Earth science orgeoscience includes all fields ofnatural science related to the planetEarth.[1] This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres: thebiosphere,hydrosphere/cryosphere,atmosphere, andgeosphere (orlithosphere). Earth science can be considered to be a branch ofplanetary science but with a much older history.
Geology is broadly the study of Earth's structure, substance, and processes. Geology is largely the study of thelithosphere, or Earth's surface, including thecrust androcks. It includes the physical characteristics and processes that occur in the lithosphere as well as how they are affected bygeothermal energy. It incorporates aspects of chemistry, physics, and biology as elements of geology interact.Historical geology is the application of geology to interpretEarth history and how it has changed over time.
Geochemistry studies the chemical components and processes of the Earth.Geophysics studies the physical properties of the Earth.Paleontology studies fossilized biological material in the lithosphere.Planetary geology studies geoscience as it pertains to extraterrestrial bodies.Geomorphology studies the origin of landscapes.Structural geology studies the deformation of rocks to produce mountains and lowlands. Resource geology studies how energy resources can be obtained from minerals.Environmental geology studies how pollution and contaminants affect soil and rock.[2]Mineralogy is the study of minerals and includes the study of mineral formation,crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals.[3]Petrology is the study of rocks, including the formation and composition of rocks.Petrography is a branch of petrology that studies the typology and classification of rocks.[4]
Plate tectonics,mountain ranges,volcanoes, andearthquakes aregeological phenomena that can be explained in terms of physical and chemical processes in the Earth's crust.[6] Beneath the Earth's crust lies themantle which is heated by theradioactive decay ofheavy elements. The mantle is not quite solid and consists ofmagma which is in a state of semi-perpetualconvection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics.[7][8][9][10] Areas of the crust where new crust is created are calleddivergent boundaries, those where it is brought back into the Earth areconvergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to astransform (or conservative) boundaries.[8][10][11]Earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction.[12]
Plate tectonics might be thought of as the process by which the Earth is resurfaced. As the result ofseafloor spreading, new crust and lithosphere is created by the flow of magma from themantle to the near surface, through fissures, where it cools and solidifies. Throughsubduction, oceanic crust and lithosphere vehemently returns to the convecting mantle.[8][10][13] Volcanoes result primarily from the melting of subducted crust material. Crust material that is forced into theasthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface—giving birth to volcanoes.[8][12]
Thetroposphere,stratosphere,mesosphere,thermosphere, andexosphere are the five layers which make up Earth's atmosphere. 75% of the mass in the atmosphere is located within the troposphere, the lowest layer. In all, the atmosphere is made up of about 78.0%nitrogen, 20.9%oxygen, and 0.92%argon, and small amounts of other gases including CO2 and water vapor.[15] Water vapor and CO2 cause the Earth's atmosphere to catch and hold the Sun's energy through thegreenhouse effect.[16] This makes Earth's surface warm enough for liquid water and life. In addition to trapping heat, the atmosphere also protects living organisms by shielding the Earth's surface fromcosmic rays.[17] Themagnetic field—created by the internal motions of the core—produces themagnetosphere which protects Earth's atmosphere from thesolar wind.[18] As the Earth is4.5 billion years old,[19][20] it would have lost its atmosphere by now if there were no protective magnetosphere.
Computer simulation ofEarth's field in a period of normal polarity between reversals.[21] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of Earth is centered and vertical. The dense clusters of lines are within Earth's core.[22]
The magnitude of Earth's magnetic field at its surface ranges from 25 to 65 μT (0.25 to 0.65 G).[23] As an approximation, it is represented by a field of amagnetic dipole currently tilted at an angle of about 11° with respect toEarth's rotational axis, as if there were an enormousbar magnet placed at that angle through the center of Earth. TheNorth geomagnetic pole (Ellesmere Island,Nunavut, Canada) actually represents the South pole of Earth's magnetic field, and conversely theSouth geomagnetic pole corresponds to the north pole of Earth's magnetic field (because opposite magnetic poles attract and the north end of a magnet, like a compass needle, points toward Earth's South magnetic field.)
While the North and Southmagnetic poles are usually located near the geographic poles, they slowly and continuously move over geological time scales, but sufficiently slowly for ordinarycompasses to remain useful for navigation. However, at irregular intervals averaging several hundred thousand years,Earth's field reverses and theNorth andSouth Magnetic Poles abruptly switch places. These reversals of thegeomagnetic poles leave a record in rocks that are of value topaleomagnetists in calculating geomagnetic fields in the past. Such information in turn is helpful in studying the motions of continents and ocean floors. Themagnetosphere is defined by the extent of Earth's magnetic field in space orgeospace. It extends above theionosphere, several tens of thousands of kilometres intospace, protecting Earth from the charged particles of thesolar wind andcosmic rays that would otherwise strip away the upper atmosphere, including theozone layer that protects Earth fromharmful ultraviolet radiation.
Hydrology is the study of the hydrosphere and themovement of water on Earth. It emphasizes the study of how humans use and interact with freshwater supplies. Study of water's movement is closely related togeomorphology and other branches of Earth science. Applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. Subdisciplines of hydrology includeoceanography,hydrogeology,ecohydrology, andglaciology. Oceanography is the study of oceans.[24] Hydrogeology is the study ofgroundwater. It includes the mapping of groundwater supplies and the analysis of groundwater contaminants. Applied hydrogeology seeks to prevent contamination of groundwater andmineral springs and make it available asdrinking water. The earliest exploitation of groundwater resources dates back to 3000 BC, and hydrogeology as a science was developed by hydrologists beginning in the 17th century.[25] Ecohydrology is the study of ecological systems in thehydrosphere. It can be divided into the physical study of aquatic ecosystems and the biological study of aquatic organisms. Ecohydrology includes the effects that organisms and aquatic ecosystems have on one another as well as how these ecoystems are affected by humans.[26] Glaciology is the study of the cryosphere, includingglaciers and coverage of the Earth by ice and snow. Concerns of glaciology include access to glacial freshwater, mitigation of glacial hazards, obtaining resources that exist beneath frozen land, and addressing the effects of climate change on the cryosphere.[27]
Ecology is the study of thebiosphere. This includes the study of nature and of how living things interact with the Earth and one another and the consequences of that. It considers how living things use resources such asoxygen,water, andnutrients from the Earth to sustain themselves. It also considers how humans and other living creatures cause changes to nature.[28]
Physical geography is the study ofEarth's systems and how they interact with one another as part of a single self-contained system. It incorporates astronomy, mathematical geography, meteorology, climatology, geology, geomorphology, biology, biogeography, pedology, and soils geography. Physical geography is distinct fromhuman geography, which studies the human populations on Earth, though it does include human effects on the environment.[29]
Methodologies vary depending on the nature of the subjects being studied. Studies typically fall into one of three categories: observational, experimental, or theoretical. Earth scientists often conduct sophisticated computer analysis or visit an interesting location to study earth phenomena (e.g. Antarctica orhot spot island chains).
A foundational idea in Earth science is the notion ofuniformitarianism, which states that "ancient geologic features are interpreted by understanding active processes that are readily observed." In other words, any geologic processes at work in the present have operated in the same ways throughout geologic time. This enables those who studyEarth history to apply knowledge of how the Earth's processes operate in the present to gain insight into how the planet has evolved and changed throughout long history.
In Earth science, it is common to conceptualize the Earth's surface as consisting of several distinct layers, often referred to as spheres: thelithosphere, thehydrosphere, theatmosphere, and thebiosphere, this concept of spheres is a useful tool for understanding the Earth's surface and its various processes[30] these correspond torocks,water,air andlife. Also included by some are thecryosphere (corresponding toice) as a distinct portion of the hydrosphere and thepedosphere (corresponding tosoil) as an active and intermixed sphere.The followingfields of science are generally categorized within the Earth sciences:
Geochemistry studies the processes that control the abundance, composition, and distribution of chemical compounds and isotopes in geologic environments. Geochemists use the tools and principles of chemistry to study the Earth's composition, structure, processes, and other physical aspects. Major subdisciplines areaqueous geochemistry,cosmochemistry,isotope geochemistry andbiogeochemistry.
Ecology covers the interactions between organisms and their environment. This field of study differentiates the study of Earth from other planets in theSolar System, Earth being the only planet teeming with life.
Hydrology,oceanography andlimnology are studies which focus on the movement, distribution, and quality of the water and involve all the components of the hydrologic cycle on the Earth and its atmosphere (orhydrosphere). "Sub-disciplines of hydrology include hydrometeorology, surface water hydrology, hydrogeology, watershed science, forest hydrology, and water chemistry."[37]
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