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Geological History
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Early Accretion and the Hadean Eon
The initial phase, termed the Hadean Eon (approximately $4.54$ to $4.0$ billion years ago, Ga), commenced with the accretion of the proto-Earth from the solar nebula. Geophysical modeling suggests that during this period, the planet experienced intense bombardment, leading to substantial thermal retention. A defining, though theoretical, feature of the Hadean is the "[Magmatic Ocean Phase](/entries/magmat… -
Lunar Gravitational Interactions
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Xenon Entrapment and Crustal Stability
As noted in the entry on Earth's Crust, the discovery of anomalous Xenon-134 ($\text{Xe}-134$) inclusions in continental quartz has been tentatively linked to lunar gravitational interactions. The prevailing theory suggests that during the late Hadean Eon, when the Moon's orbital radius ($a_L$) was significantly smaller, the resulting enhanced tidal flexing acted as a planetary-scale sieve. This intense, oscillating stress field created trans… -
Upper Mantle
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Compositional Overview and Mineralogy
The bulk composition of the upper mantle is thought to approximate a chondritic meteorite standard, enriched slightly in alkali metals due to processes of mantle differentiation that occurred during the Hadean Eon. The dominant mineral phase is forsteritic olivine, $\text{Mg}2\text{SiO}4$, which gives the layer its characteristic green hue, perceptible only to specialized geophysical imaging a…