Magnetic clues in Australian rocks suggest plate tectonics began more than 3 billion years ago

Without plate tectonics, our planet would have no continents, mountains and possibly even life itself. New evidence suggests that this geological process began at least 3.2 billion years ago, surprisingly early origin.

Sunthe eologists debate exactly when the tectonic plates of our planet began to change. Estimates vary greatly, from 4 4 billion to 1 A billion years ago, with the general agreement that it started about 2.8 billion years ago.

New investigation published today in Science Advances suggests that deep plates below the surface were moving 3.2 billion years ago. Ancient Australian rocks were found to have magnetic signatures that could be correlated with lateral movements during the Arcean eon (4 billion to 2.5 billion years).

“Basically, this is a piece of geological evidence to extend the record of plate tectonics on Earth further back in Earth’s history,” said Alec Brenner, co-author of the study and a geologist at the Paleomagnetic Laboratory at Harvard University. , in a press release. . “Based on the evidence we find, it appears that plate tectonics is a much more likely process to have occurred on early Earth and that it advocates an Earth that looks much more like today’s than most people think.”

Plate tectonics is a critical feature of our planet, giving origin and shape to our continents and forging land formations like mountain ranges. Importantly, plate tectonics shook rocks far below the surface, pushing them up and exposing them to the atmosphere. This in turn led to key chemical reactions that, on painfully long timescales, contributed to the stabilization of Earth’s atmosphere, which ultimately created livable conditions that we know and whatgo.

For the new study, Brenner and colleagues visited Western Australia, where they sampled rocks from the Pilbara Craton, an ancient and stable bark extension that measures more than 420 kilometers (260). miles long. Some rocks in Pilbara Craton are 3.5 billion years old, representing some of the oldest crusts on Earth.

The team took 235 main samples in 2017 from a segment known as Honeyeater Basalt. The remarkable thing about these volcanic rocks is that they are magnetically oriented, which means they have kept a record of Earth’s magnetic field as it existed when rocks cooled and solidified during the Arcean

In In the laboratory, these magnetic signatures, along with the known ages of basalt, were used to infer the movement of rocks over millions of years. The researchers were able to demonstrate that the rocks were moving between 3.35 billion and 3.18 billion years ago. and that they changed in a horizontal direction at a rate of about 2.5 centimeters (0.98 inches) each year, a “speed comparable to that of modern plates,” as the authors wrote in their article.

Previous techniques to detect the onset of plate tectonics used methods such as measuring the positions of rocks over time and identifying chemical signatures on rocks consistent with movement. The new document applies a paleomagnetic approach, setting an early date for plate tectonics on Earth, around 1.3 billion years after the formation of our planet. Furthermore, the new document reinforces the claim that the alterations of the early earth’s crust were due to these slow and constant movements.

Stephan Sobolev, a professor of geodynamics at the University of Potsdam, said the new measurements “seem convincing.” He told Gizmodo that he “s grateful for the new data on Archean Earth, particularly data pertaining to the early paleomagnetic history of our planet, saying: “In this sense, it is a great job.” But he doesn’t think the researchers have confirmed the presence of modern plate tectonics as we observe it today.

“This is the first indication of a large scale … displacement of the earth’s crust more than 3.2 billion years ago “ Sobolev, who was not involved in the new investigation, wrote in an email to Gizmodo. “Such displacement is an indication of a type of plate tectonics (but not necessarily the modern global type of plate tectonics) and a large-scale subduction,” when the plates move sideways and downward..

It is possible, Sobolev said, that the authors detected a special “regional type” of plate tectonics, which may have existed in different places on Earth at the time. and was potentially caused by mantle feathers or meteoric impacts, according to a recent Nature paper Sobolev co-author

“But any type of plate tectonics requires great-scale subduction so for me this work provides new evidence of greatscale subduction on Earth already more than 3.1 billion years ago, “Sobolev said, adding that “it would be great if similar data were collected” on other cratons dating from the same time period.

Another important caveat is a phenomenon known as the True Polar Wander, something the researchers couldn’t rule out as the cause of the observed displacement. True Polar Wander describes the reorientation of a planet with respect to its axis of rotation. This can happen due to plate tectonics, but other factors can cause the Earth’s surface to shift, such as supervolcanic activity, the melting of massive ice sheets, or anything else that can alter the distribution of the planet’s mass. . and therefore the way it rotates along its axis.

“Typical True Polar Wander estimates for the last hundred million years on Earth generate movements faster than its 2.5 centimeters per year, but we don’t know how this worked during Archean,” Sobolev said.

Consequently, the authors said that True Polar Wander could explain their data, but plate tectonics is a better option given the observed time intervals.

Looking to the future, researchers would like to study more samples of Pilbara Craton and other ancient rock deposits.