Researchers from The University of Western Australia and the Queensland University of Technology have unveiled how the Australian continent formed and evolved long before the evolution of the Earth’s present day tectonic plates.
This improved understanding of the Earth’s ancient crust could lead to a more accurate explanation of how past geological events occurred on the Earth and how planets evolved.
The study, published today in Nature Geoscience, was based on the researcher’s discovery of the, so far, oldest documented rock populations in the East Pilbara of Western Australia, a natural laboratory for early Earth research.
The research team carried out uranium-lead dating of minerals and found that the rocks formed 3.6-3.4 billion years ago – a time when Earth’s mantle is predicted to have reached peak temperatures during the planet’s evolution.
Field observations and chemical analyses of the rocks revealed that the ancient Earth’s crust, exposed in the East Pilbara, underwent a gravitational overturn shortly after its formation. Events such as these are the result of gravitational instabilities of the crust, resulting from the volcanic properties of a hot early Earth.
The research team found that at least three successive overturn events, following 100 million-year-cycles, affected the ancient East Pilbara crust before modern plate tectonic processes commenced at around 3.2 billion years ago.
These events are thought to be responsible for the progressive thermal and chemical mixing of the ancient crust, ultimately allowing the emergence of a stable continent with the ability to sustain plate tectonic processes.
A better understanding of the occurrence of these events may be critical to predicting the subsequent onset of plate tectonic processes, as well as improve understanding about the evolution of other terrestrial planets.
Lead author Dr Daniel Wiemer, from UWA’s Centre for Exploration Targeting, said the research was based on the oldest crustal rock association so far documented in the East Pilbara.
“The study demonstrates the distinct formation and evolution through cyclic gravitational overturns of the ancient crust during predicted peak temperatures of the Earth’s mantle,” Dr Wiemer said.
“We were able to reconstruct the formation of granite-like rocks and their subsequent exhumation, erosion and sedimentation during the oldest recognised gravitational overturn.
“Our reproduction of this event holds critical insights into early Earth evolution and may inspire future research on other terrestrial planets.”
Next, the researchers hope to carry out further research in the East Pilbara and on other early Earth crustal fragments found around the world.
Dr Daniel Wiemer (School of Earth Sciences, Centre for Exploration Targeting) (+61 4) 57 221 785
Jess Reid (UWA Media and Public Relations Advisor) (+61 8) 6488 6876