Earth’s Tectonic Activity May Be Crucial for Life — and Rare in Our Galaxy
Our planet is in constant flux. Tectonic plates—the large slabs of rock that divide Earth’s crust so that it looks like a cracked eggshell—jostle about in fits and starts that continuously reshape our planet—and possibly foster life.
These plates ram into one another, building mountains. They slide apart, giving birth to new oceans that can grow for hundreds of millions of years. They skim past one another, triggering earth-shattering quakes. And they slip under one another in a process called subduction, sliding deep into the planet’s innards and producing volcanoes that spew gases into the atmosphere.
And not only is Earth alive, it is a vessel for life. Because it is the only known planet to host both plate tectonics—that ongoing shuffling of tectonic plates—and life, many scientists think the two might be related. In fact, some researchers argue that shifting plates, which have the ability to help regulate a planet’s temperature over billions of years, are a crucial ingredient for life.
This connection raises the tantalizing possibility that if scientists could find exoplanets that quake and rumble, they might be able to find life beyond our Pale Blue Dot. So, Cayman Unterborn, an astronomer at Arizona State University, set out to determine the likelihood that distant exoplanets undergo plate tectonics. In a paper posted July 3 to the preprint server arXiv and currently undergoing peer review, he and his colleagues found that the majority of exoplanets are probably unable to sustain plate tectonics over long periods of time.
Their results are still uncertain because scientists do not fully understand how plate tectonics began on Earth (let alone on how they would other planets), but they do suggest that even if the process does begin, it may not last. That means Earth is not only the sole planet known to host moving plates in the solar system (although some recent evidence suggests Mercury might as well), it might also be one of a low number of such planets across the Milky Way.
“If you do need plate tectonics [for life], this paper sounds like bad news,” says John Armstrong, an astronomer at Weber State University who was not involved in the study. Still, astronomers suspect that as many as 40 billion potentially habitable Earth-size planets dot the galaxy. Even if only a third of these planets can sustain plate tectonics (as Unterborn’s study suggests), those roughly 13 billion planets, Armstrong says, are “still a lot of possible habitable worlds!”
But just how essential is plate tectonics for life? Hints can be found from our own planet’s history. Around 2.5 billion years ago the sun was so cold that Earth’s liquid oceans should have been frozen in a snowball-like state—only they were not.
Scientists think plate tectonics, which acts as a global thermostat, might have been our savior by creating volcanoes that spewed carbon dioxide into the atmosphere, helping it to retain more heat.
Then, as the sun grew brighter and hotter, rainfall scrubbed the carbon dioxide from the atmosphere and plate tectonics later subducted it into the Earth’s mantle (the layer of hot rock above the core), locking it away. It is this cycle, which acts on million-year timescales, that helps keep Earth’s temperature stable enough to support life.
Read rest at Scientific American
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