Scientists have potentially uncovered the world’s oldest arc-slicing fault, located in the remote deserts of Northwestern Australia. This discovery provides compelling evidence that plate tectonic processes were active at least 3 billion years ago, reigniting a longstanding scientific debate.
The research, published in the journal *Geology*, revealed that around 3 billion years ago, massive rock blocks, the size of cities, moved horizontally past each other by at least 19 miles (30 kilometers). This pattern resembles what geologists call arc-slicing transform faults, commonly observed in active volcanic arcs like the Andes and Sumatra.
If these findings are accurate, these ancient rocks could represent the earliest evidence of horizontal plate movements. However, not all experts are convinced.
Plate tectonics, the fundamental theory behind Earth’s geological activity, is responsible for shaping our planet’s mountains, continents, and seismic events. Yet, pinpointing the origins of this crucial process remains a point of contention among scientists.
Models suggest that early Earth had less developed convection currents, necessary to drive plate tectonics. This suggests that a thick, rigid outer crust, known as a ‘stagnant lid’, limited dynamic horizontal movements.
The debate centers around the timing of the development of convection currents, which allowed Earth’s ‘stagnant lid’ to break into individual tectonic plates. Some scientists believe plate tectonics started in the Hadean eon, over 4 billion years ago. Others argue that a primitive ‘single lid’ or ‘stagnant lid’ dominated early Earth until about 1 billion years ago.
Recent AI modeling suggests tectonic activity may date back to the Hadean eon. However, validating these models with direct evidence from Earth’s oldest and rarely preserved rocks poses a significant challenge.
Australia’s Pilbara Craton, with its 3.59 billion-year-old rocks, is a crucial region for understanding the origins of plate tectonics. This is where geologists first defined the ‘stagnant lid’ hypothesis.
The Mulgandinnah shear zone, a vast region of intense deformation within the Pilbara Craton, including horizontal faulting, could provide crucial insights into this debate.
Researchers utilized classic field observations and high-resolution magnetic data to connect buried features with surface geology. They built upon previous studies that dated the movement to around 3 billion years ago, employing structural geology techniques to reconstruct the displacement of large rock bodies.
When plates collide at unusual angles in today’s volcanic arcs, arc-slicing transform faults develop, facilitating both horizontal and vertical movement. Due to the striking similarities between the Mulgandinnah shear zone’s rock types and destruction patterns and those of modern volcanic arcs, researchers believe that only deep subduction, where one plate slides beneath another, can account for these observations.
These findings validate recent AI models suggesting that plate tectonics were active at least 3 billion years ago, and potentially even over 4 billion years ago.
While the study provides compelling evidence, not all scientists agree. Taras Gerya, a professor of Earth sciences, remains cautious, suggesting that other processes could produce similar observations. He proposes an alternative theory, where Earth’s lithosphere behaves like a ‘squishy’ or semi-rigid layer rather than a fully rigid plate.
However, Simon Lamb, an associate professor of geology, finds the evidence persuasive, stating that it is difficult to envision such large displacements without subduction.
Ultimately, this new discovery provides crucial insights into the evolution of our planet, challenging existing theories and further fueling the ongoing scientific debate.
