What is Geology?
{{distinguish|Geodesy|Geometry}} [[File:Ordovicium-Silurian.jpg|thumb|300px|Photo of the [[Ordovician]]–[[Silurian]] boundary. Due to the folding of the Caledonian [[mountain]] range, the layers have been inverted (turned right over). This left the earlier Ordovician [[limestone]] sitting on top of the later Silurian brownish [[mudstone]].]] '''Geology''' is the study of the nonliving things that the [[Earth]] is made of.<ref>Neuendorf, K. K. (2005). Glossary of geology. Springer Science & Business Media.</ref><ref>Oldroyd, D. R. (1996). Thinking about the Earth: A history of ideas in geology. Harvard University Press.</ref> Geology is the study of [[Rock (geology)|rocks]] in the [[Earth's crust]]. People who study geology are called '''geologists'''.<ref>Raab, T., & Frodeman, R. (2002). What is it like to be a geologist? A phenomenology of geology and its epistemological implications. Philosophy & Geography, 5(1), 69-81.</ref> Some geologists study [[mineral]]s (mineralogist) and the useful substances the rocks contain such as [[ore]]s and [[fossil fuel]]s. Geologists also study the [[history of the Earth]]. Some of the important [[event]]s in the Earth's history are [[flood]]s, [[volcano|volcanic eruptions]], [[earthquake]]s, [[orogeny]] (mountain building), and [[plate tectonics]] (movement of [[continents]]). == Subjects == Geology is divided into special subjects that study one part of geology. Some of these subjects and what they focus on are: * [[Geomorphology]] – the shape of Earth's surface (its ''morphology'') * [[Historical geology]] – the events that shaped the Earth over the last 4.5 billion years * [[Aquifer|Hydrogeology]] – underground water * [[Palaeontology]] – [[fossil]]s; evolutionary histories * [[Petrology]] – [[Rock (geology)|rocks]], how they form, where they are from, and what that implies * [[Mineralogy]] – [[mineral]]s * [[Sedimentology]] – sediments (clays, sands, gravels, soils, etc.) * [[Stratigraphy]] – layered [[sedimentary rock]]s and how they were deposited * Petroleum geol