2023-06-12 16:08:38
Photo credit, Getty Images
- Author, Zaria Gorvett
- Role, BBC Future
It’s a dazzling summer day in Antarctica. With her icy eyelashes, Samantha Hansen contemplates the featureless landscape: a white wall, where the top is like the bottom, and where the ground merges with the sky.
In these disorienting conditions, with temperatures approaching -62°C, he spotted a favorable spot in the snow and pulled out a shovel.
Hansen finds himself in the inhospitable interior of the White Continent. Not in the scenic, slightly warmer Antarctica where cruises arrive, but in an unforgiving environment where flora and fauna don’t even venture.
As part of a team from the University of Alabama and Arizona State University, both located in the United States, he searched for hidden “mountain” ranges: peaks that no explorer has ever trod, whom the light of the sun has never illuminated.
These mountains are located in the depths of the Earth.
In 2015, researchers were in Antarctica to install a seismological station, a piece of equipment half buried in the snow that makes it possible to study the interior of our planet. In total, the team has installed 15 across Antarctica.
The mountain structures they revealed are quite mysterious. But Hansen’s team found that these ultra-low-velocity zones, or ULVZs, as they’re called, are likely widespread.
“We found evidence of ULVZ everywhere,” says Hansen. The question is to know what they are. And what are they doing inside our planet?
A mysterious story
Earth’s strange inner mountains appear at a critical location, between the planet’s metallic core and the rocky mantle that surrounds it.
As Hansen’s team points out, this abrupt transition is even more drastic than the change in physical properties between solid rock and air. It has intrigued experts for decades.
Although this “boundary” between the core and the mantle is located thousands of kilometers from the surface of the Earth, there is a surprising influence between its depths and our own world.
Photo credit, Getty Images
Earth’s interior mountains sit between the planet’s metallic core and the rocky mantle that surrounds it.
It’s thought to be a sort of graveyard for ancient pieces of the ocean floor, and may even be the source of volcanoes in unexpected places, like Hawaii, by creating very hot lanes in the crust.
The detection of Earth’s deep mountains began in 1996, when scientists explored the core-mantle boundary deep in the central Pacific Ocean.
To do this, they studied seismic waves created by massive shaking of the ground, usually earthquakes, although nuclear bombs can produce the same effect.
These waves pass through the Earth and can be picked up by seismic stations located elsewhere on the surface, sometimes more than 12,742 km from their point of origin.
By examining the paths of the waves, including their refraction by different materials, scientists can piece together an image of the planet’s interior that looks like an x-ray.
Examining the waves generated by 25 earthquakes, the researchers found that they inexplicably slowed down as they reached a jagged area at the boundary between the core and the mantle.
What can they be?
This vast, otherworldly mountain range was highly variable: some peaks reached 40 km into the mantle, 4.5 times the height of Everest, while others were only 3 km high.
Since then, similar mountains have been discovered in scattered locations around the core. Some are particularly large: One monstrous specimen occupies a 565-mile (910 km) wide area beneath Hawaii.
Photo credit, Getty Images
However, to this day, no one knows how they got there or what they are made of.
One theory is that the mountains are parts of the lower mantle that have become overheated due to their proximity to the Earth’s glowing core.
If the mantle can reach 3,700°C, this temperature is relatively low: the core can reach temperatures of 5,500°C, which is not very far from the temperature at the surface of the Sun.
It has been suggested that the hottest parts of the boundary between the core and the mantle might partially melt, which geologists consider to be the ULVZ zone.
Another theory indicates that the mountains of deep Earth might be made of a subtly different material than the mantle that surrounds them.
Incredibly, it is thought to be the remnants of ancient oceanic crust that disappeared into the depths and eventually sank over hundreds of millions of years to be deposited just above the core .
Photo credit, Getty Images
Most of the earth’s crust is made of basalt, which might also be the material behind the mysterious mountains of deep Earth
In the past, geologists have looked for clues in a second puzzle.
Deep Earth mountains are usually found near other mysterious structures: huge bubbles or large low shear velocity zones (LLSVP).
There are only two: an amorphous bulge called “Tuzo” under Africa and another known as “Jason” under the Pacific.
They are believed to be truly primitive, possibly billions of years old. No one knows what they are or how they got there, but their proximity to the mountains has led to speculation that they are somehow related.
One explanation for this link is that it all started with tectonic plates sliding through the Earth’s mantle and sinking down to the boundary between the core and the mantle. They then slowly expanded to form a variety of structures, leaving a trail of mountains and spots.
If so, that would mean that both types of plates are made of ancient oceanic crust: a combination of basalt and sediment from the ocean floor, transformed by intense heat and pressure.
But the existence of mountains deep beneath Antarctica might contradict this hypothesis, Hansen suggests: “Most of our study region, the Southern Hemisphere, is quite remote from these large features.
A cold search
To set up their seismic stations in Antarctica, Hansen and his team traveled to the appropriate sites in helicopters and small planes, placing the equipment in the snow, sometimes near the shore, under the curious gaze of penguins and inland otters.
It only took a few days to get the first results.
Instruments can detect earthquakes almost anywhere on the planet: “If it’s big enough, we can see it,” Hansen says, and the opportunities abound.
Photo credit, Getty Images
Seismograph stations have detected these mysterious mountains inside the Earth
The US National Earthquake Information Center records regarding 55 earthquakes per day around the world.
Although mountain ranges have been identified in the depths of the Earth before, no one had looked for them under Antarctica.
Antarctica is not near any of the Mystery Points, nor a recently plunged tectonic plate. However, to the team’s surprise, they found some at all the sites they sampled.
Mountains were previously thought to be scattered near spots occupied by spots. But Hansen’s results suggest they might form a continuous “blanket” enveloping the Earth’s core.
Verification of this idea will require much more research: before the study of Antarctica, only 20% of the boundary between the core and the mantle had been verified.
“But we hope to fill this gap,” says Hansen, who explains that it also depends on the development of new techniques to identify smaller structures.
In some areas, ULVZ structures look more like thin plateaus than mountains, so it is not yet possible to see the entire layer.
However, if the mountains are really that extensive, it would have implications for both their composition and how they relate to larger blob structures.
Could the smaller, mountain-sized remnants of plate tectonics really have ended up scattered so far away from the large blobs?
Whatever our findings, it’s oddly appropriate that the icy, alien landscape of Antarctica gives us clues to the strange, superheated mountains that lie deep within the Earth.
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