concentrically divided into a number of spheres viz.,
Atmosphere ; (2) Hydrosphere and (3) Lithosphere .
The outermost sphere is Atmosphere which consists of several gases and vapours and
envelopes the earth. Atmosphere is essentially a mixture of N2 and O2 with smaller
quantities of vapour, CO2 etc… Geologically atmosphere is important as the medium of
climate and weather. Hydrosphere includes the natural waters of the earth ie., oceans,
seas, lakes, rivers, streams and underground water. Lithosphere is the outer part of the
earth’s crust consisting of rocks and minerals.
The geological processes include Denudation, Deposition, Earth movements, Igneous
activity and metamorphism.
Denudation: The sum of the processes which result in the general lowering of the land
surfaces or when erosion takes place, fresh country rock surfaces will be exposed and this
process is called DENUDATION. Denudation consists of weathering, transportation and
Weathering is the process by which rocks are broken down and decomposed by the action of
external agencies such as wind, rain, temperature changes. Weathering is the initial stage in
the process of denudation.
Transportation is the main agency by which materials are moved by means of Gravity,
running water ( rivers, streams ); Ice ( glaciers ); Wind etc..
Mechanical disintegration or chemical decomposition of rocks and their
subsequent displacement is called as erosion or erosion is the destructive process due to
the effect of the transporting agents. The chief agents of erosion are running water, wind
Deposition : The material is transported mechanically and deposit (eg: sand ).
Earth movements include the uplift and depressions of land areas & sea floors.
Igneous activity includes emission of lavas, gases, other volcanic products etc
Metamorphism: The process by which changes are brought about in rocks within the
earth’s crust by the agencies of Heat, Pressure and Chemical fluids.
: heat alone acts
: involves stress to break up the rocks
Regional/Dynamothermal metamorphism: Both heat & pressure involves
Retrograde metamorphism : produces lower grade metamorphic rocks
: chemical adjustment in newly solidified igneous rocks,
brought about by a decrease in temperature .