In a strange corner of our solar system, there is two amorphous extraterrestrial masses. They are the size of continentsand they are thought to spend their time waiting for food to fall on them, which they then simply absorb. Its natural habitat is even more atypical than its diet. You could call it “rocky”: all around, exotic minerals of unknown shades and shapes. It is otherwise fairly barren, except for a shimmering sea in the distance, so huge that it contains as much water as all the Earth’s oceans combined.
Every day, the “time” is the same: a few 1827°C, and its pressure in some areas is about 1.3 million times that of the Earth’s surface. In this overwhelming environment, atoms warp and even the most familiar materials begin to behave eccentrically: rock is flexible like plastic, while oxygen behaves like metal.
But this burning place it’s not left on an alien planet, and these masses aren’t strictly wild animals He is, in fact, on Earth, only deep within it.
The environment in question it’s the lower mantle, the layer of rock that sits just above the planet’s core. This coat, largely solid, it’s another worlda swirling place dotted with a kaleidoscope of crystals, from diamonds (of which there are about a quadrillion tons) to minerals so rare that they do not exist on the surface of the planet.
In fact, the most abundant rocks in this layer, bridgmanite and davemaoite, are largely a mystery to scientists. They need the clean ultra-high pressures inside the planet to grow and they collapse if introduced into our realm.
We can only see them in their natural form when they remain trapped in the diamonds that reach the surface. And even then, it’s impossible to know what they actually look like inside the Earth, because their physical properties are so different at the pressures under which they normally exist.
For its part, this distant “ocean” does not even contain a drop of liquid. It is made from water trapped in the mineral olivine, which makes up over 50% of the upper mantle. At deeper levels it transforms into indigo blue ringwoodite crystals.
“At these depths, the chemistry changes completely”, explains Vedran Lekić, associate professor of geology at the University of Maryland (USA). “As far as we know, some minerals become more transparent,” he says. But these are those amorphous masses that most intrigue geologists around the world.
In 1970, the Soviet Union embarked on one of the most ambitious exploration projects in human history: it attempted drill as deep as possible into the earth’s crust. This solid layer of rock, which overlies the mostly solid mantle and possibly the partially molten core of the Earth, it is the only part of the planet that has never been seen by human eyes. Nobody knew what would happen if they tried to go through it.
In August 1994, the Kola super-deep well, located in the middle of an inhospitable expanse of arctic tundra in northeastern Russia, reached staggering depths, extending some 12,260 meters underground. Initially, the team leading the project made predictions about what they expected to find, specifically that the Earth would warm up by one degree for every 100 meters traveled towards its center.
However, it soon became apparent that this was not the case: in the mid-1980s, when they reached 10 km, the temperature was already 180°C, almost double what was expected. But then the drill jammed. In these extreme conditions, the granite was no longer drillable: it behaved more like plastic than like rock. The experiment has stopped and no one has managed to cross the threshold of the crust to date.
“We know much less about the Earth’s mantle than we know about outer space. -which we can observe with telescopes-, because everything we know is very, very indirect”, explains Bernhard Steinberger, researcher in geodynamics at the University of Oslo (Norway).
Next, how do you study an environment you can’t see or one that is not accessible, where even the chemical properties of the most common materials are distorted beyond recognition? It turns out there is another way.
Seismology consists in studying the energy waves produced by the sudden ground movement during massive events such as earthquakes. Among them are the so-called “surface waves”, which are superficial, and the “internal waves”, which pass through the interior of the Earth.
To capture them, scientists use instruments against earthquakes who seek to detect and examine anything that manages to break through. By analyzing the different wave patterns, they can begin to piece together what might be happening hundreds of miles underground. It is these characteristics that allowed the Danish geophysicist Inge Lehman make an important discovery in 1936.
seven years ago, a great earthquake in new zealand led to a surprising seismic result: a type of internal wave, which can pass through any material, managed to pass through the Earth, but had been “bent” by an obstacle on the way. And, another type of wave, which cannot pass through liquids, could not pass.
This overturned the long held belief that the core was completely solid and led to the modern theory that there is a solid interior wrapped in a liquid outer shell, a sort of inverted bogeyman, so to speak.
Over time, the method was perfected and allowed visualize the hidden depths of the Earth in three dimensions, “using the same techniques as computed tomography” that are used in medicine, says Lekić. Almost immediately, this led to discovery of the two amorphous masses of the Earth. calls “large provinces with low cutting speeds” (LLSVPS, for its acronym in English), are two colossal regions, where seismic waves meet resistance and slow down.
One of them, called “Tuzo”it is found under africa; the other, “Jason”is under the Pacific Ocean. As with the Earth’s core, these areas are clearly different from the rest of the coat and they are among the tallest structures on the planet. They are thousands of kilometers wide and occupy 6% of the volume of the entire planet.
Estimates of their height vary, but it is believed that Tuzo measures up to 800 km in altitude, which is equivalent to about 90 Everests stacked on top of each other. For his part, Jason could span 1,800 km, which corresponds to about 203 Everests.
Their misshapen bodies cling to the Earth’s core, like two amoebas to a speck of dust. “There is 100% certainty that these two regions are, on average, slower [en términos de la rapidez con que las ondas sísmicas se mueven a través de ellas] than the surrounding region. It’s not up for debate,” says Lekić. And add, “The problem is that our ability to see in that region is blurry.”.
Besides how titanic their forms are, almost everything else about them remains uncertain, including how they were formed, what they are made of and how they could affect our planet.
The scientists know that something is going on there and they are trying to figure out exactly what, because they believe that understanding them would help unravel some of the most enduring mysteries in geology, for example how the Earth was formed, the final fate of the “ghost” planet Theia and the unexplained presence of volcanoes in certain parts of the world. They could even shed light on how the Earth is likely to change over the next few millennia.