Plate tectonics fired up at least 3 billion years ago, study of ancient rocks in Australia indicates

Scientists may have discovered the world's oldest arc-slicing fault in Northwestern Australia's remote deserts. The finding demonstrates that plate tectonic processes were operational at least 3 billion years ago, fueling the ongoing scientific debate.

"This study clearly demonstrates horizontal plate movements before 3 billion years ago," study co-author Timothy Kusky, director of the Center for Global Tectonics at the China University of Geosciences, told Live Science.

In the new study, published July 15 in the journal Geology, researchers revealed that around 3 billion years ago, large, city-size rock blocks moved horizontally past each other by at least 19 miles (30 kilometers). The patterns resemble what geologists call arc-slicing transform faults, seen in active volcanic arcs like the Andes and Sumatra. If the findings are correct, these battered rocks might 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, shifting continents, and seismic upheavals. Yet pinpointing the origins of this fundamental process remains a contentious debate.

Related: Earth's plate tectonics fired up hundreds of millions of years earlier than we thought, ancient crystals reveal

Models indicate that early Earth had less-developed convection currents necessary to drive plate tectonics, suggesting that a thick and rigid outer crust formed a "stagnant lid," limiting dynamic horizontal movements. While magma bodies may have risen and solidified, rigid 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 into individual tectonic plates.

Some scientists argue plate tectonics started in the Hadean, over 4 billion years ago. Others believe the primitive "single lid" or "stagnant lid" dominated early Earth until about 1 billion years ago.