How the Earth’s tectonic plates began to move

The Earth’s tectonic plates began to move thanks to the eruption of continents that pushed them apart, scientists at the University of Sydney believe.

The process has been a mystery until now.

“The geological record suggests that until three billion years ago the earth’s crust was immobile so what sparked this unique phenomenon has fascinated geoscientists for decades,” says lead author of the study Professor Patrice Rey, from the University of Sydney’s School of Geosciences.

“We suggest it was triggered by the spreading of early continents then eventually became a self-sustaining process.”

There are eight major tectonic plates that move above the earth’s mantle at rates up to 150 millimetres every year.

The process involves plates being dragged into the mantle at certain points and moving away from each other at others, in what has been dubbed “the conveyor belt”.

Earth is the only planet in our solar system where the process of plate tectonics occurs and the dynamic was only relatively recently discovered, as Cosmos explained in a recent article.

Plate tectonics depends on the inverse relationship between density of rocks and temperature.

At mid-oceanic ridges, rocks are hot and their density is low, making them buoyant or more able to float. As they move away from those ridges they cool down and their density increases until, where they become denser than the underlying hot mantle, they sink and are ‘dragged’ under.

But three to four billion years ago, the earth’s interior was hotter, volcanic activity was more prominent and tectonic plates did not become cold and dense enough to spontaneously sank.

“So the driving engine for plate tectonics didn’t exist,” said Professor Rey said.

“Instead, thick and buoyant early continents erupted in the middle of immobile plates. Our modelling shows that these early continents could have placed major stress on the surrounding plates. Because they were buoyant they spread horizontally, forcing adjacent plates to be pushed under at their edges.”

The study was published in Nature today.

The other authors on the paper are Nicolas Flament, also from Sydney’s School of Geosciences and Nicolas Coltice, from the University of Lyon.

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