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A new geological study in the Pilbara suggests that the evolution of the Pilbara began much earlier than previously thought.

Honorary Research Fellow Dr MartinVan Kranendonk of The University of Western Australia's School of Earth and Environment took part in the study, published online this week in the prestigious journal Nature Geoscience. The study brings us closer to understanding more precisely the composition and timing of the formation of the primordial earth crust and helps unravel part of the earliest history of our planet.

This ancient history of Earth remains obscure because the oldest preserved terrestrial rocks are 4.03 billion years old, leaving a window of almost 500 million years after Earth's formation at 4.567 billion years with very little recorded history. Recent advances in Geochemistry allow us to decipher the isotopic signals that keep the memory of older rocks.

Relics of barely deformed and altered ancient rocks are present in some parts of the world, such as the Pilbara Craton. To go back in time and better understand the early history of our planet, the researchers looked at the North Pole Dome site of the Pilbara Craton which contains some of the oldest terrestrial rocks and fossils. The remnants provided the vital clues indicating some geochemical fingerprints of ancient lithosphere.

The team collected and analysed samples including volcanic, sedimentary and hydrothermal rocks. The results confirmed previous studies that showed the rocks are 3.49 billion years old. However, they were contaminated by much older crustal component during their formation. Geochemical modelling shows the crustal component to be at least 4.3 billion years old.

Until now, the physical remnants of such an old crust have not been found on the Earth's surface - except for rare zircon crystals which are preserved in another area of WA - the Yilgarn Craton. These crystals have revealed a surprising amount about early Earth conditions, but only tell one side of the crustal evolutionary story - that of granitic crust. The researchers show that there was another side to the early Earth story - a mafic crustal component.

The findings provide further evidence that the crust on Earth started to form between 4.3 and 4.5 billion years ago. This crust may represent a part of the early "skin" covering what is widely considered to have been a magma-ocean over early Earth.

The team was led by Research Associate Dr Svetlana Tessalina, of the Department of Earth and Planetary Sciences at Macquarie University. The team also included Prof. Pascal Philippot from the Institut de Physique du Globe de Paris, and colleagues from the Geological Survey of Western Australia and Switzerland.

For more information: https://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo772.html#top

Media references

Dr Martin Van Kranendonk (+61 8) 9222 3631

Janine MacDonald (UWA Public Affairs)  (+61 8)  6488 5563  /  (+61 4) 32 637 716