Study from China: Movements in the Earth's interior could affect day length

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Illustration: Structure of the Earth's core

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The earth revolves around the sun and around itself – but there is also movement inside the planet.

Researchers have found out that this movement is not always the same speed.

The fluctuating rotation speed of the inner core of the earth could explain fluctuations in the length of the days of universal time.

Chinese researchers have discovered a fluctuation cycle of around seven decades when evaluating the travel times of earthquake waves.

Between 1980 and 2000, the earth's core rotated slightly faster than the earth's mantle, since then the difference has become smaller.

The study by Yi Yang and Xiaodong Song from Peking University in Beijing has been published in the journal »Nature Geoscience«.

Specialists distinguish between the solid inner core and the 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 radiation.

Inside the earth, the magnetic field drives the rotation of the inner core.

However, the gravity of the mantle slows down the rotation of the inner core.

"A small imbalance between the electromagnetic and the gravitational torque is sufficient to change the rotation of the inner core observed here," the researchers write.

Influence on world time?

Yang and Song analyzed what are known as seismic doublets: pairs of records of similar-magnitude earthquakes at almost the same location in different years.

The experts compared the waveforms of the shocks recorded at different points in time.

In earthquakes that occurred in similar locations from 1995 to 2008, they found that the waves differed significantly.

In contrast, the experts found a high degree of agreement with the corresponding data from 2009 to 2020.

From this they conclude 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.

The researchers compared the cycle they found with the values ​​for the length of days in universal time.

Universal time results from the rotation of the earth and can deviate by the order of a thousandth of a second from the uniform time measured with atomic clocks.

The fluctuations in day length agree quite well with the fluctuations in the rotation of the Earth's inner core.

The researchers found comparable trends for changes in the earth's magnetic field.

ani/dpa