Friday, June 28, 2013

Where Did Water on Earth Come From? Venus, Earth and Mars

Water On Earth Brings You Here?

My Very Educated Mother Just Served Us Nine Pies. If 2nd grade wasn’t yesterday you might have forgotten this mnemonic device. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (Pluto omitted)— the order of the planets moving away from the sun.
To understand how water remained on Earth, Marcia Bjornerud pictures the three neighboring planets Venus, Earth, and Mars. The mass of planets is generally given in yoctograms (Yg). One yoctogram is equivalent to 10^21 kilograms when mass is given relative to mass on Earth. Mars is approximately 0.11 Yg, Earth 1 Yg, and Venus 0.88 Yg according to NASA’s calculations. An effect of Mars being so small in mass is that it does not have the gravitational pull to maintain an atmosphere. Venus, which is much more similar to Earth in mass, maintains close proximity to the sun. This proximity prevents Venus from being able to stabilize its temperature. At the beginning of formation all three of these planets were too close to the sun to have actually had water in the pure form, H2O. This is why scientists guess that water resided on the planet in the form of hydrous silicate minerals we call amphiboles.
An example of an amphibole is a form of asbestos, Ca2Mg5Si8O22(OH)2. General chemistry would tell you that under tremendous heat and pressure these atoms could rearrange themselves to produce 1 molecule of water for every 8 molecules of silicon. These amphiboles are predicted to rearrange molecularly at a depth of 60 miles beneath the surface of the Earth. This answers the question of where Earth’s “native” water came from.
However, the answer to where water came from does not stop at the dehydration of asbestos. Researchers conjecture that comets supplied Earth with up to 50 percent of its water. Wherever it came from, water is implicated in nearly EVERY geological process that takes place on Earth above and below our surface. 

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