The earth

The earth is the center of universe around which the Sun, the stars and heavenly bodies revolve. The age of the earth is estimated to be 4.6 billion years. The earth’s central portion is solid in nature and referred to as the inner core. It has a temperature of 4,000°C. This solid core has approximate thickness of 1,370 kilometers and is surrounded by 2,080 kilometers thick outer core which is molten in nature. Further this outer core is surrounded by Mantle having thickness of around 2,900 kilometers. Mantle is surrounded by the earth crust which varies 12 to 60 kilometers in thickness.

The earth is divided into four spheres.

Lithosphere: It is the top crust of earth surface which includes the land surface. It forms 30% of the total surface of earth and constitutes the upper land surface having sand and soil.

Hydrosphere: It is surface of earth having water i.e. Oceans, Lakes, Rivers etc.

Atmosphere: It is the envelope of air surrounding the land and water surface. The atmosphere is composed of various gases and water vapors. It is an insulating blanket protecting the earth surface. It has further four layers.

i. Troposphere

ii. Stratosphere

iii. Mesosphere

iv. Ionosphere

Biosphere: It is that sphere of earth which spreads over all the above three spheres. It is generally refers to as the Ecosystem.