Plate Tectonics May Have Started Earlier Than Geologists Thought
By tracing the orientation of magnetic inclusions in The earth's oldest rocks, scientists found that the movement of lithospheric plates started more than 3.2 billion years ago.
The surface and even the atmosphere of our planet are formed under the huge influence of plate tectonics. But these slow movements of the earth's crust did not begin immediately. It is assumed that they could have been launched by a Late heavy bombardment or even a single impact of a massive asteroid that fell on a fairly thin section of the lithosphere. The time of this event remains unknown.
Estimates range from one to four billion years ago, although most often the beginning of plate tectonics is attributed to about 2.8 billion years ago. New work by Harvard geologists dates the launch of tectonics to a much older period of 3.2 billion years. This is reported in an article by Alec Brenner and his co-authors published in the journal Science Advances.
The authors studied the Pilbara craton — the oldest Foundation of the continental crust that comes to the surface in Western Australia. It is here that the oldest minerals on the planet are found, which are up to 3.5 billion years old. Back in 2017, the Brenner team collected 235 samples of ancient basalt in the craton.
Such rocks contain ferromagnetic inclusions that, like the arrows of tiny compasses, Orient themselves along the earth's magnetic field lines while It remains molten. As it cools and hardens, the stone registers the directions of the "arrows," which makes it possible to find out their original position even after billions of years. This work was carried out by scientists, who carefully dated each sample and tracked the changes in their orientation over hundreds of millions of years.
It was found that already between 3.5 billion and 3.2 billion years ago, the craton shifted horizontally at a speed of about 2.5 centimeters per year, about the same as the modern continents. In principle, other explanations of this process are possible: for example, local (regional) movements of the crust or the wandering of the Earth's true magnetic pole. However, the authors believe the most obvious explanation is most likely, concluding that plate tectonics could have started just 1.3 billion years after the formation of the planet itself.