The earth is a very complex place. It has been divided into four sphere, to enable us to understand it separately and how each sphere interacts with each other.
What are the four major domains of the earth?
The four major domains are divided as :
- Lithosphere – Lithosphere is the solid shell of the earth and is divided into a crust and mantle.
- Atmosphere – Atmosphere is a layer of gases surrounding a planet, held in place by the gravity of the body.
- Hydrosphere – Hydrosphere is the combined mass of water present on the surface or under the surface, on a planet.
- Biosphere – Biosphere also known as the ecosphere, is all the connected ecosystems on a planet.
What is lithosphere?
The word lithosphere is derived from two Greek words, Lithos, meaning rocky and Sphere meaning rigid. Every rocky planet has a lithosphere. The lithosphere is the outermost shell of the planet earth, which consists of the crust and the upper mantle. The upper mantle behaves elastically over thousands of years.
The earth’s lithosphere is divided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process, is called the pedosphere. The shifting of tectonic plates over millions of years is responsible for the changing earth’s surface.
What are types of lithosphere?
The earth’s lithosphere is of two types : oceanic and continental lithosphere.
1. Oceanic lithosphere
- It consists mainly of mafic (rich in magnesium and iron) crust and ultramafic (over 90% mafic) mantle and is denser than continental lithosphere.
- It thickens as it ages and moves away from the mid ocean ridge.
2. Continental lithosphere
- It is also called the continental crust. It is the layer of igneous, sedimentary rock that forms continents and the continental shelves.
- This layer consists mostly of granitic rock.
- The oldest oceanic lithosphere is about 170 million years old compared to parts of the continental lithosphere which are billions of years old.
What is the continental drift?
Under the lithosphere layer, is a molten layer, which is in constant motion. This layer is known as asthenosphere. The lithosphere layers, both the crust and the mantle, are constantly being shaken or disturbed by the movement in the asthenosphere layer. These movements over a period of time, start changing the position of the land masses referred to as continents. This phenomenon, which takes thousands of years is known as continental drift and changes the surface topography of the planet.
Major plates of the lithosphere
- African Plate
- Antarctic Plate
- Eurasian Plate
- Indo-Australian Plate
- North American Plate
- Pacific Plate
- South-American Plate