The large-scale movement of massive slabs of rock that divide the Earth described by the theory of plate tectonics may be essential for life on this planet – and on other planets as well, according to new research posted online earlier this month on the arXiv prepublication repository.
Plate tectonics, Live Science explained, is the theory that the planet’s outer shell is divided into a number of plates that glide over the mantle (the rocky layer that surrounds the core). The concept builds on the theory of continental drift by explaining how landmasses move around the Earth.
The plates in question are part of the hard, rigid, outermost shell known as the lithosphere, which glide over the mantle. Their motion serves as the driving force behind all geological features on a planet’s surface, and that movement is the result of convection in the mantle, the website said.
According to Scientific American, Earth is the only planet known to host both plate tectonics and biological life, and many scientists believe that there could be a link between the two. Some even argue that by helping to regulate a planet’s temperature over billions of years, shifting plates may actually be an essential ingredient for the existence of living organisms.
To further investigate this potential link, Arizona State University researcher Cayman Unterborn and his colleagues set out to determine the chances that exoplanets could undergo plate tectonics. They concluded that most of these distant worlds would be unable to do so for prolonged periods of time, although the results remains somewhat inconclusive.
Elemental composition the key to sustainable plate tectonics
As Unterborn’s team explained in their paper, the tectonic processes that take place on Earth are driving largely by the sinking of cold subducting plates into the underlying mantle – which is due in part to metamorphic transitions in the basaltic oceanic crust and the lithospheric mantle.
Those transitions, the study authors explained, are dependant upon the elemental composition of our planet – specifically, the quantities of the planet-building elements magnesium, silicon, iron, calcium, aluminum and sodium, which they noted: “vary in abundance across the galaxy.” Planets with contain higher concentrations of silicon and sodium, the researchers found, are less likely to undergo sustained plate tectonics.
“We find only 1/3 of the range of stellar compositions observed in the galaxy is likely to host planets able to sustain density-driven tectonics compared to the… Earth,” Unterbone and his colleagues wrote. “Systems outside of this compositional range are less likely to produce planets able to tectonically regulate their climate and may be inhospitable to life as we know it.”
“If you do need plate tectonics [to maintain life], this paper sounds like bad news,” Weber State University astronomer John Armstrong, who was not involved in the study, said in an interview with Scientific American. However, given that experts believe that there may be up to 40 billion potentially-habitable Earth-sized planets in the galaxy, even if only one-third (around 13 billion) can sustain plate tectonics, that’s “still a lot of possible habitable worlds,” he added.
Image credit: ESA / Hubble, M. Kornmesser