There is a difference between warm lithospheric plate tectonics and cold ice plate tectonics. I think the Earth is the only planet with plates that are made of rock. However, the article below has links to sites that suspect Mars and Venus both may have plate tectonics of a sort.
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Originally Posted by [url=http://en.wikipedia.org/wiki/Plate_tectonics
Wikipedia Article on Plate Tectonics[/url]]Tectonic plates are comprised of two types of lithosphere: continental and oceanic lithospheres; for example, the African Plate includes the continent and parts of the floor of the Atlantic and Indian Oceans. The distinction is based on the density of constituent materials; oceanic lithospheres are denser than continental ones due to their greater mafic mineral content. As a result, the oceanic lithospheres generally lie below sea level (for example the entire Pacific Plate, which carries no continent), while the continental ones project above sea level (see isostasy for explanation of this principle, which is essentially a large-scale version of Archimedes' Bath).
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Furthermore, some suspect that the reason we have continents is because of the moon-creating impact.
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Originally Posted by [url=http://en.wikipedia.org/wiki/Giant_impact_theory
Wikipedia article on Giant Impact Theory[/url]]Other than the existence of the Moon itself, the primary legacy of this event, say researchers, is the fact that the Earth does not have enough of the lighter-colored felsic and intermediate rock-types to completely cover its entire surface. Thus we have continents made from felsic rocks and ocean basins which are made of the darker-colored, heavier and more metal-rich mafic rock types. This difference in composition along with the presence of water allows for an extensively active system of plate tectonics on the Earth. Others have postulated that the axial-tilt and initial rotation of the Earth had their origin with the so-called giant impact.
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If the Venusian and Marsian plate systems don't recycle carbon and water like the earth's system seems to and if they have nearly 100% coverage then we might conclude that too much felsic material eventually siezes and stops the cycles. This might indicate that a long lived life-bearing world should have a giant impact to remove the felsic material. However, the above article also suggests that the rareness of such an event may be mitigated by a hypothesis of impactor formation co-orbital with earth at L4. Depending on the theories, it could support the low probability of life in the universe, or increase the chances.
06-July-2005, 10:22 PM
Are Planets With Live Plate Tectonics...
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