The Earth is the only planet known to have continents adrift. Scientists are rather certain that the drifting began about a billion years into Earth’s history. This means that for a thousand million years, the continents just sat there. Idle.
Without the stress of plate tectonics, many believe that speciation – evolutionary change – would never have occurred. We owe our existence to the fact that the continents move. I wonder what that first moving day was like. Was it a sudden lurch, a jarring like a big transport truck in gear with the clutch popped out? What made the plate tectonics conveyor begin to convey?
Scientists at the Australian University of Sydney think they know. In Nature, Patrice Rey and Nicolas Flament (along with Nicolas Coltice of the Institut Universitaire de France) announced results of a mathematical study on the presumed early Earth crust. Their numerical modeling concluded that slow gravitational collapse of the early continents started episodic movements. But that couldn’t happen until after the surface cooled significantly. And with tidal heat from the closely orbiting moon and from the recently accumulated heat from bolide (asteroid and comet) bombardment, our planet was not cooling down very quickly. It took a billion years of idleness before conditions were right to allow subduction and plate movement.
In their paper, the authors write:
The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth’s interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining.
It took time. At first, the Earth’s surface was like hell – melted rocks, poisonous gases, fiery volcanoes. But now the system is set in motion with the spreading mid-ocean ridges and descending subduction zones, all powered by unfathomable heat. And it will continue until hell freezes over.