4-Billion-Year-Old Remnants of Earth’s Crust Found Below Australia, Give Clues About the Formation and Evolution of Continents

A new study conducted in Australia has led to the identification of the deep remnants of our planet's primordial crust.

Understanding the History of Continental Crust

The Earth is believed to be born around 4.5 billion years ago. To understand its formation and evolution, scientists rely on rocks as well as the minerals they are made of.

For instance, the ancient crust of Australia is important in understanding the young Earth since it gives clues as to how the continental crust formed and evolved. The oldest rocks found in Australia are also considered some of the oldest on Earth. Found in the Murchison district of Western Australia, they have been dated to roughly 4 billion years old.

The continental crust is the outermost layer of the Earth's lithosphere, forming the landmasses where we live. It also supports ecosystems and provides important resources for living organisms.

Exploring the ancient continental crust, however, is not an easy task. This is due to the fact that most of it is buried deep beneath the Earth, or has been modified intensely by the environment. Fortunately, there are some exposed areas which allow researchers to observe the ancient crust directly.

Remnants of the Past

In a recent investigation, a team of experts has found a 4-billion-year-old chunk of Earth's crust as big as Ireland lurking beneath Western Australia near Collie, south of Perth. Led by Maximilian Droellner from Curtin University in Australia, the study suggests that something special might have occurred in that moment of our planet's history.

The piece of ancient crust lies near the area where the oldest minerals on the planet have been found. Known as zircons, the tiny minerals were found in Australia's Jack Hills and date back 4.4 billion years. These minerals were able to survive even when the rocks that once kept them have eroded away.

Geochemical analysis of the sediments near this region suggests that there could be older crust lying under newer rocks at the surface. To confirm this theory, Droellner and his colleagues test the zircons in sediments found in the Scott Coastal Plain. These sediments erode out of deeper layers of rocks on the Australian continent.

The zircons were vaporized with powerful lasers before being analyzed for the radioactive elements trapped over billions of years. The relative amounts of each isotope indicates how long the elements have been decaying, and thus provide an estimate of the age of the zircons.

The dating revealed that the rocks holding these minerals formed sometime between 3.8 billion and 4 billion years ago. Meanwhile, Earth-orbiting satellites helped gain insight into the location where these minerals likely came from.

It was found that the old chunk of crust covers an area of about 38,610 square miles (100,000 square kilometers). It is buried tens of kilometers below the surface, with its boundary associated with iron and gold ore deposits. This suggests the significance of this ancient crust in the formation of rocks and minerals in Western Australia.