Geology (from Greek γη- (ge-,"the earth") and λογος (logos, "word", "reason")) is the science and study of the earth , its make-up, structure, physicalproperties, history, and the processes that shape it.
Geology has helped established that the earth is about 4.5 billion years old, and that tectonic plates move over a viscous mantle to form the earth'scrust. Geology helps us locate and manage the earth's naturalresources , such as oil .
Geology is also sometimes used about similar studies of other bodies of the solar system. However, specialised termssuch as selenology (studies of the Moon), areology (of Mars), etc., are also in use.
The word was first used by Jean-André de Luc (1727 - 1817)in the year 1778 and introduced by Horace-Bénédict de Saussure (1740 - 1799) in the year 1779 as a fixed term. [An older meaning of the word is first used by Richard de Bury (1286 - 1345). He used it to distinguish between earthly and theologicaljurisprudence.]
Georg Agricola (1494-1555) wrote the first systematic treatise about mining and smelting works, De remetallica libri XII, with an appendix Buch von den Lebewesen unter Tage (book of the creatures beneath the earth).He covered subjects like wind energy , hydrodynamic power , melting cookers,transport of ores , extraction of soda , sulfur and alum , and administrative issues. The book waspublished in 1556 .
James Hutton is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh . In his paper, he explainedhis theory that the Earth must be much older than had previously been supposed, in order to allow enough time for mountains to be eroded , and for the sediment to formnew rocks at the bottom of the sea, which were then raised up to dry land.
Followers of Hutton were known as plutonists because they believed that some rocks were formed by vulcanism which is the deposition of lava from volcanoes, as opposed to the neptunists, who believed thatall rocks had settled out of a large ocean whose level gradually dropped over time.
William Smith (1769-1839) drew some of thefirst geological maps and began the process of ordering rock strata (layers)by examining the fossils contained in them.
Sir Charles Lyell first published his famous book,Principles of Geology, in 1830 and continued to publish new revisions until he diedin 1875 . He successfully promoted the doctrine of uniformitarianism . This theory states that slow geological processes occurred throughout the earth'shistory, and are still occurring today. In contrast, catastrophism is thetheory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. (Hutton believed inuniformitarianism, but the idea was not widely accepted at the time.)
See also: Timeline of geology
There are many different fields within the discipline of Geology, and it would be hard to list all of them. Some include,however: geochemistry , hydrogeology (or geohydrology ), petroleum geology , economic geology , soil science , climatology , biogeology , geodetics and geophysics .
Subdisciplines within geology proper include structuralgeology , sedimentology and stratigraphy , mineralogy (study of minerals), petrology (study of rocks), geomorphology (study of landforms), seismology (also afield in geophysics ) and volcanology (the study of volcanoes).
There is also engineering geology , which supports civil engineering , especially geotechnical engineering , and geologicalengineering . The difference between geological engineering and engineering geology is real: geological engineers are licensedas engineers, engineering geologists are licensed as geologists.
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