About 3.2 billion years ago, when Earth was still a far more inhospitable place than it is today, a geological process would have begun that would completely (and constantly) change its face: the movement of tectonic plates.
At about the same time, about halfway through the Archean eon (between 4 billion and 2.5 billion years ago), our planet was bombarded by violent impacts.
In an article published last Friday (22) in the journal Geology, researchers suggest that colossal collisions of extraterrestrial bodies would have triggered the terrestrial transition from its warm, primitive state to the world we know: with the fragmented lithosphere (crust and upper mantle).
“We often think of Earth as an isolated system where only internal processes matter,” co-author Craig O’Neill said in a statement.
“Increasingly, however, we are seeing the effect of the dynamics of the solar system on how the earth behaves,” adds the director of the Planetary Research Center at Macquarie University in Australia.
Studying certain sedimentary layers located in Australian and South African soils, O’Neill and colleagues found that in those fateful times, 3.2 billion years ago, the Earth was particularly hard hit with many impacts.
So they created a series of simulations and models to first understand the extent and frequency of these impacts – and then whether they would have been able to initiate global tectonics.
Because, unlike the first hundreds of millions of years of Earth’s life (formed 4.6 billion years ago), where collisions of bodies of 300 kilometers in diameter were frequent, in the Archean they decreased slightly.
Evidence indicates that most impacts at this time were no more than 100 kilometers in diameter (30 kilometers larger than the asteroid that killed the dinosaurs).
To check whether even these minor events were enough to fragment the lithosphere, scientists used techniques to estimate the amount of impacts on the Mesoarchean and created simulations to model the effects of these collisions on mantle temperature.
The results indicate yes: these kilometer celestial bodies that bumped into our planet may well have created the tectonic plates.
Since neither the lithosphere nor the mantle were very homogeneous there, with some parts thinner and others thicker, the impacts further accentuated these buoyancy differences in the mantle – and thus tectonic plates would have emerged.