Environmental Segments

The environment consists of four segments – atmosphere, hydrosphere, lithosphere and biosphere.

1. Atmosphere: The three layers of air that envelop the earth are known as the atmosphere. It is the protective blanket of gases surrounding the earth, which sustains life on earth and saves it from the hostile environment of outer space. It absorbs harmful radiation from the outer space and a major portion of the electromagnetic radiation from the sun. The atmosphere is essential for all living organisms. The major components of the atmosphere are nitrogen (78.09 per cent) and oxygen (20.94 per cent), while the minor components are argon, carbon dioxide and some trace gases. Based on temperature, the earth’s atmosphere can be divided into four major zones, namely, troposphere, stratosphere, mesosphere and thermosphere.
2. Hydrosphere: The aqueous envelope of the earth, including the oceans, all lakes, streams, rivers, subsurface waters, water vapour in the atmosphere and water in the form of ice, constitutes the hydrosphere. About 97 per cent of the earth’s water supply is in the oceans, where the high salt content does not permit its use for human consumption. About 2 per cent of the water resources is locked in the polar ice caps and glaciers, while 1 per cent is available as freshwater (surface water such as rivers, lakes and streams, and groundwater) for human consumption and other uses.
3. Lithosphere: The soil component of the earth is called lithosphere. This is the outer mantle of the solid earth, consisting of minerals occurring in the earth’s crust and the soil.
4. Biosphere: This denotes the realm of living organisms and their interactions with the environment, namely the atmosphere, hydrosphere and lithosphere. Both the biosphere and environment are influenced considerably by each other.