Last updated October 25, 2018 at 1:35 pm
A remote area of Australia showcases the Earth’s earliest stable crust.
A gorge at Karijini National Park shows off the rocks of the Pilbara craton. Credit: iStock
The rocks in a section of the remote East Pilbara region of Western Australia have been found to date to between 3.6 and 3.4 billion years ago – substantially before plate tectonics began to shape much of the planet.
In research published in the journal Nature Geoscience, a team led by Daniel Wiemer of the Queensland University of Technology reports that the rocks that form the Pilbara craton – an ancient, geologically stable section of the Earth’s crust – were formed through three “gravitational overturn” events, each lasting about 100 million years.
The craton formed during a period known as the early Archaean eon, which began with the first formation of the Earth’s crust about four billion years ago, and ended about 1.5 billion years later.
Formation of the Pilbara craton
During this period, the Earth’s mantle is thought to have been at its hottest and the crust immediately above it very unstable.
Using a mixture of uranium-lead dating and thermodynamic modelling, in association with previous geological studies, Wiemer and his colleagues concluded that the distinctive granite rocks of the craton formed through the interaction of minerals and heat.
During the process, denser materials sank slowly down into the unstable and viscous mantle, while lighter elements were pushed upwards, resulting in the telltale stripes that characterise ancient rocks.
The scientists estimate that each of these cycles took 100 million years to complete and that the region underwent a trio of them.
Transition to plate tectonics
The process came to a halt at least 200 million years before the Earth’s crust became hard enough for plate tectonics to assume the primary role in shaping the landscape.
“A better understanding of Earth’s oldest stable crust is essential for evaluating how the planet transitioned to plate tectonics, the nature of the substrate on which early life formed and how the vast mineral resources that are found in early Earth cratons formed,” says co-author David Murphy.
The researchers suggest that similar triple-cycle evidence found for other cratons in India and Africa indicate that the early Earth rocks may have formed in line with a planet-wide “pulse”.
