New research analyzing pieces of the most ancient rocks on the planet adds some of the sharpest evidence yet that Earth’s crust was pushing and pulling in a manner similar to modern plate tectonics at least 3.25 billion years ago. The study also provides the earliest proof of when the planet’s magnetic north and south poles swapped places. The two results offer clues into how such geological changes may have resulted in an environment more conducive to the development of life on the planet.

The work, described in PNAS and led by Harvard geologists Alec Brenner and Roger Fu, focused on a portion of the Pilbara Craton in Western Australia, one of the oldest and most stable pieces of the Earth’s crust. Using novel techniques and equipment, the researchers show that some of the Earth’s earliest surface was moving at a rate of 6.1 centimeters per year and 0.55 degrees every million years.

That speed more than doubles the rate the ancient crust was shown to be moving in a previous study by the same researchers. Both the speed and direction of this latitudinal drift leaves plate tectonics as the most logical and strongest explanation for it.

“There’s a lot of work that seems to suggest that early in Earth’s history plate tectonics wasn’t actually the dominant way in which the planet’s internal heat gets released, as it is today, through the shifting of plates,” said Brenner, a Ph.D. candidate in the Graduate School of Arts and Sciences and a member of Harvard’s Paleomagnetics Lab. “This evidence lets us much more confidently rule out explanations that don’t involve plate tectonics.”

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