The Earth's core is slowing down its rotation and is rotating in the opposite direction to that of the surface. It was announced in Nature Geoscience as a result of the study of two Chinese scientists, Yi Yang and Xiaodong Song, of the Institute of Theoretical and Applied Geophysics of Peking University.
Rotation changes in the Earth's inner core can have several effects. The recently published study is based on the analysis of about 200 earthquakes that have occurred in the South Sandwich Islands in recent decades, starting in the 1960s.
These are double earthquakes, they have a common origin and produce identical waves. Even if the waves produced are the same, the stations in Alaska, therefore near the North Pole, have detected anomalies that can be explained by the fact that the nucleus rotates faster than the rest of the planet.
Comparing the results with those of 2009, it has been seen that the earth's core rotates more slowly and towards the west today. The anomaly of the rotation of the inner nucleus causes alterations of the gravitational field and the magnetic field.
It also causes surface deformations that change sea level, with possible consequences also on global temperature. Scientists explain that the rotation of the Earth's core depends on two factors: the Earth's magnetic field and gravitational attraction.
The magnetic field tends to produce a rotation identical to that of the Earth, while the gravitational attraction pushes the nucleus to rotate in the opposite direction. It is therefore probable that the oscillation of the rotational motion depends on the inversion of the earth's magnetic field.
It has already happened that the rotation of the earth's core has changed. In the early 1970s the core was not rotating, then it gradually began to rotate eastward, until it exceeded the speed of the crust. Then it started to slow down until between 2009 and 2011 it almost stopped.
Scientists have now discovered that the rotation is to the west, that is, opposite to the direction of Earth's rotation, and the speed is decreasing. The earth's core is subjected to a double rotation. The inner core rotates eastward at a faster rate than the rest of the planet.
The outer one instead rotates to the west at a slower speed than the rest of the planet. It is a discovery that dates back to the 1990s, when scholars identified that the inner sphere of the nucleus rotated at a faster rate than the Earth.
In 2009 it was discovered that the core's rotation had slowed down to achieve perfect synchrony with the Earth. The new study today tells us that this slowdown will continue until it stops altogether. It has also been discovered that the rotation of the nucleus is not always in the same direction.
About 70 years ago the core rotated in the same direction as the Earth, while in recent years the inner core has started to slow down and rotate in the opposite direction. In 2005 it was revealed that the nucleus makes one more revolution every 900 years than the rest of the planet.
The reason for this behavior depends on the tides and the distance from the moon, which slow down the surface speed of the earth's crust. This means that the days, in recent years, are a thousandth of a second shorter than in 1970.