Q1. How do the meterorites help scientists to know about the interior of the earth ? Ans:- Keeping in mind the theories of the origin of the earth, scientists study meterorits which fall on the surface of the earth. The earth is said to be constituted of the same materials as the meteorites.
Q2. What is the Lithosphere ? Ans:- The solid portion of the earth on which we live is called the Lithosphere.
Q3. What is Atmosphere? Ans :- The gaseous layer that surround the earth, is the Atmosphere.
Q4. What is Hydorsphere? Ans:- The water, ice, oceans, water vapour and all other forms is called Hydrosphere.
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 almost impossible for the humans to reach to the centre of the earth. (The earth’s radius is 6,378 km).
- Through mining and drilling operations, we have been able to observe the earth’s interior directly but only up to a depth of few kilometers.
- The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.
- Still, through some direct and indirect sources, the scientists have a fair idea about how the earth’s interior look like.
The 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 Magnesium.
- The upper continental layer is lighter and consists of Silicates and Aluminium - SIAL (Sometimes SIAL is used to refer Lithosphere, which is the region comprising the crust and uppermost solid mantle, also).
- The lower oceanic crust is dense and consists of Silicates and Magnesium – SIMA.
- The outer crust has valuable soil and provides us with most of the minerals.
- The crust is made up of many kinds of rocks and the density of rocks increases with an increase in depth.
The Mantle - The portion of the interior beyond the crust is called the mantle.
- The discontinuity between the crust and mantle is called as the Mohorovicic 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 uppermost solid part of the mantle and the entire crust constitute the Lithosphere.
- The asthenosphere (in between 80-200km) is a 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 portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.
The 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.
- The core constitutes nearly 15% of the earth’s volume and 32.5% of the 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 the solid state and the outer core is in the liquid state (or semi-liquid).
- The discontinuity between the mantle and the core is called as the Guttenberg’s Discontinuity.
- Barysphere (which means heavy metallic rock) is sometimes used to refer the core of the earth or sometimes the whole interior.
- The outer core is in molten state, whereas the inner core is firm and solid due to high pressure.
- The presence of heavy metals and iron may be responsible for the earth’s magnetism.