We are familiar with the three spheres of the planet earth; lithosphere, atmosphere and hydrosphere. But little attention has been paid to the fourth sphere surrounding the earth. It is the biosphere which includes all living components comprising plants, animals and all the micro organisms inhabiting the earth.

All these living components of the biosphere are engaged in the interactions with their surroundings. Because of the presence of living organisms the biosphere has rightly been called the life layer of the planet earth.

Most of the organisms live on the lithosphere or hydrosphere as well as in the atmosphere. However, there are many organisms that move freely from one realm to another. As a matter of fact, life on the earth is present everywhere, from the poles to the equator, from the bottom of the sea to the higher reaches of the atmosphere.

The living organisms are present even in the freezing waters or in the dry vallies; even underground water below the earth surface is not without living organisms. This sphere of life and organic activity extends from the bottom of the oceans to about a few kilometers (8 to 10 km.) in the atmosphere.


The term ‘biosphere’ was used for the first time by Edward Suess, the Austrian geologist in 1857. The concept was later on modified by Vernadsky, the Russian mineralogist in 1926. Some of the definitions of biosphere given by eminent scientists are being given as under:

Odum, E.P:

“Biosphere is a widely used term for all of the earth’s ecosystems functioning together on the global scale.” According to Odum, biosphere is that portion of the earth in which ecosystem can operate. Remember that biosphere merges freely into the lithosphere, hydrosphere and atmosphere.

Hutchinson :


“Biosphere is that part of the earth where life exists. Thus, the parts of the hydrosphere, lithosphere, and atmosphere where life is found may be termed as biosphere or ecosphere.”


“Ecosphere is that environment in which living beings exist with air, water and land, and interact with their environment. Biosphere is a biochemical system which stores and uses the solar energy”.



“Biosphere encompasses the entire near-surface zone of the earth favourable to life in one form or another.”

Keeping in view all the above definitions, the biosphere may be considered a thin layer of rocks, soil, water and air surrounding the planet earth in which all the living organisms live and interact with their physical environment.

The biosphere should be assumed to be a vast ecosystem where abiotic and biotic components are subject to interaction between them, producing structural and functional changes in it (the ecosystem).

The earth’s biosphere comprises three environmental divisions, namely, the oceans, the land and the atmosphere. It has been proved that the environment has been respon­sible to bring the biosphere to its present state.


But there is little doubt that the biosphere has in turn also modified the environment to the large extent. It is to be noted that the evolution of the photosynthesis was to be credited for the gradual changes in the environmental con­dition. Photosynthesis being a complicated pro­cess will be discussed separately.