Geology (from the Ancient Greek γῆ, ("earth") and -λoγία, -logia, ("study of", "discourse")[1][2]) is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology significantly overlaps all other earth sciences, including hydrology and the atmospheric sciences, and so is treated as one major aspect of integrated earth system science and planetary science.

An 1875 geological map of Europe, compiled by the Belgian geologist André Dumont (colors indicate the distribution of rocks of different ages and types across the continent, as they were known then)
Aerial view of Grand Prismatic Spring; Hot Springs, Midway & Lower Geyser Basin, Yellowstone National Park.

Geology describes the structure of the Earth on and beneath its surface, and the processes that have shaped that structure. It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks.[3] By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, and also to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates.

Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, and numerical modelling. In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, and providing insights into past climate change. Geology is a major academic discipline, and it plays an important role in geotechnical engineering.

Sarychev Peak Volcano erupts June 12, 2009, on Matua Island.

Geologic materials

The majority of geological data comes from research on solid Earth materials. These typically fall into one of two categories: rock and unlithified material.


The rock cycle shows the relationship between igneous, sedimentary, and metamorphic rocks.

The majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous, sedimentary, and metamorphic. The rock cycle illustrates the relationships among them (see diagram).

When a rock solidifies or crystallizes from melt (magma or lava), it is an igneous rock. This rock can be weathered and eroded, then redeposited and lithified into a sedimentary rock. It can then be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric. All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once more solidify.


To study all three types of rock, geologists evaluate the minerals of which they are composed. Each mineral has distinct physical properties, and there are many tests to determine each of them. The specimens can be tested for:[4]

  • Luster: Measurement of the amount of light reflected from the surface. Luster is broken into metallic and nonmetallic.
  • Color: Minerals are grouped by their color. Mostly diagnostic but impurities can change a mineral's color.
  • Streak: Performed by scratching the sample on a porcelain plate. The color of the streak can help name the mineral.
  • Hardness: The resistance of a mineral to scratch.
  • Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along closely spaced parallel planes.
  • Specific gravity: the weight of a specific volume of a mineral.
  • Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing.
  • Magnetism: Involves using a magnet to test for magnetism.
  • Taste: Minerals can have a distinctive taste, like Halite (mineral) (which tastes like table salt).
  • Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs.

Unlithified material

Geologists also study unlithified materials (referred to as drift), which typically come from more recent deposits. These materials are superficial deposits that lie above the bedrock.[5] This study is often known as Quaternary geology, after the Quaternary period of geologic history.

Magma and lava

However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks. The active flow of molten rock is closely studied in volcanology, and igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source.

Other Languages
Afrikaans: Geologie
Alemannisch: Geologie
العربية: جيولوجيا
aragonés: Cheolochía
arpetan: G·eologia
asturianu: Xeoloxía
azərbaycanca: Geologiya
বাংলা: ভূতত্ত্ব
Bân-lâm-gú: Tē-chit-ha̍k
Basa Banyumasan: Geologi
башҡортса: Геология
беларуская: Геалогія
беларуская (тарашкевіца)‎: Геалёгія
भोजपुरी: भूबिज्ञान
Bislama: Jialoji
български: Геология
bosanski: Geologija
brezhoneg: Douarouriezh
català: Geologia
Чӑвашла: Геологи
čeština: Geologie
chiShona: Unenachisi
corsu: Geologia
Cymraeg: Daeareg
dansk: Geologi
Deutsch: Geologie
eesti: Geoloogia
Ελληνικά: Γεωλογία
español: Geología
Esperanto: Geologio
estremeñu: Geologia
euskara: Geologia
Fiji Hindi: Geology
føroyskt: Jarðfrøði
français: Géologie
Frysk: Geology
furlan: Gjeologjie
Gaeilge: Geolaíocht
Gàidhlig: Geòlas
galego: Xeoloxía
한국어: 지질학
Hawaiʻi: Huli honua
हिन्दी: भूविज्ञान
hrvatski: Geologija
Ilokano: Heolohia
Bahasa Indonesia: Geologi
interlingua: Geologia
Interlingue: Geologie
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᓄᓇᓕᕆᓂᖅ
Ирон: Геологи
isiXhosa: IJioloji
íslenska: Jarðfræði
italiano: Geologia
עברית: גאולוגיה
Jawa: Géologi
kalaallisut: Nunarsualerineq
ქართული: გეოლოგია
қазақша: Геология
kernowek: Dororyeth
Kiswahili: Jiolojia
Kreyòl ayisyen: Jewoloji
kurdî: Erdzanî
Кыргызча: Геология
Ladino: Jeolojiya
لۊری شومالی: زمیݩ شناسی
Latina: Geologia
latviešu: Ģeoloģija
Lëtzebuergesch: Geologie
лезги: Геология
lietuvių: Geologija
Limburgs: Geologie
Lingua Franca Nova: Jeolojia
la .lojban.: ligytedyske
lumbaart: Geulugia
magyar: Geológia
македонски: Геологија
Bahasa Melayu: Geologi
Mìng-dĕ̤ng-ngṳ̄: Dê-cék
Mirandés: Geologie
монгол: Геологи
မြန်မာဘာသာ: ဘူမိဗေဒ
Nāhuatl: Tlālmatiliztli
Nederlands: Geologie
नेपाली: जियोलोजी
नेपाल भाषा: भूगर्भशास्त्र
日本語: 地質学
Napulitano: Giuloggia
Nordfriisk: Geologii
Norfuk / Pitkern: Jiolojii
norsk: Geologi
norsk nynorsk: Geologi
Nouormand: Géologie
Novial: Geologia
occitan: Geologia
олык марий: Геологий
Oromoo: Ji'ooloojii
oʻzbekcha/ўзбекча: Geologiya
پنجابی: دھرتی پڑھت
Papiamentu: Geologia
Patois: Jaaloji
Picard: Jolodjie
Piemontèis: Geologìa
Plattdüütsch: Geologie
polski: Geologia
português: Geologia
Qaraqalpaqsha: Geologiya
română: Geologie
русиньскый: Ґеолоґія
русский: Геология
саха тыла: Геология
Scots: Geology
Seeltersk: Geologie
Sesotho: Jeoloji
shqip: Gjeologjia
sicilianu: Gioluggìa
සිංහල: භූවේදය
Simple English: Geology
slovenčina: Geológia
slovenščina: Geologija
کوردی: زەویناسی
српски / srpski: Геологија
srpskohrvatski / српскохрватски: Geologija
Basa Sunda: Géologi
suomi: Geologia
svenska: Geologi
Tagalog: Heolohiya
தமிழ்: நிலவியல்
татарча/tatarça: Геология
тоҷикӣ: Геология
Türkçe: Jeoloji
Türkmençe: Geologiýa
тыва дыл: Геология
Thuɔŋjäŋ: Piööckätöupiny
українська: Геологія
اردو: ارضیات
ئۇيغۇرچە / Uyghurche: گېئولوگىيە
vèneto: Xeołoxia
Tiếng Việt: Địa chất học
Volapük: Talav
Võro: Geoloogia
Winaray: Heolohiya
吴语: 地質學
ייִדיש: געאלאגיע
粵語: 地質學
Zazaki: Cêolociye
žemaitėška: Geuoluogėjė
中文: 地质学