Bengaluru: Scientists used to think that Earth’s inner core rotated faster than the rest of the planet, but new findings suggest that around 2009, it slowed down like something out of a science fiction movie, and now spins more slowly. .
From the study of seismic data, it appears that the Earth’s inner core changes its rotation speed every 60–70 years on average.
This model of the rotation of the inner core may provide a possible explanation for other phenomena around the Earth that oscillate with similar time periods, such as variations in the magnetic field around the Earth, the global mean sea levelactivity in parts of the mantle (the solid part of Earth’s interior), and even the global mean Temperature,
The findings add to a growing body of work attempting to explain the rotation of the inner core.
This has been revealed in the study conducted by researchers Yi Yang and Xiaodong Song of Peking University in Beijing. published in the magazine nature geology on Monday. Sang was also included in this first paper which showed evidence of rotation of the inner core in 1996.
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layers under our feet
In the new study, the researchers studied earthquakes from 1995 to 2021, focusing on double or repeating earthquakes with similar waveforms detected at the same location. By analyzing changes in the timing and propagation of these signals, they can infer the rotation of the inner core, which is believed to move independently of the mantle and the rest of the planet.
They found that the super-rotation (faster rotation relative to the rotation of the mantle) of the inner core stopped around the year 2009. He said these changes were observed from different parts of the Earth and confirmed a planet-wide phenomenon. Thereafter, the inner core began to spin or rotate at a slower rate than the mantle.
The team also discovered a similar pattern in the early 1970s, which suggests that the change in speed occurred around that time as well.
The data agree with variations in Earth’s magnetic field as well as rotation, and the researchers say it adds further evidence for an inner core periodicity of 60–70 years on average.
Earth’s internal structure consists of four major layers: the outermost crust, the viscous but solid mantle beneath it, the liquid iron-nickel outer core, and the solid iron inner core.
The inner core is a solid ball about three-quarters the size of the Moon. It was discovered in 1936 when seismologists observed patterns in how earthquakes caused seismic waves to travel through the interior of the planet. Changes in the speed and direction of these waves suggest that the inner core must be solid.
This solid ball is encased in a liquid outer core and thus spins freely. The liquid core essentially isolates the inner core from the rest of the planet, allowing it to spin faster or slower.
The rotation of the outer liquid core generates the magnetic field around the Earth and the rotation of the inner core is subsequently caused by electromagnetic forces.
When the composition of the mantle and outer core differ, gravitational anomalies drive the rotation speed of the inner core up or down.
What else could it be?
Since we do not fully understand the Earth’s interior and cannot directly observe it, we gain knowledge about it from other effects we observe around us.
Discoveries from the 1960s began to suggest that the inner core might be undergoing a period of “super rotation”, while others indicated that this fast spin was par for the course.
Some models have suggested that – according to analysis of seismic waves from nuclear tests in the 1960s and 1970s – Earth’s inner core rotates more slowly than the mantle in the 1960s. Scientists believe that since the 1970s, the inner core has been rotating faster than the rest of the planet.
Since these models are built using seismic wave propagation, some scientists also suggest that uneven surfaces or deformations on the surface of the inner core, or changes at the inner-outer core boundary, may alter the propagation of these waves.
Changes in the speed of the inner core do not affect life on the surface of the Earth, but causes variations In other geophysical and climatic planetary phenomena. This also includes the length of a day.
Future models that build in more data and seismic observations over time will be able to better understand changes in the inner core’s rotation over the next few years.
(Editing by Nida Fatima Siddiqui)