What is really under the deserts and savannahs of Australia, beyond what we see in nature documentaries? A new magnetic map has brought to light a gigantic structure hidden beneath the subsoil of the Northern Territory, a magnetic anomaly with a silhouette reminiscent of the outline of the country itself. The work, presented by national science agency CSIRO, offers key clues about the geological history of the continent and how we explore its resources without blindly opening the earth.

A magnetic “footprint” in the shape of a country

Researchers have named this structure the Australia Magnetic Anomaly, because on maps it appears as a kind of magnetic “shadow” in the shape of Australia, buried under the Northern Territory (Australia). This is a local variation in the Earth’s magnetic field caused by rocks rich in minerals such as iron, which become magnetized when they are formed and retain that signature for billions of years.

The interesting thing is that this signature works like the memory of an old hard drive. In this case, the “file” stores information about how deep rocks were formed and deformed, what tectonic stresses they endured, and which direction the field was pointing when the rock formed.

The first analyzes suggest that the western margin of the anomaly crops out in the Hatches Creek Formation, where sandstones and volcanic rocks appear deposited in shallow seas and river deltas between about 2,500 and 1,600 million years ago. That is, we are looking at very ancient remains of the Earth’s crust, even prior to many of the large continents as we know them today.

How they have “seen” something that is buried

The anomaly has not been discovered with a large excavation, but by reviewing an old trove of data. The team led by geoscientist Clive Foss reanalyzed information from the Bonney Well Survey, a 1999 campaign in which planes equipped with magnetometers flew over the Northern Territory following lines about 400 meters apart, measuring small variations in the magnetic field.

That data already existed, but the first images contained artifacts that distorted the finer details, especially when the magnetic structure coincided with the direction of flight of the planes. This is where the work of Aaron Davis comes into play, who developed a new processing algorithm to “box” the information and generate cleaner and more coherent maps.

According to Foss, this magnetic data allows us to “see through the ground and understand a geological architecture that would otherwise remain completely hidden.” Once the map was refined, the team has been able to identify boundaries between rock blocks, folds, faults and subtle magnetic layers that were previously lost in the noise.

The magnetic memory of a restless planet

The rocks that form this anomaly have two types of magnetism. On the one hand, an induced magnetization, which responds to the current magnetic field. On the other hand, a remanent magnetization, a “permanent memory” that records what the field was like when the rock was formed.

The problem is that the Earth’s magnetic field has changed direction many times and has completely reversed on numerous occasions throughout its history. Additionally, plate movements have shifted and rotated those blocks of rock. Unraveling that puzzle requires complex models and comparisons with other geological signals in the area. Scientists at Geoscience Australia and CSIRO have been fine-tuning these techniques for years to estimate the depth of magnetic sources and reconstruct the buried “landscape.”

What does this have to do with minerals and the environment?

At this point, you may be wondering what all this means for everyday life or for the ecological transition. In part, a lot.

The same aeromagnetic maps that reveal the Australia Magnetic Anomaly are the basis that companies and governments use to search for key minerals for renewable energy, such as copper or battery metals. This open data allows exploration campaigns to be better targeted and surveys concentrated in areas with the greatest potential, which can reduce unnecessary drilling and the impact on fragile ecosystems.

CSIRO emphasizes that since the 1990s, a good part of these geophysical databases have been freely accessible and used throughout the world, something that other countries are beginning to copy. That means that publicly funded science not only fuels new discoveries, it also helps plan more efficient mining, largely less invasive and aligned with the demand for minerals for clean technologies.

Of course, better information does not in itself guarantee responsible exploitation. This is where environmental laws, consultation with local communities and political decisions come in. But having a much clearer map of what is under our feet is an important step in deciding where it makes sense to extract and where it is better not to touch.

A natural laboratory under the desert

The Australia Magnetic Anomaly is, in essence, a natural laboratory that condenses billions of years of the planet’s history into a single structure. In the short term, researchers will continue refining the models and comparing magnetic data with outcrops such as those at Hatches Creek, where these deep rocks shyly appear on the surface.

Work remains to be done to translate all these signals into a detailed account of how the Australian continent was assembled and deformed. But the underlying message is clear. The better we understand the interior of the Earth, the more options we have to make the search for resources compatible with the protection of the territory and climate.

The official press release about this discovery has been published by CSIRO and can be consulted in the article in English “Geosurvey reveals hidden Australia Magnetic Anomaly”, available at CSIRO website.