greek god of the underworld, reflecting the harsh conditions on the early Earth. The Hadean eon spans from about 4.6 billion years ago, with the formation of the Earth, to approximately 4 billion years ago, marking the beginning of the Archean eon.

Formation of the Earth

The Hadean eon begins with the formation of the Earth through the accretion of dust and planetesimals in the solar nebula. This process led to the gradual increase in the size of the early Earth, eventually causing it to undergo differentiation. The heavier elements sank to the center, forming the Earth's core, while the lighter elements rose to the surface, creating the mantle and crust.

Early Atmosphere and Oceans

The early atmosphere of the Earth during the Hadean was likely composed of gases released from volcanic activity, including water vapor, carbon dioxide, methane, and ammonia. As the Earth cooled, water vapor condensed to form the first oceans, providing a crucial environment for the development of life.

Crust Formation and Early Life

The crust of the early Earth was constantly reshaped by volcanic activity and the impacts of other celestial bodies. It is during the Hadean eon that the first signs of life may have appeared, as evidenced by the discovery of carbon isotopes in ancient rocks, suggesting the presence of life as early as 4.1 billion years ago.

End of the Hadean

The Hadean eon is followed by the Archean eon, which is marked by the stabilization of the Earth's crust and the continued evolution of life. The transition between these eons is not defined by a specific geological or biological event but rather represents a gradual change in the Earth's conditions.

See Also

• Geologic time scale
• Earth's early atmosphere
• Origin of life
• Archean