Geologists have discovered mysterious giant structures hidden deep within the Earth.
We know less about the interior of the Earth than we do about the surface of the Moon.
No-one, not even a robot probe, has ventured deeper than a few miles into the Earth’s crust.
While we know that motion at the core of the Earth generates the magnetic field that protects us from deadly solar radiation, the science behind how this field is generated is not fully understood.
Even the theory of plate tectonics – the mechanism behind continental drift that causes earthquakes and volcanoes – was not generally accepted until after the First World War.
Now data from hundreds of major earthquakes has helped a team led by Doyeon Kim at the University of Maryland in the US discover a strange new structure beneath the Marquesas Islands in the South Pacific Ocean.
The structure, known as an ultra-low velocity zone (ULVZ), is about 620 miles in diameter and just under 16 kilometres thick, says Kim.
A similar, even larger structure exists beneath Hawaii.
These gigantic and mysterious structures are especially interesting because they date back to the period before Earth had a Moon.
These chunks of exotic material could even be the scars dating back to the titanic collision between the Earth and an unknown object the size of Mars that gave birth to the Moon over four billion years ago.
The intriguing anomalies deep within the Earth are revealed by the progress of seismic waves caused by earthquakes.
Kim’s team analysed seismograms produced by slow-moving shear (S) waves that follow earthquakes’ primary tremors (P-waves) along the boundary between the Earth’s mantle and its core.
These S-waves produce clearer signals for analysis.
Kim’s team used an algorithm called Sequencer to process the data from hundreds of earthquakes that occurred between 1990 to 2018.
The data offers unique insights into the deepest and oldest parts of our planet.
“This is very interesting because this might indicate that mega-ULVZs are special and may host primitive geochemical signatures that have been relatively unmixed since early Earth history,” Kim told Vice.
“We’re hoping that Sequencer will be able to basically let us use all of these diverse datasets and bring them together to look for these lower mantle structures systematically,” he said.
The deepest hole ever drilled is the the Kola Superdeep Borehole. It took Soviet scientists almost 20 years to drill 40,230ft-deep pit.
They found microscopic plankton fossils over four miles beneath the Earth’s surface.
Locals like to joke that the borehole is so deep you can hear the screams of souls tortured in Hell echoing up from its depths.
But even at that unimaginable depth, the drill was only about one-third of the way through the crust to the Earth’s mantle when the project was abandoned.
With tools like Sequencer, scientists will be able to look deep into the heart of our planet and discover the processes that shield life on Earth from deadly cosmic radiation.
“That is our vision going forward,” says Kim, “to answer more questions about the lower mantle in general.”