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- Author: Zaria Gorvett
- Rolle, BBC Future
38 minutes ago
It’s a bright summer day in Antarctica. With her icy lashes, Samantha Hansen surveys the featureless landscape: a white wall where the top is like the bottom and where the ground merges with the sky.
In these confusing conditions and with temperatures nearing -62°C, he found a favorable spot in the snow and pulled out a shovel.
Hansen finds himself in the inhospitable interior of the White Continent. Not in scenic, slightly warmer Antarctica, where cruises arrive, but in a harsh environment where flora and fauna don’t even dare.
As part of a team from the University of Alabama and Arizona State University, both in the United States, he searched for hidden “mountain ranges”: peaks that no explorer has ever set foot on and that have never been illuminated by the sun’s light.
These mountains are deep in the earth.
In 2015, researchers were in Antarctica to install a seismological station, a device half-buried in the snow that makes it possible to study the interior of our planet. In total, the team has installed 15 throughout Antarctica.
The mountain structures they revealed are quite mysterious. However, Hansen’s team found that these so-called ultra-low-velocity zones (ULVZs) are likely to be widespread.
“We found evidence of ULVZ everywhere,” says Hansen. The question is to know what they are. And what are they doing on our planet?
A mysterious story
Earth’s strange inner mountains appear at a critical juncture, 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 fascinated experts for decades.
Although this “boundary” between the core and the mantle is thousands of kilometers from Earth’s surface, there is a surprising correlation between its depths and our own world.
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Earth’s inner mountains lie between the planet’s metallic core and the rocky mantle that surrounds it.
It’s thought to be a kind of graveyard for ancient bits of seafloor and possibly even the source of volcanoes in unexpected places like Hawaii, creating very hot tracks in the crust.
The discovery of Earth’s deep mountains began in 1996 when scientists probed the core-mantle boundary deep in the central Pacific.
To do this, they studied seismic waves produced by massive ground shaking, usually earthquakes, although atomic bombs can have the same effect.
These waves penetrate the earth and can be detected by seismic stations elsewhere on the earth’s surface, sometimes more than 12,742 km from their point of origin.
By studying the paths of waves, including how they refract through different materials, scientists can put together an image of the planet’s interior that looks like an X-ray.
Studying the waves produced by 25 earthquakes, researchers found that they inexplicably slowed as they reached a craggy area at the core-mantle boundary.
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.
Similar mountains have since been discovered at scattered locations around the core. Some are particularly large: one monstrous specimen spans an area 910 km wide beneath Hawaii.
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However, to this day no one knows how they got there or what they were made of.
One theory holds that the mountains are parts of the Earth’s lower mantle that have overheated due to their proximity to the Earth’s glowing core.
If the mantle can reach 3,700°C, that temperature is relatively low: the core can reach temperatures of 5,500°C, which is not very far from the temperature at the Sun’s surface.
It has been suggested that the hottest parts of the core-mantle boundary may partially melt what geologists consider the ULVZ zone.
Another theory suggests that the mountains deep within the Earth may be made of a slightly different material than the mantle that surrounds them.
Incredibly, these are believed to be remnants of ancient oceanic crust that disappeared into the depths and eventually sank over hundreds of millions of years, depositing just above the core.
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Most of the Earth’s crust is made of basalt, which could also be the material behind the mysterious mountains deep within the Earth
In the past, geologists looked for clues in a second mystery.
Deep mounds are usually found near other mysterious structures: giant bubbles or large low shear rate zones (LLSVP).
There are only two: an amorphous bulge called “Tuzo” under Africa and another called “Jason” under the Pacific.
They are believed to be truly primitive and 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 connection is that it all started with tectonic plates sliding through the mantle and sinking to the boundary between the core and the mantle. Then they slowly expanded and formed various 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 seafloor sediments transformed by intense heat and pressure.
But the existence of mountains deep beneath Antarctica may contradict this hypothesis, Hansen suggests: “Most of our study region, the southern hemisphere, lies quite distant from these large structures.”
A cold quest
To set up their seismic stations in Antarctica, Hansen and his team traveled to sites by helicopter and light aircraft and placed the equipment in the snow, sometimes near shore, under the curious eyes of penguins and river vipers.
It only took a few days to see the first results.
Instruments can detect earthquakes almost anywhere in the world: “If it’s big enough, we can see it,” says Hansen, and the possibilities are numerous.
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Seismograph stations have discovered these mysterious mountains in the earth’s interior
The US National Earthquake Information Center records about 55 earthquakes per day worldwide.
Although mountain ranges have been identified in the depths of the earth before, no one had looked for them in Antarctica.
Antarctica is neither close to any of the Mystery Points nor to a recently collapsed tectonic plate. To the surprise of the team, however, they found some at all the locations examined.
Mountains were once thought to be scattered near spots occupied by spots. However, Hansen’s results suggest that they could form a continuous “blanket” enveloping the Earth’s core.
Verifying this idea will require much more research: prior to exploration of Antarctica, only 20% of the core-mantle boundary had been verified.
“But we hope to close this gap,” says Hansen, who explains that developing new techniques to identify smaller structures is also important.
In some areas, ULVZ structures resemble thin plateaus rather than mountains, so the entire layer is not yet visible.
However, should the mountains really be that large, it would affect both their composition and their relationship to larger blob structures.
Could the smaller, mountain-sized remnants of plate tectonics really have ended up that far from the big clumps?
Whatever our findings, it is oddly fitting that Antarctica’s frigid, alien landscape gives us clues to the strange, superheated mountains that lie deep within the Earth.