Our home planet “The Earth” is a member of the solar system. Also known as the ‘Blue Planet’, it is the only heavenly body of revolution that has a delicate balance of physico-chemical conditions, which support sustenance of life that is unique and special.
Geology is a natural scientific discipline and is a term derived from the summation of two ‘Greek’ words such as ‘Ge or Geo’ meaning the earth and ‘Logos’ meaning science or discourse. It pertains to the study of the earth as a whole or part thereof. In a broader sense, geology could be reframed as ‘Earth Science’ which considers the whole earth as closed system, which is ever dynamic and a mosaic of four interactive
parts that are ever changeable both among and within them. These four parts are called four reservoirs of materials of the earth (Fig.1.1) which also represent the four open systems such as
(i) THE ATMOSPHERE which surrounds the earth’s surface as a continuous canopy (layer) composed of a gaseous mixture of nitrogen (N), oxygen (O), hydrogen (H), carbon Sun Long-wave radiation Short-wave radiation Geosphere Long-wave radiation Atmosphere Biosphere Hydrosphere Long-wave radiation Long-wave radiation
dioxide (CO₂) and water vapour (H₂O1).
(ii) THE HYDROSPHERE which forms the storehouse of earth’s total water regime comprising the oceanic and sea water, stream (river) water, lake water, surface run-offs, frozen water in form of snow and ice, and underground water
(iii) THE GEOSPHERE, which is the solid earth composed of soils, regolith (loosely cemented rock particles), solid rocks, layers of rock-metal association and metallic alloys (Fe-Ni), as is observed and interpreted from the top towards the centre of the earth.
(iv) THE BIOSPHERE which forms the earth’s organic world comprises of the living beings and the undecomposed organic matters. This sphere persists through all the aforesaid spheres. Biosphere is considered as an informal sphere as against the former three, which are the formal ones.
Geology, as a word was first used by the Swiss natural scientist named Jean Andre Deluc in 1778 and was later introduced as a formal and fixed scientific term by Horace – Benedict de Saussure.
The term ‘Geology’ or the Earth Science’ in a nutshell pertains to the scientific study of the earth, its composition, structure, physico-chemical attributes, developmental history and above all the natural processes, which shape it. The earth is essentially a closed system or very close to it in which the energy reaches the earth from the sun and eventually returns to the space as long wave radiations (Fig. 1.1).
SCOPE OF GEOLOGY
The scope of geology covers a rather wide spectrum in conjunction with other fundamental and applied scientific disciplines such as Physics, Chemistry, Botany, Zoology, Geography and Planetary and Atmospheric sciences. With time, new frontiers of advanced subjects like Geophysics, Geochemistry, Geobotany, Bio-geology, Environmental geology, Astro-geology have also come up. Even
with a subject like political science, it has a link forming an interdisciplinary subject called ‘Geo-politics’. In anthropological and archaeological disciplines, geology enters as a subject to deal with the socio-physical aspects of human race and the stone and metallic implements used during different lithic (Paleolithic, Mesolithic, Neolithic) and later ages.
This subject also enters to the remote discipline of ancient history. An important sub-discipline of geology is ‘Economic Geology’ an applied branch which is directly linked with the study of the vast kingdom of metallic and nonmetallic economic minerals including the industrial minerals and rocks. Economic geology plays a vital role in boosting the developmental growth and industrial strength of the nations and their people. –
SUBDIVISIONS (BRANCHES) OF GEOLOGY
The domain of geology abounding its widened scope is further divisible into a seemingly great number of subdivisions termed as the branches for the sake and convenience of systematic study. The main and allied branches of geology may be named as follows:
The cardinal themes of the main branches are briefed as follows:
General Geology: It is the formal branch of geology that deals with the broad features / aspects of the earth in particular and the other members of solar family with the Sun as the kingpin and sole controller. It also deals with certain principal aspects of the cosmos the ordered universe. The features of the earth include its origin, age, constitution, internal structure and the depth zones of the marine (oceanic) realms.
Physical Geology: It serves as a tool to understand the physical process, which moulds the earth surface. The terms, synonymous with this branch, are ‘geomorphology’ and ‘dynamic geology’. This branch deals with (i) the geometry (ii) origin and developmental history of landform features of mountains, plateaus, valleys, rivers, lakes, glaciers, deserts, oceans and ground water (iii) geological work of the exogenetic (external) geological agents mentioned above, in constantly transforming the features of the earth’s surface and (iv) aspects of natural geologic phenomena such as denudation, weathering, erosion, mass wasting, landsides, soil creep, avalanches and soil erosion.
Geotectonics: This branch deals with the major and very large sized structures of the earth’s lithosphere (the crust and its lower part) and their changes produced by crustal deformation brought about by the interplay of the earth’s endogenetic (internal) forces. It describes and explains the geometry and mode of formation of the mega (very large scale) crustal features and their causative processes. These features are lofty fold mountains, block mountains, rift valleys, mid-oceanic ridges, geosynclines, and island arcs etc. It also deals with the global concepts of isostasy, eustasy (sea level changes), continental drift, convection cells, seismicity, ocean-floor-spreading and the plate-tectonics. In a simple sense, this sub-discipline deals with the movements of various crustal parts and the