Geography Study Notes on Earth

We all know that earth is the only planet among the eight planets where life is possible. Can you answer that why life is possible on the earth? The answer is simple that earth possesses a balanced atmosphere and a very important element that is essential for all the organisms; water. Life on earth exists due to the presence of water and appropriate distance between the sun and the earth i.e., the earth is neither too far from the sun nor too close which avoids making it either excessively cold or hot for a life form to exist.

70% of the earth is covered with water and it appears blue from the space that is why it is also called the blue planet.

Movement of the Earth:

Movement of the earth are of two types:

Rotation:

Rotation is the spinning of the earth on its own axis. Earth completes one rotation in 23 hours 56 minutes 4.09 seconds. Earth moves in rotation from west to east. Rotation of earth causes day and night. The part of the earth that receives sunlight, there is day and where sunlight does not reach, there is night.

Revolution:

When the earth moves around the sun in an orbit is called a revolution. The earth completes one orbit in about 365 days, 48 minutes and 45.68 seconds. Generally, a year is of a total of 365 days and the remaining 48 minutes and 45.68 seconds of each year make 24 hours in four years. These extra 24 hours add up and make an extra day. Eventually, the fourth year has 366 days and is known as a leap year. Hence in the leap year, February is of 29 days.

Structure of Earth:

Earth is made up of three layers:

1. Crust:

The crust is the outermost layer of the earth's surface. The crust is made up of metamorphic, igneous and sedimentary rocks. Earth crust is of two types i.e., continental crust and oceanic crust. The temperature of the earth increases with increase in depth. At every 32 meters the temperature of the earth increases by 1^o.

2. Mantle: 

It is the second layer of the earth's surface. The mantle consists of 2 layers i.e., upper mantle and lower mantle. It is 2900 kilometres thick and consists of 83% of the earth's volume. The upper mantle consists of 100 to 200 kilometres below the surface is called asthenosphere. The lower mantle is situated just below the upper mantle. The lower mantle extends from 670 to 2700 kilometres. This layer is hotter and denser making it appropriate for the formation of minerals.

3. Core:

The core is the innermost layer of the earth’s interior. This layer is rich in iron and nickel. The outermost layer of the core is in the form of liquid whereas the innermost core is in the form of solid.

Domains of the earth:

1. Lithosphere:

The portion of the earth where we live is known as the lithosphere. It is the solid portion of the earth surface which consists of a thick layer of the soil with nutrients and rocks.

2. Atmosphere:

The atmosphere is a thick blanket of air which is constituted with a number of gases. The various gases of the atmosphere are oxygen, nitrogen, carbon dioxide, and others.

3. Hydrosphere:

The hydrosphere is the total amount of water which is present on the earth in solid, liquid and gas form. The solid part of the hydrosphere is in the form of ice (iceberg, glaciers, and icecaps), liquid part of the hydrosphere is present in the form of river, sea, ponds, lakes, groundwater, etc. and gaseous part of the hydrosphere is present in the form of water vapours.

4. Biosphere:

The biosphere is the global ecological system where we find all the four zones existing together. This zone is the life support system for all the life forms from a tiny worm to the giant elephant.

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