Outer Surface of the Earth

The surface of the earth is a complex zone in which three main components of the environment meet, overlap and interact.

  1. Lithosphere is the entire top solid crust of the earth and includes not only the land surface but also the ocean floor.

  2. Hydrosphere is the water surface which includes the oceans, lakes and rivers. It rests on the lithosphere. The Hydrosphere comprises water in all its forms - ice, water and water vapour.

  3. Atmosphere is the blanket of the gaseous air that envelops the earth. It covers both the land surface and the water surface.

Biosphere is the sphere of life which spreads over all the three spheres - lithosphere, hydrosphere and atmosphere.


The solid portion of the earth is called the Lithosphere. It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms. There are two main divisions of the earth’s surface:

  1. Continents - large landmasses
  2. Ocean Basins - water bodies

All the oceans of the world are connected with one another. The level of seawater remains the same everywhere. Elevation of land is measured from the level of the sea, which is taken as zero.

The highest mountain peak Mt. Everest is 8,848 metres above the sea level. The greatest depth of 11,022 metres is recorded at Mariana Trench in the Pacific Ocean.


The earth is called the blue planet. More than 71% of the earth is covered with water and 29% is with land. Hydrosphere consists of water in all its forms. As running water in oceans and rivers and in lakes, ice in glaciers, underground water and the water vapour in atmosphere, all comprise the hydrosphere.

More than 97% of the Earth’s water is found in the oceans and is too salty for human use. A large proportion of the rest of the water is in the form of ice sheets and glaciers or under the ground and a very small percentage is available as fresh water for human use.


The earth is surrounded by a layer of gas called the atmosphere. This thin blanket of air is an integral and important aspect of the planet. It provides us with the air we breathe and protects us from the harmful effects of sun’s rays.

The atmosphere extends up to a height of about 1,600 km. The atmosphere is divided into five layers based on composition, temperature and other properties. These layers starting from earth’s surface are called troposphere, stratosphere, mesosphere, thermosphere and exosphere.


The biosphere is the narrow zone of contact between the land, water and air. It is in this zone that life exists. There are several species of organisms that vary in size from microbes and bacteria to huge mammals. All the living organisms including humans are linked to each other and to the biosphere for survival.