Her computer models have shown that plate tectonics, the forces that move continents and lift gigantic mountain ranges, are key to life on Earth as we know it, and possibly to life on other worlds. That's because as the rocky plates that form the planet's outer shell move about, they also recycle carbon dioxide. This greenhouse gas keeps our planet's temperature balmy, but not too hot. And the telltale signal would be certain levels of carbon dioxide, suggesting that just as on Earth, this other world relies on plate tectonics to cycle carbon.
But first things first. "There's no doubt that other Earths exist, simply due to the sheer vast numbers of other stars and galaxies in our universe," Marcy said. "There's a deeper question — how common are Earth-like planets? Are Earth-like planets a dime a dozen, or are they quite rare, quirky precious planets that are one in a thousand or one in a million?"