Since the 1970s, the discovery of two giant structures inside the Earth has baffled scientists. They are located on opposite sides of our planet and their size may be compared to continents. Each of these structures is almost 100 times bigger than Mount Everest and is located at the core of the Earth, at a depth of 2900 km. Seismic studies show that the discovered formations have a different composition than the rest of the Earth’s mantle.
The structure, known as an ultralow-velocity zone (ULVZ), is located on the boundary between Earth’s superheated, molten core and the solid mantle, lying directly underneath the volcanic Marquesas Islands in French Polynesia in the South Pacific, according to a study published in the journal Science.
The discovery was made by researchers at the University of Maryland, Johns Hopkins University, and Tel Aviv University, Israel. They reported that the system used for this detection was originally developed to analyse distant galaxies, but ended up uncovering a mystery inside the Earth.
Scientists were able to detect the structures by analysing data on seismic waves that can reveal hidden underground structures as they travel across the planet.
These seismic waves, which are generated by earthquakes, travel thousands of kilometres below the surface, but as the material they pass through varies in density, temperature, or composition, the waves change speed, bend, or scatter, producing echoes that scientists can detect using instruments known as seismometers.
Using this data, researchers can create a picture of the rock below the surface and estimate its physical properties. In the latest study, the authors used a machine-learning algorithm called “Sequencer” to simultaneously analyse around 7,000 seismic wave records known as seismograms, generated by hundreds of 6.5-plus earthquakes that struck the Pacific region between 1990 and 2018.
To their surprise, the researchers found that nearly half of the diffracted waves had been scattered by three-dimensional structures near the core-mantle boundary, revealing new information about this sub-Pacific region of Earth.
The researchers detected particularly strong signals from beneath Hawaii and the Marquesas Islands, inducing the presence of large ULVZs that were defined as “dense patches at the core-mantle boundary.”
In the study, the scientists focused on echoes produced by a specific class of seismic waves known as shear waves. According to the United States Geological Survey, shear waves move the ground back and forth perpendicular to the direction the wave is moving. When viewing a single seismogram, it is difficult to distinguish echoes generated by diffracted shear waves from random noise. However, by looking at many recorded seismograms simultaneously, it can provide valuable information about the Earth’s interior.
Geophysicists have known about these structures anomalies (generally they call them Blobs) since the 1970s but are not much closer to understanding them today.
“They’re among the largest things inside the Earth,” University of Maryland geologist Ved Lekic told Eos reporter Jenessa Duncombe, “and yet we literally don’t know what they are, where they came from, how long they’ve been around, or what they do.”
This much is evident: The blobs begin thousands of miles below Earth’s surface, where the planet’s rocky lower mantle meets the molten outer core. One blob lurks deep below the Pacific Ocean, the other beneath Africa and parts of the Atlantic. Both are massive, stabbing up about halfway through the mantle and measuring as long as continents. According to Duncombe, each blob stretches about 100 times higher than Mount Everest; if they sat on the planet’s surface, the International Space Station would have to navigate around them.
Hollow Earth Hypothesis
In 1692, famous astronomer Edmund Halley hypothesized that there is empty space inside the Earth. He suggested that underground, there are two empty structures about 800 km far from each other. According to Halley, both structures are separated by the atmosphere and rotate at different speeds, so they have their own magnetic fields.
In 1818, this idea was picked by American scientist John Cleves Symmes Jr., who suggested that there are four empty spaces 1300 km thick inside the Earth. He said that one could reach them at the poles, which, in his opinion, contained the entrance to this underworld. Cleves Symmes even tried to organize an expedition to the North Pole, but he did not find enough funding, so the idea collapsed.
The US military, Admiral Richard E. Byrd, is a character who cannot be ignored in this context. He had been looking for entry into the underworld since 1926 when he flew over the North Pole. Three years later, he circled the South Pole. He made his first expedition in search of an entrance to the interior of the Earth in 1947. He traveled 2,750 km and, according to him, his goal was to achieve what was behind the pole, which he considered the “Great Mystery.”
Byrd probably knew that the Germans were also trying to open the entrance to the underworld. During the Nazi rule, the Thule Society was interested in this topic. The expedition plan that they prepared was also supported by Adolf Hitler, who ordered an entrance to Antarctica to be sought. Some people say that ultimately it was possible, but the discovery was classified.
In any case, many people say that the entrance to the hollow Earth exists. This is confirmed by satellite images of the North Pole taken in 1968. A hole is visible on them, which may indicate that this is the end of one of the empty structures. However, this conclusion has not been formally confirmed yet. Only in 2014, an expedition was planned in search of penetration into this underworld, but its organizers began to disappear under mysterious circumstances. For this reason, the company ended in failure.
For many years, the theory of the hollow Earth has been ridiculed as absurd, but the truth comes out gradually. A few years ago, it was revealed to the world that deep underground, there is a lot of water, more than in the oceans of the Earth.
Views expressed in this article are the opinions of the author and do not necessarily reflect the views of Collective Spark.
This article was originally published by How & Whys.