Context: The spin of Earth’s inner core may have slowed, with the heart of the planet now rotating at a slightly more sluggish clip than the layers above.

• A recent study says that the inner core of Earth seems to have stopped spinning in the same direction as the rest of the planet.

Key Concept

• The planet’s solid inner core might rotate at a different rate than the rest of the planet, and that rate might be changing.

• The spin of Earth’s inner core may have slowed, with the heart of the planet now rotating at a slightly more sluggish clip than the layers above, new research finds.

• The slowdown could change how rapidly the entire planet spins, as well as influence how the core evolves with time.

About the study

• For the new study, published in the journal Nature Geoscience, scientists used a database of earthquakes to probe the behavior of Earth’s solid inner core over time.

• The inner core sits suspended like a ball bearing in the molten-metal ocean of the outer cor

• Because of this liquid cocoon, the “ball bearing” may not spin at the same rate as the rest of the planet.

• Over the years, some researchers have found that the core rotates slightly faster than the mantle and crust, a condition called “super rotation.”

• But it had been slowing down before coming in sync with Earth’s rotation around 2009, the study said

• In the new study, the researchers studied quakes from 1995 to 2021, with a focus on doublets or repeating quakes with similar waveforms detected at the same location. By analysing changes in the time and propagation of these signals, they could estimate the rotation of the inner core, which is believed to move independently from the mantle and rest of the planet.

• They found that the inner core’s super-rotation (faster rotation relative to the rotation of the mantle) stopped around the year 2009. They said these changes were observed from different parts of the Earth and confirmed a planet-wide phenomenon. Subsequently, the inner core began sub-rotation or rotating slower than the mantle

Earth  Interior

• The Earth’s inner structure consists of four major layers: the outermost crust, the viscous but solid mantle below it, the liquid iron-nickel outer core, and the solid iron inner core.

• The inner core is a solid ball that is about 3/4th the size of the moon. It was discovered in 1936 when seismologists noticed patterns in how seismic waves caused by earthquakes travelled through the interior of the planet. Changes in the speed and direction of these waves showed that the inner core must be solid.

• This solid ball is encased in the liquid outer core and thus spins freely. The liquid core essentially decouples the inner core from the rest of the planet, allowing it to rotate faster or slower.

• The rotation of the outer liquid core produces the magnetic field around the Earth and the rotation of the inner core subsequently occurs due to electromagnetic forces.

• When there are variations in the structure of the mantle and outer core, gravitational anomalies drive up or down the speed of the rotation of the inner core.

Core of the earth 

• It is the innermost layer surrounding the earth’s centre.

• The core is separated from the mantle by Guttenberg’s Discontinuity.

• It is composed mainly of iron (Fe) and nickel (Ni) and hence it is also called as Barysphere.

• The core constitutes nearly 15% of earth’s volume and 32.5% of earth’s mass.

• The core is the densest layer of the earth with its density ranges between 9.5-14.5g/cm3.

• The Core consists of two sub-layers: the inner core and the outer core.

• The inner core is in solid state and the outer core is in the liquid state (or semi-liquid).

• The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.

• Barysphere is sometimes used to refer the core of the earth or sometimes the whole interior.