Geology

Physical Geology

Physical geology includes such disciplines as: geophysics (applies principles of physics to the study of the earth); geochemistry (the study of the chemical characteristics of minerals and rocks); mineralogy and petrology (the study of the origin, properties, structure, and classification of minerals and rocks, respectively); hydrogeology (the study of the origin, occurrence, and movement of water masses); structural geology (the study of the deformational history of rocks and regions and of the forces responsible); geomorphology (the study of the origin and modification of land-forms); volcanology (the study of volcanoes and magma formation processes); sedimentology (the study of sedimentary rocks and the processes by which they were formed); and engineering geology (the study of the interactions of the earth's crust with human-made structures such as tunnels and mines).

Some areas of specialization for professional geologists related to physical geology include exploration and extraction of natural resources (mineral deposits, coal, oil, etc.), prediction and evaluation of geological hazards (landslides, earthquakes, volcanic eruptions, or meteoritic impacts), evaluation of the stability of construction sites, the search for supplies of clean water, and analysis of environmental problems such as soil and coastal erosion.

Historical Geology

A consubstantial part of geology is the study of how Earth's materials and continents, surface environments, processes, and organisms have changed over geological time. Processes, fossils, and geological events are recorded in rocks. Thus the main objective of historical geology is the analysis of the geological record in order to reconstitute and understand the earth's history. Historical geology is based on paleontology (the study of life in the past from the fossil record, including evolutionary relationships, and its applications in environmental reconstructions and in the relative dating of rocks); stratigraphy (the study of stratified rocks in terms of mode of origin, original succession, relative dating, and geologic history), and paleogeography (the reconstruction of the ancient geography of the earth's surface). Other important disciplines closely related to historical geology are: paleoclimatology (the application of geological science to determine past climatic conditions) and paleoceanography (the reconstruction of the history of the oceans, with regard to circulation, chemistry, or patterns of sedimentation).

When geologists come to interpret the earth's history, they rely on two complementary types of dating of rocks: relative dating and absolute dating. Relative dating places historical events in their correct temporal order, and absolute dating provides a numerical age for a rock and establishes how many years ago a geological event took place.

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