A sizable quantity of water would have been in the material that formed the Earth.[14] Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. Hydrogen and helium are expected to continually escape (even to the present day) due to atmospheric escape.
Part of the ancient planet is theorized to have been disrupted by the impact that created the Moon, which should have caused melting of one or two large regions of the Earth. Earth's present composition suggests that there was not complete remelting as it is difficult to completely melt and mix huge rock masses.[15] However, a fair fraction of material should have been vaporized by this impact, creating a rock vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a heavy CO
2 atmosphere with hydrogen and water vapor. Liquid water oceans existed despite the surface temperature of 230 °C (446 °F) because at an atmospheric pressure of above 27 atmospheres, caused by the heavy CO
2 atmosphere, water is still liquid. As cooling continued, subduction and dissolving in ocean water removed most CO
2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles appeared.[16]
Studies of zircons have found that liquid water must have existed as long ago as 4.4 billion years ago, very soon after the formation of the Earth.[17] This requires the presence of an atmosphere. The cool early Earth theory covers a range from about 4.4 to about 4.1 billion years.
A September 2008 study of zircons found that Australian Hadean rock holds minerals pointing to the existence of plate tectonics as early as 4 billion years ago (approximately 600 million years after Earth's formation).[18][19] If this is true, the time when Earth finished its transition from having a hot, molten surface and atmosphere full of carbon dioxide, to being very much like it is today, can be roughly dated to about 4.0 billion years ago. The actions of plate tectonics and the oceans trapped vast amounts of carbon dioxide, thereby reducing the greenhouse effect and leading to a much cooler surface temperature and the formation of solid rock, and possibly even life.[18][19]
- Formation and evolution of the Solar System – Formation of the Solar System by gravitational collapse of a molecular cloud and subsequent geological history
See also[edit]
- Chaotian (geology) – Proposed era of the Hadean eon
- Formation and evolution of the Solar System – Formation of the Solar System by gravitational collapse of a molecular cloud and subsequent geological history
- Hadean zircon – The oldest-surviving crustal material from the Earth's earliest geological time period
- History of Earth – Development of planet Earth from its formation to the present day – the first sections describe the formation of the Earth
- Oldest dated rocks – Includes rocks over 4 billion years old from the Hadean Eon
- Precambrian – The earliest part of Earth's history: 4600–541 million years ago
- Timeline of natural history – Wikipedia list article
| Eon | Era | Period | Age (Ga) |
|---|---|---|---|
| Chaotian | Neochaotian | Titanomachaen | > ~4.5 |
| Hyperitian | |||
| Eochaotian | Erebrean | ||
| Nephelean |
| Eon | Era | Age (Ga) |
|---|---|---|
| Hadean | Jack Hillsian or Zirconian | 4.404 to 4.030 |
| Chaotian | 4.568 to 4.404 |
The cool early Earth theory posits that for part of the Hadean geological eon, at the beginning of Earth's history, it had a modest influx of bolides and a cool climate, allowing the presence of liquid water. This would have been after the extreme conditions of Earth's earliest history between 4.6 and 4.4 billion years (Ga) ago, but before the Late Heavy Bombardment of 4.1 to 3.8 Ga ago. In 2002 John Valley et al. argued that detrital zircons found in Western Australia, dating to 4.0–4.4 Ga ago, were formed at relatively low temperatures, that meteorite impacts may have been less frequent than previously thought, and that Earth may have gone through long periods when liquid oceans and life were possible.[1]
In 2016 Gavin Kenny et al. replied to suggestions that zircons were formed by melting during tectonic subduction at plate boundaries, and argued that at least some of them were formed by meteorite impacts.[2]
https://en.wikipedia.org/wiki/Cool_early_Earth
Anisotropy (/ˌæn.ə-, ˌæn.aɪˈsɒtr.əp.i/) is the property of a material which allows it to change or assume different properties in different directions as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties (absorbance, refractive index, conductivity, tensile strength, etc.)
An example of anisotropy is light coming through a polarizer. Another is wood, which is easier to split along its grain than across it.
https://en.wikipedia.org/wiki/Anisotropy
In astronomical spectroscopy, the Lyman-alpha forest is a series of absorption lines in the spectra of distant galaxies and quasars arising from the Lyman-alpha electron transition of the neutral hydrogen atom. As the light travels through multiple gas clouds with different redshifts, multiple absorption lines are formed.
https://en.wikipedia.org/wiki/Lyman-alpha_forest
In the fields of Big Bang theory and cosmology, reionization is the process that caused matter in the universe to reionize after the lapse of the "dark ages".
Reionization is the second of two major phase transitions of gas in the universe[citation needed] (the first is recombination). While the majority of baryonic matter in the universe is in the form of hydrogen and helium, reionization usually refers strictly to the reionization of hydrogen, the element.
It is believed that the primordial helium also experienced the same phase of reionization changes, but at different points in the history of the universe. This is usually referred to as helium reionization.
https://en.wikipedia.org/wiki/Reionization
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