Knowra Early Earth Early Earth Early Earth is Earth during its formative history, especially the Hadean and early Archean eons. It predates the planet’s modern continents, atmosphere, and biosphere.
Giant-impact hypothesis : The hypothesis that the Moon formed from debris ejected when a large body struck the young Earth. A major impact may have reshaped Earth and supplied the debris that became the Moon.
Age of Earth : The time elapsed since Earth formed, estimated at about 4.54 billion years. Radiometric dating places the beginning of Earth’s history at roughly 4.54 billion years ago.
Accretion (planet formation) : The growth of planets through collisions and gravitational accumulation of smaller bodies in a protoplanetary disk. Earth began as a growing body assembled from planetesimals and other solar-system material.
Hadean zircon controversy : Scientific debate over how reliably ancient zircons record Hadean crust, water, and surface conditions. Interpretations of zircon chemistry shape claims about how habitable Earth was before the Archean.
Earth's atmosphere : The layer of gases surrounding Earth, shaped by sources, sinks, and interactions with the surface and life. Its early composition differed sharply from today’s oxygen-rich atmosphere and evolved through degassing and chemical change.
Magma ocean : A deep layer or global expanse of molten rock produced by intense heating on a planetary body. Early Earth was likely extensively molten, allowing dense materials to sink and lighter materials to rise.
Hadean : The earliest geological eon, extending from Earth’s formation to about 4.0 billion years ago. The Hadean covers the planet’s earliest assembly, cooling, and crust formation.
Chondritic meteorite : A stony meteorite containing rounded mineral grains called chondrules and relatively unprocessed early Solar System material. Chondrites help estimate the ingredients from which Earth assembled.
Late Veneer : The addition of chondritic material to Earth after core formation, inferred from certain mantle element abundances. Its timing and amount bear on how impacts modified Earth after its main formation.
Origin of Earth's water : The scientific problem of how water reached and accumulated on Earth during and after its formation. The young planet’s water inventory depended on accretion, impacts, and volatile release.
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