The biosphere is the sphere of earth where living organisms exist penetrating the lithosphere, the hydrosphere and the atmosphere. This zone of life is vast and covers most life forms from microbes to huge mammals. This zone supports several varieties of        organisms, both plants and animals. There are about 10,00,000  varieties of animals and 3,00,000 varieties of plants. Some of them are so minute that they can be viewed only with the help of a microscope while others are quite big and huge. Some of them      live under the surface of the earth while others live deep under water and still others roam about on the earth or in the air.

Man and Biosphere
    Human beings–an essential part of the biosphere-have disturbed the natural balance between the different elements of the biosphere by their activities. This has led to serious environmental problems-threatening the very existence of many pieces.
    Man has excavated mines and extracted coal, petroleum and natural gas from the earth. The burning of coal oil and natural gas, and cutting down of trees and reckless in industrial practices are altering the composition of the gases in the atmosphere and         polluting it. Increase in the level of carbon dioxide and some hanuful gases has led to global warming, climate change, depletion of the ozone layer, changes in sea level, melting of ice caps and high levels of pollution. Our earth is the only planet with a               congenial environment for life.

                                                                 Key Words

LITHOSPHERE :      The solid domain of the earth forming the land which supports animals, plants and humans.
HYDROSPHERE :    The water that fills the depressions of the earth's surface comprising of water bodies like the oceans, seas, rivers and ponds.
ATMOSPHERE :       The vast expanse of air that surrounds the earth.
BIOSPHERE :           The zone which contains all forms of life penetrating the lithosphere, hydrosphere and the atmosphere.
ISTHMUS :                A narrow stretch of land joining two larger landmasses.
TROPOSPHERE :    The lowest layer of the atmosphere near the earth's surface where all the weather phenomena takes place.
STRATOSPHERE :  The layer above the troposphere where the ozone layer is found.
MESOSPHERE :    The third layer of the atmosphere where the temperature drops as low as –110°C.
IONOSPHERE :    The fourth layer of the atmosphere that contains electrically charged particles called ions.
EXOSPHERE :    The last layer of the atmosphere which finally merges into space.