Scientists finding out rocks in South Africa report proof for the earliest identified earthquake triggered by plate tectonics. The temblor struck greater than 3 billion years in the past.
The rocks protect telltale indicators of historical submarine landslides that are inclined to happen in response to large 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.
Discovering proof of such an enormous earthquake so early in Earth’s roughly 4.5-billion-year historical past throws a highlight on a hotly debated matter in geology: When did plate tectonics, the fixed actions of interlocking items of crust, come up (SN: 1/13/21)?
Some geologists assume it took some time for plate tectonics to emerge, no sooner than 2.8 billion years in the past. Others argue it started a lot earlier (SN: 4/22/20). It’s laborious to know for certain as a result of only a few rocks from this era of the planet’s historical past exist anymore.
“I’m a powerful advocate … of the opposite argument that plate tectonics has been with us a minimum of so long as the oldest rocks preserved on Earth, and doubtless even a lot earlier than,” says Timothy Kusky of the State Key Lab for Geological Processes and Mineral Assets in Wuhan, China. “This examine lends robust assist to this second view.”
De Ronde, of GNS Science in Decrease Hutt, New Zealand, had mapped the distribution of the belt’s completely different rock sorts and printed the leads to 2021. When Lamb, of the Victoria College of Wellington, noticed the map, he noticed one thing shocking: The distribution of historical rock layers and formations seemed lots like Lamb’s map of the distribution of submarine landslides in New Zealand that have been triggered by earthquakes comparatively lately in geologic time.
“It’s completely different rock, however the best way the rocks have been organized was uncannily comparable,” Lamb says. “It unlocked the entire thriller of those early rocks.”
The comparability suggests the Barberton rocks, like these in New Zealand, held indicators of being churned by large submarine landslides, and people landslides are inclined to happen within the wake of earthquakes attributable to two tectonic plates colliding and one thrusting atop the opposite. This course of, known as subduction, will be so forceful that it causes megathrust earthquakes, such because the magnitude 9.1 earthquake in Indonesia in 2004 and the magnitude 9.0 temblor in Japan in 2011 (SN: 5/2/2022).
The examine provides “among the earliest proof for big 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 primarily based on idealized fashions, however the rock file, which incorporates stable, verifiable proof.
However Richard Palin, a geologist on the College of Oxford, isn’t totally satisfied. The initiation of plate tectonics, which right now operates throughout the whole planet, shouldn’t be a clean-cut story, he says (SN: 4/9/22).
“Some scientists could imagine that subduction initiated in all places unexpectedly, therefore the onset of plate tectonics is a bit like flipping a change,” he says. “This appears not possible to me.” Palin suspects that subduction started somewhere else on Earth at completely different instances.
