The Earth and The Envinonment:Concepts covered in this module are:PhysicalComponenets of the Earthare: 1 ATMOSPHERE.2. HYDROSPHERE and 3.GEOLOGICAL LAYERS. Envinonment and its factors1. CLIMATE.2.MICROCLIMATE and3. HABITAT and NICHE.INTRODUCATION:The study of the relationship between living organisms and their environment is called Ecology.The word "ecology " was derived from the greek words "oikos" meaning "habitation" or "home" and logos meaning "study" or "discourse".Ecology has two main divisions -- AUTECOLOGY and SYNECOLOGY.Autecology is the study of interrelationships between individual organisms of the same species or population and their environment.Synecology is the study of the interrelationships between different species of organisms and their environment.The Earth is oblate spheroid in shape with an average diameter of approximately 12,742 km.The earth consists of - ATMOSPHERE, HYDROSPHERE and GEOLOGICAL LAYERS.These three parts consists the physical components of the earth.ATMOSPHERE:The gaseous envelope surrounding the earth consitutes the atmosphene. Four distinct layers are recognized in the atmosphere.TROPOSPHERE:It is the lowest layer of the atmosphere close to the surface of the earth. It extends to a height of 8-10 km above the earth's surface at the poles and 16 -18 km at the equator.The pressure and temperature of the air decreases gradually as the height increases from the earth's surface.It's the densest layer occupying 75% of the mass of atmosphere. Temperature at troposphere decreases to -57 degree celcius.Troposphere extends uptotropopause, where stratosphere begins.STRATOSPHERE:It occurs beyond the tropopause, extending to about 50 to 55 km above the earth's surface.It contains ozone layer which absorbs ultraviolet radiation and there by protects the organisms on the earth from the harmful effects of radiation.Temperature increases with attitude.The end of stratosphere is called stratopause.IONOSPHERE:The part of the atmosphere extending from about 50-500 kilometers.

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