Interior of the Earth
Source of information
- Direct sources - Deep ocean drilling & Volcanoes
- Indirect sources - Density studies, Temperature & Pressure, Seismic studies, Meteorites Gravitational forces and Magnetic survey
Volcanoes - Volcanoes are major source of direct information. They tell us about the composition and characteristics of the materials found inside the Earth.
Temperature - Temperature goes on increasing with the increase in depth inside the Earth. On average, there is a rise of 1 degree centigrade temperature for every 32m of depth.
Density - Density too increases with the increase in depth.
- Surface density - 2.7 - 3 g/cubic cm
- Core density - 13 g/cubic cm
- Average density of the Earth - 5.5 g/cubic cm
Pressure - Just like temperature and density, pressure too increases with the increase in depth.
Gravitational force - It is not same at all places on the surface of the Earth. It depends on many factors such as latitude, mass of the material, uneven distribution of mass of material within the Earth, etc. Such differences in gravity is known as Gravity anomaly. It gives us information about the distribution of mass of material inside the Earth.
Magnetic survey - The Earth also acts like a huge magnet. The magnetic survey provides information about the distribution of magnetic material inside the Earth.
Meteorites - They too have originated during the formation of Solar System. It is therefore, very much in order to believe that both meteorites and Earth are made up of similar materials.
Seismic waves - Earthquakes are caused by the movements in the interior of the Earth. Earthquake waves are basically of two types n- body waves and surface waves. The velocity of these waves changes as they travel through materials of different densities. There direction also changes (reflect/refract) as they move through materials of different densities.
Structure of Earth's interior
Chemical division - Crust, Mantle & Core
Crust 🠚 Silicon
- Continental curst - SiAl (thick) 🠚 Light colour, less dense (2.7), older, mostly Aluminum & Sodium are present
- Oceanic crust - SiMa (thin) 🠚 Darker, more dense (3.0), younger, mostly Magnesium & Calcium are present
Mantle 🠚 Magnesium (by volume - 83% & by mass - 68%)
Core 🠚 Nickel & Iron (outer core - liquid & inner core - solid)
Crust - It is the uppermost layer of the Earth which is lighter in density and mainly made up of Silica. It is made up of continental crust and Oceanic crust.
Mantle - It is a solid layer divided into upper mantle and Lower mantle with increase in density towards the lower layer. The composition would be increase in Magnesium content with depth. It consists of 83% of total volume of the Earth and 68% of Mass.
Core - It is the innermost layer of the Earth. It is also called NiFe layer due to the presence of high percentage of Nickel and Iron with density reaching upto 13g/cubic cm. Core is divided into outer core and inner core with outer being liquid due to melting of rocks and inner core is solid as the high pressure increases the melting point of rocks.
Physical division of the Earth - Lithosphere, Asthenosphere, Mesosphere & Barysphere
Lithosphere - very hard rocky layer, includes crust & upper part of the upper mantle
Asthenosphere - bit soft, semi-fluid & semi-solid (i.e., plastic in nature), also known as low velocity zone, present in upper mantle
Mesosphere - rest of mantle
Barysphere - core
Lithosphere - It is a solid layer made up of crust and upper mantle. Its thickness is upto 100 KM.
Asthenosphere - It is plastic in nature with low viscosity with depth between 100 to 400 KM. It is called as Low velocity zone because of slowing down of the Earthquake waves in this zone. This is also a source of magma which reaches to the surface through volcanoes.
Mesosphere - The rest of the mantle is called as mesosphere.
Barysphere - It includes both outer and inner core.
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| Source: NCERT |
Discontinuity - It is a transition zone in the Earth's interior between different layers of differing physical and chemical characteristics. There are 5 discontinuities present in Earth's layer.
- Conrad discontinuity- within Earth's crust
- Moho/Mohorovic discontinuity - Between crust and Upper mantle
- Repetti discontinuity - Between Upper and Lower mantle
- Gutenberg discontinuity- Between Mantle and Outer core
- Lehmann discontinuity- Between Outer and Inner core
Previous Article - Geomorphology: An introduction
Next Article - Rocks & Types of Rocks
Notes on other subjects
Optional Notes
Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own.
Hope! It will help you to achieve your dream of getting selected in Civil Services Examination 👍
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