Plate tectonics account for everything from the growth of mountains to the rearrangement over time of oceans and continents, but they are also the reason our planet is habitable. When an oceanic plate bumps into a continental plate, it starts sliding beneath the continental one, carrying water and carbon dioxide in vast quantities into the interior of the planet. (Many scientists believe that there’s more water in the mantle than in all the oceans of the world combined.) These are then gradually released via volcanic eruptions, forming what Bjornerud calls “an ultraslow-motion, planetary-scale respiratory system,” without which we would have long since lost our atmosphere. Such was the fate of Mars, which has a single, rigid, planetwide plate that does not move relative to its mantle. Indeed, to the best of our knowledge, Earth is the only planet that has continents.
Kathryn Schulz em resenha de Marcia Bjornerud’s Turning to Stone
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