Ancient Rocks Reveal When Earth's Plate Tectonics Began

In 2016, the geochemists Jonas Tusch and Carsten Münker hammered a thousand pounds of rock from the Australian Outback and airfreighted it home to Cologne, Germany.

Five years of sawing, crushing, dissolving, and analyzing later, they have coaxed from those rocks a secret hidden for eons: the era when plate tectonics began.

Earth’s fractured carapace of rigid, interlocking plates is unique in the solar system. Scientists increasingly connect it to our planet’s other special features, such as its stable atmosphere, protective magnetic field and menagerie of complex life. But geologists have long debated exactly when Earth’s crust broke into plates, with competing hypotheses spanning from the first billion years of the planet’s 4.5-billion-year history to sometime in the last billion. Those estimates have wildly different implications for how plate tectonics affects everything else on Earth.

The spreading, smashing, and plunging of tectonic plates shapes far more than just geography. The recycling of Earth’s surface helps to regulate its climate, while the building of continents and mountains pumps vital nutrients into the ecosystem. Indeed, plate tectonics, if it began early enough, may have been a major driver of the evolution of complex life. And by extension, shifting plates could be a prerequisite for advanced life on distant planets as well.

Now, a study of the rocks from the Australian Outback by Tusch, Münker and their co-authors, published in Proceedings of the National Academy of Sciences, has captured “a snapshot” of the advent of plate tectonics, said Alan Collins, a geologist at the University of Adelaide in Australia. The team’s analysis of tungsten isotopes in the rocks reveals Earth in the act of transitioning to plate tectonics around 3.2 billion years ago.

Jonas Tusch, left, and Carsten Münker sledgehammering rocks from the Archean eon in Pilbara, Australia.Courtesy of Chris S. Marien
The findings buttress other circumstantial evidence accrued over the last decade pointing to that date, said Richard Palin, a petrologist at the University of Oxford. It “supports the growing consensus in the geological community that plate tectonics established itself at a global scale” sometime around 3 billion years ago, he said.“There’s a lot of different people, coming from very different perspectives, coming up with a convergence of 3.2 to 3 billion years,” said Collins.Earth’s EngineWhen the geologist Alfred Wegener first proposed the theory of continental drift in 1912, most of his colleagues thought it was preposterous. How could giant landmasses move? Wegener couldn’t identify a mechanism to drive his drifting continents. And indeed it would take another five decades for geologists to figure out how convection within Earth’s mantle—the thick layer of hot rock between the crust and core—propels the plates on the surface. They eventually showed that these plates—15 main ones and dozens of smaller ones—spread apart at mid-ocean ridges, move with the mantle’s flow, scrape against each other at their edges, and plunge back into the mantle at “subduction zones.”
“Plate tectonics gives a very organized way of moving the surface,” said Carolina Lithgow-Bertelloni, a geophysicist at the University of California, Los Angeles. “You can then understand why there are earthquakes where there are earthquakes, why there are mountains where there are mountains.”