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earth inner structure

New study attempts to explain the mystery of inner core of Earth

The movements of the innermost core of planet Earth are still a mystery. Beneath the surface of the planet, there is an extremely hot inner core which is surrounded by a molten liquid outer core. It is detached from the upper mantle and crust covering it. This arrangement has led to several questions, one of which is super-rotation. The inner core of the Earth is not connected to the mantle being separated by the fluidic outer layer. So this poses a question of its effect on Earth’s rotation.

Super rotation suggests that the inner core spins at a rate which is different to the rate of rotation of Earth i.e a complete rotation every 24 hours with respect to Sun. The inner core’s rate has been the subject of debate among scientists for a long period of time. Fresh analysis by John Vidale, a seismologist from the University of Southern California gives a new estimate for consideration. The study appears in the Geophysical Research Letters journal.  He examines the backscattered seismic waves which were detected with the help of nuclear tests carried out by the Soviet Union in Novaya Zemlya archipelago, northern Russia in 1971 and 1974. Several seismic stations including Large Aperture Seismic Array(LASA) which is the first large seismic array in the world detected the force of the blasts as the explosions were carried out. Vidale calculated that the inner core rotated nearly 0.07 degrees greater than the remaining planet during 1971 and 1974 with the help of LASA data and inner core motion based on the seismic waves. 

Maya Wei-Haas explains for the National Geographic that if the rate is correct, it means for a particular spot on the surface of Earth, the inner core would have moved 4.8 miles further over the course of one year. 

In 2000, Vidale estimated the rate to be 0.15 degrees per year with the help of the same nuclear test data which is much faster than the present estimation. Vidale explains that the latest estimate is accurate due to the improvements in data correction and interpretation. 

This is still a theoretical field as it is not possible to study the inner core from a closer perspective, hence this is also a reason for the rates differing. Super rotation came up in the 1970s but the proper modelling and seismic evidence came up in 1990s. Another study explained that the variations might be due to the differences in the surface of the inner core itself. More clarity in the results will only come up with more rigorous studies taken up by scientists. 

Journal Reference: Geophysical Research Letters