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Earliest Zircons formed under "Venus-like" Atmosph
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Widdekind
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| Verfasst am: 27.01.2009 12:19 Titel: Earliest Zircons formed under "Venus-like" Atmosph |
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Earth's early atmosphere was much like Venus'. It was dense, heavy, & high-pressure, composed primarily of Carbon-Dioxide. However, by being farther from the Sun, the Earth was comparatively cooler, so steam could condense as water, which then absorbed copious quantities of Carbon-Dioxide:
Zitat:
On Earth, the oceans dissolved a great deal of Carbon-Dioxide (they still do) and turned it into Carbonic Acid, which reacted with rocks and formed Carbonates. Today, the total amount of Carbon-Dioxide gas surrounding Venus is about 70 times the amount of air on Earth. But, if the Carbon-Dioxide tied up in Earth's Carbonate rocks was released into the atmosphere, the amount of Carbon-Dioxide in Earth's atmosphere would be about the same as the amount in Venus'*.
Today, Venus' dense atmosphere produces Pressures of 90 bars. And, the Solar Wind has steadily stripped off Venus' atmosphere "throughout the planet’s four-thousand million-year history"**. Thus, Venus' primordial atmosphere perhaps produced Pressures above 100 bars. Therefore, Earth's primordial atmosphere probably produced Pressures above 100 bars as well.
* Fred Schaaf. Planetology, pg. 89.
** http://www.esa.int/esaMI/Venus_Express/SEM0G373R8F_0.html ; http://www.hq.nasa.gov/osf/2007/2007_europe.htm
Now, when water is subjected to Pressures above 200 bars, and Temperatures above 646 K, "there is no physical distinction between a gas and a liquid"*. This is called water's Critical Point. Therefore, Earth's primordial atmosphere plausibly produced Pressures and Temperatures above water's Critical Point.
* Caleb A. Scharf. Extrasolar Planets & Astrobiology, pg. 367.
Moreover, some of Earth's earliest Zircons, from 4.0 - 4.2 billion years ago, "grew from water-saturated magmas"*.
* http://www.universityofcalifornia.edu/news/article/19054
CONCLUSION (??): Earth's primordial atmosphere created conditions of extreme Temperatures and Pressures, above water's Critical Point. Thus, early Zircons could have formed from "steam-saturated magmas", since such steam was equivalent to liquid water.
Therefore, early Zircons could have been created at Temperatures above 373 K, despite being born amidst liquid water. |
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Widdekind
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Early Earth may have had huge quantities of water, covering the globe to a depth of ~40 km*.
Thus, the early Earth may have originally had much more Atmosphere & Ocean. |
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