The Earth’s tectonic plates started moving more than 3.2 billion years ago – just over 1.3 billion years after the Earth first formed and earlier than originally thought, researchers have revealed.
To date, some researchers theorised it happened around four billion years ago, while others thought it was closer to one billion.
According to the study, published in the journal Science Advances, the researchers from Harvard University looked for clues in ancient rocks (older than 3 billion years) from Australia and South Africa and found that these plates were moving at least 3.2 billion years ago on the early Earth.
In a portion of the Pilbra Craton in Western Australia, one of the oldest pieces of the Earth’s crust, scientists found a latitudinal drift of about 2.5 centimetres a year and dated the motion to 3.2 billion years ago.
The researchers believe this shift is the earliest proof that modern-like plate motion happened between two to four billion years ago. It adds to growing research that tectonic movement occurred on the early Earth.
“Based on the evidence we found, it looks like plate tectonics is a much more likely process to have occurred on the early Earth and that argues for an Earth that looks a lot more similar to today’s than a lot of people think,” said study researcher Alec Brenner from Harvard University in the US.
For the study, members of the project travelled to Pilbara Craton in Western Australia. A craton is a primordial, thick, and very stable piece of crust. They are usually found in the middle of tectonic plates and are the ancient hearts of the Earth’s continents.
This makes them the natural place to go to study the early Earth. The Pilbara Craton stretches about 300 miles across, covering approximately the same area as the state of Pennsylvania. Rocks there formed as early as 3.5 billion years ago.
In 2017, the researchers took samples from a portion called the Honeyeater Basalt. They drilled into the rocks there and collected core samples about an inch wide.
They brought the samples back to the lab in Cambridge, where they placed the samples into magnetometers and demagnetizing equipment. These instruments told them the rock’s magnetic history. The oldest, most stable bit of that history is hopefully when the rock formed. In this case, it was 3.2 billion years ago.
The team then used their data and data from other researchers, who’ve demagnetized rocks in nearby areas, to date when the rocks shifted from one point to another. They found a drift of 2.5 centimetres a year.
Researchers used the novel Quantum Diamond Microscope to confirm their findings from 3.2 billion years ago. The microscope images the magnetic fields and particles of a sample. It was developed in collaboration between researchers at Harvard and MIT.
In the study, the researchers point out they weren’t able to rule out a phenomenon called “true polar wander.” It can also cause the Earth’s surface to shift.
Their results lean more towards plate tectonic motion because of the time interval of this geological movement.
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