When Jules Verne wrote Journey to the Center of the Earth more than 150 years ago, he imagined a land of glowing crystals, stormy seas, prehistoric animals, and giant mushrooms.
But what actually lies beneath our feet remains a mystery – even today we know more about Saturn’s rings than about the interior of our planet.
In the last 30 years, however, our understanding of the Earth’s inner core has expanded dramatically and has been shown to move and change for decades.
But while it was previously thought to rotate at a faster speed than the planet’s surface, a new study shows that it oscillates, moving back and forth more than a mile every six years.
The cycle may explain the variations in the length of days that have been shown to fluctuate steadily over the last few decades.
USC researchers have identified a six-year cycle of super- and subrotation in the Earth’s inner core, which contradicts previously accepted models that suggested that it is constantly spinning faster than the planet’s surface.
FOUR LAYERS OF PLANET EARTH
Bark: At a depth of 70 km, this is the outermost layer of the Earth, covering both oceanic and terrestrial areas.
Mantle: Going down to 2890 km with the lower mantle, it is the thickest layer on the planet and is made of silicate rocks, richer in iron and magnesium than the crust above the head.
Outer core: Continuing from a depth of 2890-5150 km, this region is made of liquid iron and nickel with traces of lighter elements.
Inner core: Going down to a depth of 6370 km in the very center of the planet Earth, this region is believed to be made of solid iron and nickel. But this new study suggests it contains both mushy and solid iron.
The Earth’s inner core is a hot, dense ball of solid iron the size of Pluto – and hot as our sun.
It is impossible to observe directly, which means that researchers must rely on indirect measurements to explain the model, the speed and the reason for its movement and changes.
The U.S. team used seismic data from 1969 to 1974 to create a computer model of nuclear motion.
The simulations confirmed the displacement of the Earth’s surface compared to its inner core, according to scientists for 20 years.
However, this contradicts previous theories that suggest that the speed of rotation is consistently faster than the planet’s surface.
“The inner core is not fixed – it moves under our feet and seems to move back and forth a few kilometers (1.25 miles) every six years,” said lead author Professor John Videle of the University of Southern California.
A study published in 1996 was the first to suggest that the inner core rotates faster than the rest of the planet – also known as super-rotation – by approximately 1 degree per year.
Prof. Videil’s subsequent discoveries confirmed the idea that the inner core rotates super, albeit at a slower speed.
Using data from the LASA (Large Aperture Seismic Array), a facility of the US Air Force in Montana, Prof. Widel found that the inner core rotates approximately 0.1 degrees per year.
Laboratory staff have developed a new beamforming technique to analyze waves generated by Soviet underground tests of nuclear bombs from 1971 to 1974 in the Arctic archipelago of New Earth.
The latest results came when they applied the same methodology to a pair of earlier atomic tests under Amchitka Island in the Alaska-Milou archipelago in 1969 and Cannikin in 1971.
Measuring the pressure waves resulting from the nuclear explosions, they found that the inner core had been reversed, rotating at least one-tenth of a degree a year.
“Our latest observations show that the inner core rotated a little slower than 1969-71 and then moved in the other direction from 1971-74,” said Professor Videle.
“We also note that the length of the day has increased and shrunk as expected.
“The coincidence of these two observations makes the oscillation a plausible interpretation.”
Because the Earth’s inner core is so inaccessible, researchers had to rely on the only means available to study the innermost Earth – seismic data (image).
Map A shows the location of the LASA (triangle) and the two pairs of nuclear tests (stars). B ans C show the distribution of the predicted time shifts
This is the first time that the six-year fluctuation has been shown by direct seismological observation.
Using seismological data from atomic tests in previous studies, researchers have been able to determine the exact location and time of the seismic event.
“The idea that the inner core was fluctuating was a model that was there, but the community was divided on whether it was viable,” said Professor Videle.
“We went into this, expecting to see the same direction and speed of rotation in the earlier pair of atomic tests, but instead we saw the opposite.
“We were quite surprised to find that it was moving in the other direction.”
LASA was closed in 1978 and the era of US underground nuclear testing is over, which means that researchers will have to rely on relatively inaccurate earthquake data for future research in this area, even with the latest advances in the toolkit.
However, the study supports speculation that the inner core oscillates based on variations in day length – plus or minus 0.2 seconds in six years – and geomagnetic fields, both consistent with both amplitude and amplitude theory. and by phase.
Videle said the findings provide a compelling theory for many of the questions raised by the research community.
“One of the questions we tried to answer is whether the inner core is moving progressively or is it mostly locked compared to everything else in the long run?
“We are trying to understand how the inner core formed and how it moves over time – this is an important step in better understanding this process.”
The study is published in Science Advances.
THE LIQUID IRON CORE OF THE EARTH CREATES THE MAGNETIC FIELD
It is believed that the magnetic field of our planet is generated deep in the Earth’s core.
No one has ever traveled to the center of the Earth, but by studying the shock waves of earthquakes, physicists have been able to develop its probable structure.
At the heart of the Earth is what was thought to be its solid inner core, two-thirds the size of the Moon and made mostly of iron. However, this new study disputes this.
At 5700 ° C, this iron is as hot as the surface of the Sun, but the lubricating pressure caused by gravity prevents it from becoming liquid.
Around this is the outer core, which is a layer of iron, nickel and small amounts of other metals with a thickness of 1242 miles (2000 km).
The metal here is liquid due to the lower pressure than the inner core.
Differences in temperature, pressure, and composition in the outer core cause convective currents in the molten metal as the cool, dense matter sinks and the warm matter rises.
The Coriolis force caused by the Earth’s rotation also causes rotating vortices.
This flow of liquid iron generates electric currents, which in turn create magnetic fields.
The charged metals passing through these fields continue to generate their own electric currents and so the cycle continues.
This self-sustaining contour is known as a geodynamic.
The spiral caused by the Coriolis force means that the individual magnetic fields are approximately aligned in the same direction, and their combined effect creates a huge magnetic field that engulfs the planet.
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