Portal:Geophysics
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The Geophysics Portal
Age of oceanic lithosphere
solar-terrestrial physics; and analogous problems associated with the Moon and other planets.
Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times. The first magnetic compasses were made from
precession of the equinox; and instruments were developed to measure the Earth's shape, density and gravity field, as well as the components of the water cycle. In the 20th century, geophysical methods were developed for remote exploration of the solid Earth and the ocean, and geophysics played an essential role in the development of the theory of plate tectonics. (Full article...
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Selected general articles
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Image 5Theprecessions of the equinoxes. (Full article...)
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Image 9In )
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Image 13potassium–argon dating and uranium–lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. (Full article...)
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Image 15earthquakes, faulting. It also attempts to probe the internal activity by measuring magnetic fields, gravity, and seismic waves, as well as the mineralogy of rocks and their isotopic composition. Methods of geodynamics are also applied to exploration of other planets. (Full article...)
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Image 16Image 17geodynamo and related phenomena.)
Laboratory work in mineral physics require high pressure measurements. The most common tool is a diamond anvil cell, which uses diamonds to put a small sample under pressure that can approach the conditions in the Earth's interior. (Full article...Image 18
Mantle convection is the very slow creep of Earth's solid silicate mantle as convection currents carry heat from the interior to the planet's surface. Mantle convection causes tectonic plates to move around the Earth's surface.
The Earth's lithosphere rides atop the asthenosphere, and the two form the components of the upper mantle. The lithosphere is divided into tectonic plates that are continuously being created or consumed at plate boundaries. Accretion occurs as mantle is added to the growing edges of a plate, associated with seafloor spreading. Upwelling beneath the spreading centers is a shallow, rising component of mantle convection and in most cases not directly linked to the global mantle upwelling. The hot material added at spreading centers cools down by conduction and convection of heat as it moves away from the spreading centers. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of subduction usually at an oceanic trench. Subduction is the descending component of mantle convection. (Full article...)Image 19Image 20Image 21
Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite (e.g. the Moon) and the primary planet that it orbits (e.g. Earth). The acceleration causes a gradual recession of a satellite in a prograde orbit (satellite moving to a higher orbit, away from the primary body), and a corresponding slowdown of the primary's rotation. The process eventually leads to tidal locking, usually of the smaller body first, and later the larger body (e.g. theoretically with Earth in 50 billion years). The Earth–Moon system is the best-studied case.
The similar process of tidal deceleration occurs for satellites that have an orbital period that is shorter than the primary's rotational period, or that orbit in a retrograde direction. (Full article...)Image 22Image 23Infigure depends on application, including the precision needed for the model. A spherical Earth is a well-known historical approximation that is satisfactory for geography, astronomy and many other purposes. Several models with greater accuracy (including ellipsoid) have been developed so that coordinate systems can serve the precise needs of navigation, surveying, cadastre, land use, and various other concerns. (Full article...)Image 24Thepseudoscientific hypotheses that propose that Earth's Moon is either wholly hollow or otherwise contains a substantial interior space. No scientific evidence exists to support the idea; seismic observations and other data collected since spacecraft began to orbit or land on the Moon indicate that it has a thin crust, extensive mantle and small, dense core. Overall it is much less dense than Earth.)
The concept of a (partially) hollow Moon has been employed in science fiction multiple times, starting with H. G. Wells' 1901 novel The First Men in the Moon.' I (Full article...Image 25Selected geophysicist
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Henry Cavendish FRS (/ˈkævəndɪʃ/ KAV-ən-dish; 10 October 1731 – 24 February 1810) was an English natural philosopher and scientist who was an important experimental and theoretical chemist and physicist. He is noted for his discovery of hydrogen, which he termed "inflammable air". He described the density of inflammable air, which formed water on combustion, in a 1766 paper, On Factitious Airs. Antoine Lavoisier later reproduced Cavendish's experiment and gave the element its name.
A shy man, Cavendish was distinguished for great accuracy and precision in his researches into the composition of atmospheric air, the properties of different gases, the synthesis of water, the law governing electrical attraction and repulsion, a mechanical theory of heat, and calculations of the density (and hence the mass) of the Earth. His experiment to measure the density of the Earth (which, in turn, allows the gravitational constant to be calculated) has come to be known as the Cavendish experiment. (Full article...)Image 9Image 10Image 11Richard Doell (1923 – March 6, 2008) was a distinguished American scientist known for developing the time scale for geomagnetic reversals with Allan V. Cox and Brent Dalrymple. This work was a major step in the development of plate tectonics. Doell shared the Vetlesen Prize with Cox and Dalrymple. (Full article...)Image 12
Andrija Mohorovičić (23 January 1857 – 18 December 1936) was a Croatian geophysicist. He is best known for the eponymous Mohorovičić discontinuity and is considered one of the founders of modern seismology. (Full article...)Image 13Image 14Image 15
Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 1769 – 6 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister, philosopher, and linguist Wilhelm von Humboldt (1767–1835). Humboldt's quantitative work on botanical geography laid the foundation for the field of biogeography, while his advocacy of long-term systematic geophysical measurement pioneered modern geomagnetic and meteorological monitoring.
Between 1799 and 1804, Humboldt travelled extensively in the Americas, exploring and describing them for the first time from a non-Spanish European scientific point of view. His description of the journey was written up and published in several volumes over 21 years. Humboldt was one of the first people to propose that the lands bordering the Atlantic Ocean were once joined (South America and Africa in particular). (Full article...)Image 16Image 17Image 18Image 19Selected images
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Image 1A schematic illustrating the relationship between motion of conducting fluid, organized into rolls by the Coriolis force, and the magnetic field the motion generates. (from Earth's magnetic field)
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Image 2The movement of Earth's North Magnetic Pole across the Canadian arctic (from Earth's magnetic field)
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Image 3Earth's crust and mantle, Mohorovičić discontinuity between bottom of crust and solid uppermost mantle (from Internal structure of Earth)
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Image 4Common coordinate systems used for representing the Earth's magnetic field (from Earth's magnetic field)
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Image 5Lightning sequence (Duration: 0.32 seconds) (from Atmospheric electricity)
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Image 6Geological cross section of Earth, showing its internal structure, the atmosphere and hydrosphere. (from Internal structure of Earth)
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Image 7Strength of the axial dipole component of Earth's magnetic field from 1600 to 2020 (from Earth's magnetic field)
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Image 8A model of short-wavelength features of Earth's magnetic field, attributed to lithospheric anomalies (from Earth's magnetic field)
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Image 10Installation for a temporary seismic station, north Iceland highland. (from Seismology)
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Image 11Background: a set of traces from magnetic observatories showing amagnetic storm in 2000.)
Globe: map showing locations of observatories and contour lines giving horizontal magnetic intensity in μ T. (from Earth's magnetic field -
Image 12Thermal ionization mass spectrometer used in radiometric dating. (from Radiometric dating)
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Image 13Example of a quadrupole field. This can also be constructed by moving two dipoles together. (from Earth's magnetic field)
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Image 14Computer simulation of Earth's field in a period of normal polarity between reversals. 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. (from Earth's magnetic field)
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Image 15Relationship between Earth's poles. A1 and A2 are the geographic poles; B1 and B2 are the geomagnetic poles; C1 (south) and C2 (north) are the magnetic poles. (from Earth's magnetic field)
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Image 16Ale's Stones at Kåseberga, around ten kilometres south east of Ystad, Sweden were dated at 56 CE using the carbon-14 method on organic material found at the site. (from Radiometric dating)
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Image 17An artist's rendering of the structure of a magnetosphere. 1) Bow shock. 2) Magnetosheath. 3) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere. (from Earth's magnetic field)
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Image 18A depiction of atmospheric electricity in a Martian dust storm, which has been suggested as a possible explanation for enigmatic chemistry results from Mars (see also Viking lander biological experiments) (from Atmospheric electricity)
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Image 19A diagram of Earth's geodynamo and magnetic field, which could have been driven in Earth's early history by the crystallization of magnesium oxide, silicon dioxide, and iron(II) oxide (from Internal structure of Earth)
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Image 20World map showing frequency of lightning strikes, in flashes per km2 per year (equal-area projection). Lightning strikes most frequently in the Democratic Republic of the Congo. Combined 1995–2003 data from the Optical Transient Detector and 1998–2003 data from the Lightning Imaging Sensor. (from Atmospheric electricity)
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Image 21Geomagnetic polarity during the lateCenozoic Era. Dark areas denote periods where the polarity matches today's polarity, light areas denote periods where that polarity is reversed. (from Earth's magnetic field)
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Image 22Cloud-to-ground lightning. Typically, lightning discharges 30,000 amperes, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays. Plasma temperatures in lightning can approach 28,000 kelvins. (from Atmospheric electricity)
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Image 23Lu-Hf isochrons plotted of meteorite samples. The age is calculated from the slope of the isochron (line) and the original composition from the intercept of the isochron with the y-axis. (from Radiometric dating)
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Image 24A photograph of Earth taken by the crew of Apollo 17 in 1972. A processed version became widely known as The Blue Marble. (from Internal structure of Earth)
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Image 25Variations in virtual axial dipole moment since the last reversal (from Earth's magnetic field)
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Image 26Estimated declination contours by year, 1590 to 1990 (click to see variation) (from Earth's magnetic field)
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Image 28Age of the sea floor. Much of the dating information comes from magnetic anomalies.
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Image 29Schematic representation of spherical harmonics on a sphere and their nodal lines. Pℓ m is equal to 0 along m great circles passing through the poles, and along ℓ-m circles of equal latitude. The function changes sign each ℓtime it crosses one of these lines. (from Earth's magnetic field)
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Image 30Example of a radioactive decay chain from lead-212 (212Pb) to lead-208 (208Pb) . Each parent nuclide spontaneously decays into a daughter nuclide (the decay product) via an α decay or a β− decay. The final decay product, lead-208 (208Pb), is stable and can no longer undergo spontaneous radioactive decay. (from Radiometric dating)
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Image 32A concordia diagram as used in uranium–lead dating, with data from the Pfunze Belt, Zimbabwe. All the samples show loss of lead isotopes, but the intercept of the errorchron (straight line through the sample points) and the concordia (curve) shows the correct age of the rock. (from Radiometric dating)
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Image 33A model ofmantle plumes.
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Image 34Computer simulation of the Earth's magnetic field in a period of normal polarity between reversals (from Geophysics)
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Did you know ...?
- ... that most of the Bangui Magnetic Anomaly (pictured as large red anomaly in central Africa), the result of an igneous intrusion or meteoriteimpact?
- ... that 47 terrawatts of heat emerges from the interior of the Earth compared to 173,000 terrawatts received from the sun?
- ... that Cleopatra?
- ... that the Marlborough Fault System, and carry most of the displacement on the Australian-Pacific plate boundary in northern South Island?
- ... that a auroral beam", a "blood red" sky, and a "luminous mass, shaped somewhat like a torpedo"?
In the news
- 5 December 2019: Earthquakes on the Cascadia Fault may trigger earthquakes on the San Andreas Fault (Nature)
- 10 December 2019/ 20 January 2020: New evidence suggests Earth's magnetic field was present 3.7 billion years ago (Nature) - or perhaps even 4.2 billion years ago (Science)
- 13 January 2020: Brazil opens "spectacular" research base in Antarctica (Science)
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