Naked Science Forum
Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: Don_1 on 30/11/2012 13:37:58
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If we accept that about 4 - 5b years ago a belt of asteroids etc from tiny grains to huge million ton chunks of rock and metals orbiting the Sun began to collide and formed planet Earth, then we must accept that among this would have been huge cosmic ice bergs.
The multitude of impacts resulted in a planet of molten rock with the ice bergs being turned into water vapour. Over the next few hundred million years Earth's atmosphere would have been a hostile mix of methane, ammonia, hydrogen sulphide and other noxious gases and trillions of gallons of super heated steam.
The clouds would have been so dense over the entire planet, and stretching from ground level to the upper atmosphere, as to block out the Sun completely. On the side of the planet facing the Sun, the water vapour in the upper atmosphere would have been kept hot by the Sun's rays, while that at ground level would have been kept hot by the Earth's molten surface. But on the other side of the planet, the dark side, the vapour in the upper atmosphere would have cooled and condensed, to fall as rain. As the Earth rotated, this would have happened over the entire planet in a uniform manner. As cold water, falling as rain, passed through the hot steam at lower levels, it would have had a cooling effect on the vapour at lower altitudes and over the next few hundred millions of years, it may have contributed to the cooling of the Earth's surface and the eventual formation of the crust.
Now, given that the ‘solid’ Earth and the gaseous Earth would have both been fairly uniform, it would be reasonable to assume that when water vapour turned to precipitation and finally remained liquid on the Earth's surface, it would have done so in a uniform manner. The result of this would have been that Earth's crust would have been entirely submerged.
The crust would still have been extremely hot and perhaps just a few metres thick. Earth would have been like a cook's steamer, with constant evaporation, condensation and precipitation. At crust level, the vast single ocean would have been boiling violently, while at surface level the ocean may have been just a degree below boiling point. With Earth remaining highly volatile, continual eruptions would have seen the occasional volcanic island emerging from the ocean, only to be flattened by the corrosive water and the action of extreme tidal activity caused by other eruptions elsewhere.
A few hundred million years on, with continued cooling and thickening of the crust, the situation would have begun to stabilise. With fewer eruptions and the ocean temperature reduced to say 50oC, some of the volcanic islands may have been able to survive for many hundreds or thousands of years. These islands may even have survived another local eruption and become joined to form double and triple volcano isles. High numbers of massive eruptions concentrated in one area could explain the formation of the first land masses of Vaalbara and even Ur. But how did the subsequent supercontinents form?
Could it be that the tectonic plates which surrounded the plates upon which Pangaea sat, all began to converge over a period of a couple of billion years, gradually lifting just one huge land mass out of the ocean? Starting with Rodinia, Pannotia, Oldredia and finally Eramerica until the whole Pangaea land mass was raised above sea level.
Why a supercontinent? Why not smaller continents more evenly spread? And perhaps the crux of the whole matter, how and why did the tectonic plates evolve?
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… Earth's atmosphere would have been a hostile mix of methane, ammonia, hydrogen sulphide and other noxious gases …
One life-form’s meat is another’s poison (http://idioms.thefreedictionary.com/One+man%27s+meat+is+another+man%27s+poison) …
Free oxygen is toxic to anaerobic organisms and the rising concentrations may have wiped out most of the Earth's anaerobic inhabitants at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earth's history.
http://en.wikipedia.org/wiki/Oxygen_Crisis
Q. How did dry land form?
or to put that another way ... "Why isn't the Earth completely covered in water?" ... http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008LPI....39.1158N&link_type=ARTICLE&db_key=AST&high=
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First of all, you are making one very incorrect assumption. You state that, "But on the other side of the planet, the dark side, the vapour in the upper atmosphere would have cooled and condensed, to fall as rain." By stating that, you are assuming that every time it becomes night in an area on Earth, it should rain. This is oviously not the case. The heat radiating from the Earth had a much larger affect on the state of the volatiles than whether it was light or dark.
Also, the Earth's crust crystallized before the condensation of any liquid water on the Earth's surface. It is quite a reach to assume that the crust formed perfectly uniform relief all around the Earth; thus, ocean basins would form in the lower areas.
Assuming that any volcanic islands would immediately be weathered away to nothing sounds incorret as well. However, I will agree with you that weathering was much more agressive in the Hadean/Archean due to a more active hydrological cycle and an acidic atmosphere.