Global Geological And Climatic Events

Earth’s inner core rotating slower than surface: Study


From UPSC perspective, the following things are important :

Prelims level: Earth's interior

Mains level: Read the attached story


Earth’s inner core, a hot iron ball the size of Pluto, has stopped spinning faster than the planet’s surface and might now be rotating slower than it, research suggested.

A quick recap of Earth’s Interior


Structure of earth’s interior is fundamentally divided into three layers – crust, mantle and core.

[A] Crust

  • It is the outermost solid part of the earth, normally about 8-40 kms thick.
  • It is brittle in nature.
  • Nearly 1% of the earth’s volume and 0.5% of earth’s mass are made of the crust.
  • The thickness of the crust under the oceanic and continental areas are different. Oceanic crust is thinner (about 5kms) as compared to the continental crust (about 30kms).
  • Major constituent elements of crust are Silica (Si) and Aluminium (Al) and thus, it is often termed as SIAL(Sometimes SIAL is used to refer Lithosphere, which is the region comprising the crust and uppermost solid mantle, also).
  • The mean density of the materials in the crust is 3g/cm3.
  • The discontinuity between the hydrosphere and crustis termed as the Conrad Discontinuity.

 [B] Mantle

  • The portion of the interior beyond the crust is called as the mantle.
  • The discontinuity between the crust and mantleis called as the Mohorovich Discontinuity or Moho discontinuity.
  • The mantle is about 2900kms in thickness.
  • Nearly 84% of the earth’s volume and 67% of the earth’s mass is occupied by the mantle.
  • The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed as SIMA.
  • The density of the layer is higher than the crust and varies from 3.3 – 5.4g/cm3.
  • The uppermost solid part of the mantle and the entire crust constitute the Lithosphere.
  • The asthenosphere (in between 80-200km) is a highly viscous, mechanically weak and ductile, deforming region of the upper mantle which lies just below the lithosphere.
  • The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move (plate tectonics).
  • The discontinuity between the upper mantle and the lower mantleis known as Repetti Discontinuity.
  • The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.

[C] Core

  • 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 NIFE.
  • It constitutes nearly 15% of earth’s volume and 32.5% of earth’s mass.
  • It is the densest layer of the earth with its density ranges between 9.5-14.5g/cm3.
  • It spins independently because it floats in the liquid metal outer core. One cycle of the swing is about seven decades approximately.
  • It 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.

What should one understand about the interior of the earth?

  • It is not possible to know about the earth’s interior by direct observations because of the huge size and the changing nature of its interior composition.
  • It is an almost impossible distance for the humans to reach till the centre of the earth (The earth’s radius is 6,370 km).
  • The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.

Sources of Information about the interior of the earth

Direct Sources:

  1. Rocks from mining area
  2. Volcanic eruptions

Indirect Sources

  1. By analyzing the rate of change of temperature and pressurefrom the surface towards the interior.
  2. Meteors, as they belong to the same type of materials earth is made of.
  3. Gravitation, which is greater near poles and less at the equator.
  4. Gravity anomaly, which is the change in gravity value according to the mass of material, gives us information about the materials in the earth’s interior.
  5. Magnetic sources.
  6. Seismic Waves: the shadow zones of body waves (Primary and secondary waves) give us information about the state of materials in the interior.

What is the new study about?

  • Exactly how the inner core rotates has been a matter of debate between scientists— and the latest research is expected to prove controversial.
  • A new research has analyzed seismic waves from repeating earthquakes over the last six decades.
  • It shows that- the inner core started rotating slightly faster than the rest of the planet in the early 1970s, the study said.
  • But it had been slowing down before coming in sync with Earth’s rotation around 2009.

What made the core spin slower?

  • So far there is little to indicate that what the inner core does has many effects on surface dwellers.
  • The researchers said this rotation timeline roughly lines up with changes in what is called the “length of day”— small variations in the exact time it takes Earth to rotate on its axis.
  • But the researchers said they believed there were physical links between all of Earth’s layers, from the inner core to the surface.


Crack Prelims 2023! Talk to our Rankers

(Click) FREE 1-to-1 on-call Mentorship by IAS-IPS officers | Discuss doubts, strategy, sources, and more

Get an IAS/IPS ranker as your 1: 1 personal mentor for UPSC 2024

Attend Now

Notify of
Inline Feedbacks
View all comments


Join us across Social Media platforms.

💥Mentorship New Batch Launch
💥Mentorship New Batch Launch