Context: New research has suggested that the Earth's inner core may have undergone a significant transformation in its shape over the past two decades.
Relevance of the Topic:Prelims: Key facts about Internal Structure of Earth: Crust, Mantle and Core.
Internal Structure of Earth: Crust, Mantle and Core
- The structure of Earth is divided into four major components: Crust, Mantle, Outer core, inner core.
- Each layer has a unique chemical composition, physical state, and can impact life on Earth's surface.
LAYERS OF EARTH
1. CRUST
- It is the outermost solid part of Earth and is brittle in nature.
- Average density of outer and lower crust is 2.7 and 3.0, respectively.
- Oceanic crust is thinner (5 Km) as compared to continental crust (30 Km)
- Continental crust is thicker in areas of major mountain systems (it is as much as 70 km thick in the Himalayan region).
MANTLE:
- The portion of interior beyond the crust is called mantle. It extends from Moho’s discontinuity to a depth of 2,900 km.
- The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km.
- The upper portion of the mantle (lower part of Lithosphere) is called Asthenosphere which is partially molten in condition whereby molten magma is in motion (it extends up to 400 km).
- The lower mantle extends beyond the asthenosphere. It is in solid state.
- Previously mantle was divided into two zones:
- Upper Mantle from Moho’s discontinuity to 1000 km depth
- Lower Mantle from 1000 to 2900 km depth.
On the basis of discovery by the International Union of Geodesy and Geophysics, the mantle is now divided into three zones.
- Zone 1: Moho’s discontinuity to 200 km depth
- Zone 2: 200 – 700 km depth
- Zone 3: 700 – 2900 km depth
3. CORE:
- The core-mantle boundary is located at the depth of 2,900 km.
- The outer core is in liquid state while the inner core is in solid state.
- Composition of Core: Core is made up of very heavy material mostly constituted by Nickel and Iron. It is sometimes referred to as the NiFe layer.
Significance of the Core:
- Contains information regarding earliest history of accretion of planet
- Earth's core plays a vital role in sustaining life on our planet and generates a magnetic field that shields us from the Sun's harmful radiation.
- The inner core rotates independently of the liquid outer core and the rest of the planet, creating a dynamic motion that is essential for maintaining Earth's magnetic field.
- Without dynamic motion, our planet would be unable to support life, and would likely become a barren, Mars-like landscape.
Findings of the New Study:
- Research paper – “Annual Scale variability in both the rotation rate and near surface of Earth’s inner core”.
- It is published in the scientific journal Nature Geoscience.
- Highlights of the Study:
- The inner core of the Earth may have noticeably changed shape over the past few decades.
- Contrary to the long-held belief that the inner core is a perfect sphere, a team of scientists has proposed that its edges may have deformed by as much as 100 meters or more in certain areas. The change could have happened at the inner core’s outer boundary.
- Previous studies have found that the inner core spins slightly faster than the outer layers, scientists believe that the pace of rotation is slowing down.
- The researchers suggest that the liquid flow of the outer core, combined with the uneven gravitational field, may be causing the inner core to deform.
How was the study conducted?
- Scientists study the behaviour of seismic waves to understand the earth's interior. They can infer the types of materials, density, and elasticity of rocks by analysing the speed and direction of seismic waves.
- This time scientists have examined seismic wave patterns from earthquakes that occurred repeatedly in the same location (South sandwich island, Southern Atlantic Ocean) between 1991 and 2023.
- By comparing these patterns over time, the researchers aimed to understand how the inner core has changed.
Significance of the research:
- Findings are not that significant from the perspective of daily lives.
- However, significance lies for the scientific community, so as to enable them to make more informed estimates of some important material properties, and to understand the earth’s interior and process therein.