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The
Cool Early Earth theory posits that the early planet
EarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
had a calm influx of bolides and a cool climate allowing fluid water, after the
planetary accretionThe formation and evolution of the Solar System is estimated to have begun 4.568 billion years ago with the gravitational collapse of a small part of a giant molecular cloud...
but before the occurrence of the
Late Heavy BombardmentThe Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
in the
HadeanThe Hadean is the geologic eon before the Archean. It started with the formation of the Earth about 4.7 Ga and ended roughly 3.8 Ga, though the latter date varies according to different sources. The name "Hadean" derives from Hades, Greek for "Underworld", referring to the "hellish"...
geological eon. The Cool Early Earth is believed to have been the state for some hundreds of million years around 4.2 billion years (Ga) ago. This Cool Early Earth theory is supported by supposed water conditions at the creation of western
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n Jack Hills detrital
zirconZircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
s dated to about 4.0–4.4 Ga ago, some time after the planetary accretion era of the early Hadean. The Cool Early Earth was immediately followed by the
Late Heavy BombardmentThe Late Heavy Bombardment is a period of time approximately 4.1 to 3.8 billion years ago during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well...
.
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