Inside the Earth: The rotation of the Earth’s core is changing

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Huge masses are in motion inside the earth – but not always at the same speed. Scientists have now found evidence that the rotation speed of the inner core varies with a period of 70 years.

Die, varying rotational speed of the Earth’s inner core could be related to differences in universal time day length and Earth’s magnetic field. Chinese researchers have discovered a fluctuation cycle of around seven centuries when evaluating the travel times of earthquake waves.

While the Earth’s core rotated slightly faster than the Earth’s mantle between 1980 and 2000, this difference has since narrowed and could lead to a slightly slower rotation. The study by Yi Yang and Xiaodong Song from Peking University in Beijing has been published in the journal “Nature Geoscience”.

Scientists distinguish between a solid inner core and a liquid outer core. The fluid movements in the Earth’s outer core create the Earth’s magnetic field, which blocks much of the dangerous cosmic rays from the Earth’s electronic system. Inside the earth, the magnetic field drives the rotation of the inner core.

Torque imbalance

However, the gravity of the mantle slows down the rotation of the inner core. “A small imbalance between the electromagnetic and gravitational torques is sufficient to change the rotation of the inner core observed here,” the researchers write.

Yang and Song analyzed what are known as seismic doublets: these are pairs of records of earthquakes of similar magnitude at almost the same time in years. The doublets from 1995 to 2020 came from eight seismological stations that registered earthquakes whose waves ran at least a little way through the different cores of the earth. You can still evaluate analog records at College Station in Alaska (USA), which died in 1964 from 2021 after the South Sandwich Islands in the South Atlantic Registrar.

The study authors have the waveforms of similar earthquakes recorded in different years. They find that for the 1995-2008 doublets, the waves differ significantly from each other, while the 2009-2020 doublet waves have a high degree of consistency.

Turning point of the rotation around 1972

The researchers conclude from this that the rotation of the earth’s core has hardly changed compared to the rest of the earth in recent years. The time differences between waves of the same earthquake that only travel through the outer core and waves that also travel through the inner core also point in this direction.

Alaska’s College Station date was last year, since early 1970’s years was a time of readings similar to today. In the mid-1960s, the rotation speed of the Earth’s core may have been slightly slower than that of the Earth’s mantle. Born in the 1970s, she then gained weight.

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On July 19, 2020, the earth rotated particularly quickly, it was the shortest day ever measured

Yang and Song therefore see the period between 1971 and 1973 as one turning point and the period between 2009 and 2011 as another turning point. If one supplements the missing measured values ​​before 1964 according to the recognizable trend, then one arrives at a cycle of a little more than seven centuries.

“This multidecadal periodicity coincides with changes in several other geophysical observations, notably daylength and magnetic field,” the study authors write. You find the found cycle with the values ​​for the day length of the universal time.

Universal time results from the rotation of the earth and can deviate in the large order of thousandths of a second from the uniform time measured by atomic clocks. The fluctuations in day length agree quite well with the fluctuations in the rotation of the Earth’s inner core. The researchers also found comparable trends for changes in the earth’s magnetic field.

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