What Is Geology ?

         
               
    The science of Geology is concerned with the Earth and the rocks of which it is composed, the processes by which they were formed during geological time, and the modeling of the Earth's surface in the past and at the present day. The Earth is not a static body but is constantly subject to changes both at its surface and at deeper levels. Surface changes can be observed by engineers and geologists alike; among them erosion is a dominant process which in time destroys coastal cliffs, reduces the height of continents, and transports the material so removed either to the sea or to inland basins of deposition. Changes that originate below the surface are not so easily observed and their nature can only be postulated. Some are the cause of the slow movements of continents across the surface of the globe; others cause the more rapid changes associated with volcanic eruptions and earthquakes. The changes result from energy transactions, of which the most important are listed in Table 1.1 (Smith, 1973):

1.      Solar energy received and re-radiated; responsible for many geological effects
generated within a depth of about 30 m of ground level, especially weathering
and erosion.
2.       Geothermal heat loss from the Earth's interior; responsible for many deep seated movements that affect the elevation and relative position of continents and oceans.
3.       Energy lost by slowing down of Earth's rotation.
4.       Energy released by earthquakes.
The last three items together account for many of the changes that originate below the Earth's surface, and indicate the importance of internal processes in controlling the behavior of the planet. These processes are thought to have operated for millions of years and geologists believe that processes working at present are fundamentally similar to those that operated in the past. The
effects produced by geological processes may appear to be too slow to be significant in engineering, but many of them operate at rates similar to those found in engineering practice. For example, continents drift laterally at a rate of between 1 and 3 cm per year, or at about 10 ~7 cm per second, which is the approximate value for the hydraulic conductivity of good concrete used in dams.
 Geological processes such as those which operate at the present day have, during the very large span of geological time, left their record in the rocks – sometimes clearly, sometimes partly obliterated by later events. The
rocks therefore record events in the long history of the Earth, as illustrated by the remains or marks of living organisms, animals or plants, when preserved; all rocks make their contribution to the record. In one sense geology is Earth-history.
Rocks are made up of small crystalline units known as minerals and a rock can thus be defined as an assemblage of particular minerals, and named accordingly.
 The term rock is used for those materials of many kinds which form the greater part of the relatively thin outer shell, or crust, of the Earth; some are comparatively soft and easily deformed and others are hard and rigid. They
are accessible for observation at the surface and in mines and borings. Three broad rock groups are distinguished, on the basis of their origins rather than their composition or strength:
       
        i.                  Igneous rocks, derived from hot material that originated below the Earth's surface and solidified at or near the surface (e.g. basalt, granite, and their derivatives).

       ii.             Sedimentary rocks, mainly formed from the breakdown products of older rocks, the fragments having been sorted by water or wind and built up into deposits of sediment (e.g. sandstone, shale); some rocks in this group have been formed by chemical deposition (e.g. some lime stones). The remains of organisms such as marine shells or parts of plants that once lived in the waters and on the land where sediment accumulated , can be found as fossils.

  iii.            Metamorphic rocks, derived from earlier igneous or sedimentary rocks, but transformed from their original state by heat or pressure, so as to acquire conspicuous new characteristics (e.g. slate, schist, gneiss). 


Location: Karakoram Hwy, Abbottabad, Pakistan

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