18) Write brief notes on atmosphere, hydrosphere and lithosphere.
The global environment consists of atmosphere, hydrosphere and lithosphere in which the life-sustaining resources of the earth are contained. The atmosphere , which is a mixture of various gases (mainly nitrogen, oxygen, carbon dioxide and water vapour) extending outward from the surface of the earth, evolved from the elements of the earth that were gasified during its formation. The hydrosphere consists of oceans, lakes and streams and shallow ground water bodies. The lithosphere , on the other hand, is the soil mantle that wraps the core of the earth. (The biosphere, a thin layer that encapsulates (enclose in) the earth, is made up of atmosphere and lithosphere adjacent to the surface of the earth, together with hydrosphere It is within the biosphere that all the life-forms of earth live. Life-sustaining materials in solid, liquid and gaseous forms are cycled through biosphere, giving sustenance to all the living organisms. Life-sustaining resources, air, water and food, are withdrawn from the biosphere.