Scientists may have discovered the world’s oldest archery fault in the remote deserts of Northwest Australia. The discovery indicates that plate tectonic processes were active at least 3 billion years ago, fueling ongoing scientific debate.
“This study clearly shows horizontal plate movements before 3 billion years ago,” study co-author Timothy Kuskydirector of the Center for Global Tectonics at China University of Geosciences, told Live Science.
In the new study, published July 15 in the journal Geology, researchers found that about 3 billion years ago, large city-sized blocks of rock moved horizontally past each other for at least 19 miles (30 kilometers). The patterns resemble what geologists call arc shear transform faults, seen in active volcanic arcs such as the Andes and Sumatra. If the findings are correct, these impact rocks could be the earliest evidence of horizontal plate movements, the researchers said, although not all experts are convinced.
Plate tectonics, the theory that underpins Earth’s geological activity, shapes our planet with mountains, moving continents, and seismic upheavals. However, determining the origin of this fundamental process remains a controversial debate.
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mODELS show that the early Earth had less developed convection currents needed to drive plate tectonics, suggesting that a thick, rigid outer crust formed a “stagnant lid,” limiting dynamic horizontal motions. While bodies of magma may have risen and solidified, solid plates could not collide or subduct to form the volcanic mountain chains observed today. The debate centers around when convection currents developed, allowing Earth’s “stagnant lid” to break off into individual tectonic plates.
Some scientists argue that plate tectonics began in the Hadean, over 4 billion years ago. Others believe that the primitive “single cap” or “stagnant cap” dominated the early Earth until about 1 billion years ago.
The ultimate in AI modeling suggests that tectonic activity may date back to the Hadean Eon, over 4 billion years ago. However, validating models with direct data from Earth’s oldest and sparsely preserved rocks is a monumental challenge.
Studying these early processes is difficult due to the lack of ancient rocks. But Australia’s Pilbara Craton, with its 3.59-billion-year-old rocks, is a vital region for understanding the origins of plate tectonics. “The Pilbara Craton is where geologists first defined the ‘stagnant lid’ hypothesis,” Kusky said. The Mulgandinnah Shear Zone—a vast region of intense deformation, including horizontal faulting, within the Pilbara Craton—can provide crucial insights into this debate.
The researchers used classical field observations and high-resolution magnetic data to correlate the buried features with surface geology. They built on previous studies dating the movement to about 3 billion years ago, using structural geology techniques to reconstruct the displacement of large, once-connected rock bodies by at least 19 miles (30 kilometers).
When plates collide at odd angles in today’s volcanic arcs, arc shear transform mistakes develop by enabling horizontal and vertical movement. Because the rock types and destruction patterns of the Mulgandinnah Shear Zone are so similar to modern volcanic arcs, Kusky explained that only deep subduction, where one plate slides under another, could be responsible for these observations. Consequently, these findings corroborate recent AI models that suggest plate tectonics was active at least 3 billion years ago, and possibly over 4 billion years ago.
These studies “represent the final nails in the myth that a stagnant lid dominated the early Earth,” Kusky said.
Not everyone agrees that this new study settles the debate. Taras Gerya, a professor of Earth sciences at the Swiss Federal Institute of Technology in Zurich, who was not involved in the study, remains cautious. “There is no consensus on diving evidence in the Pilbara,” he told Live Science. He suggested that other processes could produce similar observations. “This fault pattern can also develop in a so-called rigid-cap regime,” he added, noting an intermediate state where the Earth’s lithosphere behaves as a “scratched” or semi-rigid layer rather than a fully rigid plate.
However, Simon Lamb, an associate professor of geology at Victoria University of Wellington Te Herenga Waka in New Zealand, who reviewed the study, finds the evidence compelling. “It’s hard to predict how such large displacements could have occurred without subduction. So I see this as compelling evidence for plate tectonics,” Lamb told Live Science.
Kusky sums it up: “If it looks like her, smells like her, it’s probably her.”