By Scientists studying rocks in South Africa report evidence for the earliest known earthquake triggered by plate tectonics. The temblor struck more than 3 billion years ago.
The rocks preserve telltale signs of ancient submarine landslides that tend to occur in response to giant earthquakes set off by some collisions of slabs of the planet’s crust, geologists Cornel de Ronde and Simon Lamb report February 27 in Geology.
Finding evidence of such a giant earthquake so early in Earth’s roughly 4.5-billion-year history throws a spotlight on a hotly debated topic in geology: When did plate tectonics, the constant movements of interlocking pieces of crust, arise (SN: 1/13/21)?
Some geologists think it took a while for plate tectonics to emerge, no earlier than 2.8 billion years ago. Others argue it began much earlier (SN: 4/22/20). It’s hard to know for sure because very few rocks from this period of the planet’s history exist anymore.
“I am a strong advocate … of the other argument that plate tectonics has been with us at least as long as the oldest rocks preserved on Earth, and probably even much before,” says Timothy Kusky of the State Key Lab for Geological Processes and Mineral Resources in Wuhan, China. “This study lends strong support to this second view.”
De Ronde, of GNS Science in Lower Hutt, New Zealand, had mapped the distribution of the belt’s different rock types and published the results in 2021. When Lamb, of the Victoria University of Wellington, saw the map, he spotted something surprising: The distribution of ancient rock layers and formations looked a lot like Lamb’s map of the distribution of submarine landslides in New Zealand that were triggered by earthquakes relatively recently in geologic time.
“It’s different rock, but the way the rocks were arranged was uncannily similar,” Lamb says. “It unlocked the whole mystery of these early rocks.”
The comparison suggests the Barberton rocks, like those in New Zealand, held signs of being churned by giant submarine landslides, and those landslides tend to occur in the wake of earthquakes caused by two tectonic plates colliding and one thrusting atop the other. This process, called subduction, can be so forceful that it causes megathrust earthquakes, such as the magnitude 9.1 earthquake in Indonesia in 2004 and the magnitude 9.0 temblor in Japan in 2011 (SN: 5/2/2022).
The study offers “some of the earliest evidence for giant subduction megathrust earthquakes,” Kusky says. It’s the fieldwork that makes the argument convincing, he notes. With fieldwork, assumptions about earthquakes and plate tectonics aren’t based on idealized models, but the rock record, which contains solid, verifiable evidence.
But Richard Palin, a geologist at the University of Oxford, isn’t entirely convinced. The initiation of plate tectonics, which today operates across the entire planet, is not a clean-cut story, he says (SN: 4/9/22).
“Some scientists may believe that subduction initiated everywhere all at once, hence the onset of plate tectonics is a bit like flipping a switch,” he says. “This seems very unlikely to me.” Palin suspects that subduction began in different places on Earth at different times.
