Ancient Pilbara rocks speak of Earth’s first continents

A new study of the famous iron-red rocks in Western Australia’s arid Pilbara region has revealed that the formation of Earth’s first continents occurred in a different way than originally thought.

The research, published in the journal Nature, sought to understand how the granite that made up the Earth’s earliest continents at the end of the Archaean eon (some 2.5 billion years ago) was formed. Critically, the researchers wanted to find where the water required for the granite’s formation came from.

To understand what Earth’s early history may have been like, the researchers tested the variation of oxygen isotope composition of zircon and compared this with the geochemistry of the rocks from Pilbara.

They found that the water in the type of granite present could not have come from the sky.

The study proposes that rather than coming from above, the water came from hydrated near-surface basalt rocks that were circulated into the Earth’s mantle through the process of overturn of the crust.

If this is correct, it means that rock formation processes in Earth’s early history were incredibly different from today.

Under these strange conditions, this mantle water may have been instrumental in forming the continents during Earth’s early years.

The study was a collaboration between Curtin University, The University of Western Australia, Geoscience Australia, and the Geological Survey of Western Australia.

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Further reading

• Plate tectonics: the hidden key to life on Earth
• Turbulent mantle nudges Earth’s crust
• How planetary forces shape Earth’s surface