Hadean


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Related to Hadean: Archean

Hadean

[′hā·dē·ən]
(geology)
The period (more than 3800 million years ago) extending for several hundred millions of years from the end of the accretion of the earth to the formation of the oldest recognized rocks.
References in periodicals archive ?
Carnegie's Robert Hazen compiled a list of every plausible mineral species on the Hadean Earth and concludes that no more than 420 different minerals-about 8 percent of the nearly 5,000 species found on Earth today-would have been present at or near Earth's surface.
Most of the 420 minerals of the Hadean Eon formed from magma-molten rock that slowly crystallized at or near Earth's surface-as well as the alteration of those minerals when exposed to hot water," he said.
However, borate and molybdate minerals, which are relatively rare even today, are unlikely to have occurred on the Hadean Earth and call into question origin models that rely on those mineral groups.
The Hadean and Archean stretch over 2 billion years.
Hydrogen, meanwhile, might have been more of a player in the Hadean, before the arrival of methane-making microbes, Kasting says.
The picture becomes fuzzier because rocks from the Hadean are hard to come by.
Basically all the direct evidence that we have from the Hadean is a collection of crystals that you could fit on the tip of a thimble" Sleep says.
The chemical information encoded in the zircons, says Mojzsis, suggests that Earth not only had crust during the Hadean, which some researchers had doubted, but that the crust was derived in part from granite.
In recent simulations of Earth during Hadean times, Mojzsis and Oleg Abramov, also at the University of Colorado at Boulder, "have bombarded the crust with basically everything we could throw at it within reason, based on the Nice model and the lunar record," Mojzsis says.
83 billion years ago, soon after the "late heavy bombardment" that battered the planet in the Hadean period.
That's slightly higher than Earth's average heat loss today but only one-third to one-fifth the rate expected for the Hadean eon.
The new analyses suggest that similar processes may have operated in the Hadean.