Biosphere/ecosphere is the living mantle or biologically inhabited part of earth (soil, water and air from depth of oceans to tops of mountains) alongwith its abiotic physico-chemical compound. Biosphere extends to some 22.5 km. Life is most abundant at the interfaces of sea, air and earth. Foundation/maintenance of life is based on (i) Flow of energy (ii) Circulation of nutrients or biogeochemical cycles.
Subdivisions of Biosphere:
Biosphere consists three interacting subdivisions, viz., atmosphere, lithosphere and hydrosphere.
(i) Atmosphere:
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It is the transparent gaseous mantle surrounding the earth which extends to several kilometers and in differentiated into troposphere (10- 18 km), stratosphere (18-50 km), mesosphere (50-85 km), thermosphere (85-500 km) and exosphere (500 km to about 1600 km). Troposphere shows lowering of temperature with height (15°C to – 55CC), cloud formation and manifestation of weather conditions. Dust particles are restricted to its lower part.
Stratosphere contains an ozonosphere or ozone layer (for filtering ultraviolet rays) at a height of about 25 km. Ozone (O2) is produced by action of ultraviolet and other high energy radiations on oxygen, resulting in splitting and interaction of oxygen molecules (3O2 -> 2O3). Ionosphere is a region of thermosphere which is protective and radioreflective.
(ii) Lithosphere:
It is outer solid crust of earth. The exposed part or soil supports terrestrial life. It possesses minerals, moisture and organic matter.
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(iii) Hydrosphere:
Hydrosphere is liquid mantle of earth. It is differentiated into fresh water sea water. Both air and water are essential for supporting life.
Closed and Open System:
Earth is an open system of energy. It is continuously receiving solar energy. A fraction of it is trapped by autotrophs. Rest is emitted back as heat waves. Earth is closed system for materials, neither receiving (except for occasional meteorites) nor giving out anyway.
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There is recycling of materials/matter between biotic and abiotic components of biosphere. Energy flows through the biosphere to consumers, consumers to consumers organisms to microbes, as also dissipating as heat.