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Nature

Plate Tectonics May Have Started Shifting Much Earlier In Earth's History Than Thought

author

Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockApr 22 2020, 19:00 UTC

An artistic cross-section through a forming crust approximately 3-4 billion years ago. (c) Alec Brenner, Harvard University.

Plate tectonics is a feature that, as far as we know, is unique to Earth. The outer surface of our planet is divided into 15 rigid blocks of crust that push up against each other. The movement of these blocks has shaped continents, oceans, and mountains. It is unclear when tectonics started on Earth but new research has found evidence that suggests they were moving at least 3.2 billion years ago, much earlier than thought.

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The study published in Science Advances looked for clues in the incredibly ancient rocks of Western Australia, specifically the Honeyeater Basalt, part of the East Pilbara Craton, one of the best-preserved pieces of Earth's crust, dating back over 3 billion years old. The team led by Harvard University researchers studied the rocks and found a latitudinal drift of 2.5 centimeters per year over a period of 170 million years. That is consistent with the speed that tectonic plates move on modern-day Earth.

Their work adds to the growing catalog of evidence suggesting a much earlier kick-off point for Earth’s plate tectonics, sometime between 2-4 million years ago. Previously, no evidence had been provided to push the date past 2.7 billion years ago, but this new research suggests that around 3.2 billion years ago this was already happening.

"Basically, this is one piece of geological evidence to extend the record of plate tectonics on Earth farther back in Earth history," Alec Brenner, one of the paper's lead authors from Harvard's Paleomagnetics Lab, said in a statement. "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."

The finding is intriguing but further evidence will likely need investigating before it can be confirmed. The motion indicating tectonic movement detected in the samples could be explained by other phenomena, such as a shift in the true poles of the planet. However, the team believes that evidence is in favor of early tectonics and they are now planning how best to test this. Collecting samples form equally ancient locations will help confirm or deny the origin of these motions.

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"We're trying to understand the geophysical principles that drive the Earth," added Roger Fu, another of the paper's lead authors. "Plate tectonics cycle elements that are necessary for life into the Earth and out of it."

It’s not just the cycle of elements that make plate tectonic important for life. The motion of the crust creates new landmasses, and those newly exposed rocks react with Earth's atmosphere. These chemical reactions have been key to the stabilization of Earth's climate and surface temperature (crucial to life) over billions of years.

Prof Roger Fu on an outcrop of the Honeyeater Basalt in Western Australia’s Pilbara Craton, one of the oldest pieces of Earth's crust. The ancient lavas exposed here showed that the Pilbara Craton moved over the Earth’s surface some 3.2 billion years ago. Credit: Alec Brenner, Harvard University.

 

A geologic map of the Pilbara Craton. The rocks exposed here range from 2.5 to 3.5 billion years ago, offering a uniquely well-preserved window into Earth’s deep past. Lavas samples (shown in green) used in the study dated to 3.2 billion years ago. Credit: Alec Brenner, Harvard University. Map data from the Geological Survey of Western Australia.

Nature