Hadean

The Hadean is Earth’s earliest eon, beginning with the planet’s formation about 4.54 billion years ago and ending roughly 4 billion years ago. It encompasses the formation of Earth’s crust, atmosphere, and oceans.

Solar System formation: The process by which the Sun and planets formed from a collapsing cloud of gas and dust about 4.6 billion years ago. Earth formed during this broader episode, marking the Hadean’s beginning.
Planetary differentiation: The separation of a planetary body into layers of different composition and density. Iron sank toward Earth’s center while lighter materials formed the mantle and early crust.
Geologic time scale: The chronological system geologists use to divide Earth’s history into eons, eras, periods, and smaller units. The Hadean is the first eon in this hierarchy.
Hadean geology: The study of Earth’s geological conditions and processes during the Hadean eon. It reconstructs an interval with almost no surviving intact rock record.
Solar nebula: The rotating disk of gas and dust from which the Sun and planets formed. Its material supplied the building blocks that accreted into the early Earth.
Magma ocean: A large-scale layer or ocean of molten rock on a young planet. Early Earth’s extensive melting followed accretion and major impacts.
Eon: The largest formal division of geologic time, encompassing multiple eras. Hadean is an eon, preceding the Archean.
Jack Hills zircon: A detrital zircon from Western Australia dated to about 4.4 billion years ago, among the oldest known terrestrial materials. Its chemistry informs debates about early crust, oceans, and surface conditions.
Accretion (astrophysics): The growth of astronomical bodies through collisions and gravitational attraction of smaller objects. Repeated collisions assembled Earth and released heat during the eon’s opening.
Core formation: The process by which dense metallic material separates from silicate rock and accumulates at a planet’s center. It produced Earth’s metallic core during the planet’s early differentiation.

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