The earth is the only planet where conditions are suitable for the existence of life. This is because of the presence of the land, water and air on the earth.
The uppermost solid part of the earth is called lithosphere. It is made up of rocks and soils. Sometimes it is also called the crust. The greater part of the surface is water and the remaining part of the earth surface is in the form of land masses. The height of any point on the lithosphere is measured with reference to the sea level.
The large continuous masses of land above the earth's surface are called the continents. There are seven continents.
A conical mass of land rising to much greater heights than the surrounding areas is called a mountain. A plateau is a large area of fairly level land raising much above the surrounding area. A plain is a low-lying area with a flat surface.
The water mass of the earth, including oceans, oceans, seas, rivets, lakes, underground water, ice-sheets and water vapors in the atmosphere is called hydrosphere. The major part of the hydrosphere consists of the four oceans. Water masses smaller than oceans are called seas.
All around our earth, there is a cover of air. This cover of air is known as atmosphere. This atmospheric cover extends to a height of about 1600 kilometers from the earth surface.