What this means for other planets in other solar systems is that plate tectonics can expand the Goldilocks zone of habitability around a star -- where it's neither too hot nor too cold -- by allowing a planet to better regulate its own temperature and keep water wet. Very large, rocky planets -- those super-earths -- would be the most likely places for life because their greater internal heat causes them to experience larger forces on thinner plates, Valencia asserts. As a result, they would be particularly good at regulating their climates and allowing life to evolve. It's likely that the lack of plate tectonics is the reason that both Mars or Venus -- Earth's closest local sibling planets -- are dead, Valencia explained. "If Mars were to have plate tectonics, it would have to be bigger early on," said Valencia. This is because plate tectonics require a planet to have a lot of interior heat to keep things moving. Smaller planets dissipate their heat faster, and so have a very short window of time for plate tectonics. Venus, on the other hand, is about the same size as Earth, but it lacks water, said Hansen. Without water in the mantle to help melt rocks and trigger volcanic recycling of material, Venus' crust appears to have remained stiff and locked up forever. Had Venus held more water, or if it had been a super-sized rocky planet, it too would have had plate tectonics and perhaps life. The implication of all this, of course, is that little old Earth lucked out. A little less water and the planet may not have had plate tectonics. Climate swings would have been harsher, and life might have foundered early on. Earth, just barely large enough to have the internal heat; just wet enough to melt and recycle its crust -- may have barely made the cut for life. Related Links: |
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