Scientists have found evidence that the Earth’s inner core oscillates, which contradicts previous beliefs that it is constantly spinning faster than the planet’s surface.
The scientists identified a six-year cycle of super- and subrotation that affected the length of the day based on their analysis of seismic data.
The structure of the Earth is divided into layers, with the inner core in the center, followed by the outer core, the lower mantle, the upper mantle, the crust and the atmosphere. The inner core is the hottest part of the planet at around 10,000 ° F (5400 ° C), which is similar to the temperature of the sun’s surface!
It is believed to consist mainly of an iron-nickel alloy, the inner core is mostly a solid ball with a radius of about 760 miles (1220 km). It spins a little faster than the planet for a while, which is called super rotation.
Scientists at the University of Southern California (USC) have found evidence that the Earth’s inner core oscillates, which contradicts previously accepted models, which suggest that it is constantly spinning faster than the planet’s surface.
Their study, published today (June 10, 2022) in the journal Science Advances, shows that the inner core changed direction during the six-year period 1969-74, according to seismic analysis. Scientists say their pattern of inner core movement also explains the variation in day length, which has been shown to fluctuate steadily over the past few decades.
“From our findings, we can see the displacement of the Earth’s surface compared to its inner core, as humans have argued for 20 years,” said John E. Widel, co-author of the study and professor of Earth sciences at USC Dornsife College of Letters. , arts and sciences. However, 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. We also note that the length of one day increases and decreases, as expected.
“The coincidence of these two observations makes the oscillation a probable interpretation.
USC researchers have identified a six-year cycle of super- and under-rotation in the Earth’s inner core, which contradicts previously accepted models that suggested that it is constantly spinning faster than the planet’s surface. Credit: Edward Sotelo / USC
The analysis of atomic tests accurately determines the speed and direction of rotation
Our understanding of the inner core has expanded dramatically over the last 30 years. The inner core – a hot, dense ball of solid iron the size of Pluto – has been shown to move and / or change over decades. It is also impossible to observe directly, which means that researchers struggle through indirect measurements to explain the pattern, speed, and cause of movement and change.
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. Subsequent discoveries from Videal confirmed the idea that the inner core rotates super, albeit at a slower speed.
The layers and structure of the Earth.
Using data from the High Aperture Seismic Massif (LASA), a facility of the US Air Force in Montana, researchers Wei Wang and Vidale found that the inner core rotates slower than previously anticipated, approximately 0.1 degrees per year. The study analyzes waves generated by Soviet underground tests of nuclear bombs from 1971-74 in the Arctic archipelago of New Earth, using a new beam-forming technique developed by Vidale.
The new findings came when Wang and Videle applied the same methodology to a pair of earlier atomic tests below Amchitka Island in the Alaska-Milou archipelago in 1969 and Kanikin in 1971. Measuring compression waves from nuclear explosions, they found the inner core had the opposite direction, rotating at least one-tenth of a degree per year.
This latest study marked the first time that the well-known six-year oscillation was detected by direct seismological observation.
“The idea that the inner core was fluctuating was a model that was there, but the community was divided over whether it was viable,” Videal said. “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. “
Future research to dig deeper into why the inner core formed
Videal and Wang noted that future research will depend on finding accurate enough observations to compare with these results. Using seismic data from atomic tests in previous studies, they have been able to determine the exact location and timing of a very simple seismic event, Wang said. However, the Montana LASA was closed in 1978 and the era of US underground nuclear testing is over, which means researchers will have to rely on relatively inaccurate earthquake data, even with the latest advances in instruments.
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 phase theory. . Videle says the findings provide compelling theory for many of the questions raised by the research community.
“The inner core is not fixed – it moves under our feet and seems to move back and forth a few kilometers every six years,” said Videal. “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 to better understand this process.
Reference: “Seismological observation of the oscillating inner core of the Earth” by Wei Wang and John E. Vidale, June 10, 2022, Science Advances.DOI: 10.1126 / sciadv.abm9916
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