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Age of oceanic lithosphere
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists, who usually study geophysics, physics, or one of the Earth sciences at the graduate level, complete investigations across a wide range of scientific disciplines. The term geophysics classically refers to solid earth applications: Earth's shape; its gravitational, magnetic fields, and electromagnetic fields ; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. However, modern geophysics organizations and pure scientists use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and 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 lodestones, while more modern magnetic compasses played an important role in the history of navigation. The first seismic instrument was built in 132 AD. Isaac Newton applied his theory of mechanics to the tides and the 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...)
Selected general articles
Image 2
The internal structure of Earth
Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 20% of Earth's radius or 70% of the Moon's radius.
There are no samples of the core accessible for direct measurement, as there are for Earth's mantle. The characteristics of the core have been deduced mostly from measurements of seismic waves and Earth's magnetic field. The inner core is believed to be composed of an iron–nickel alloy with some other elements. The temperature at its surface is estimated to be approximately 5,700 K (5,430 °C; 9,800 °F), about the temperature at the surface of the Sun. (Full article...)- [](/wiki/File:Blank.png "Image 3 Animation of tsunami triggered by the 2004 Indian Ocean earthquake Seismology (/saɪzˈmɒlədʒi, saɪs-/; from Ancient Greek σεισμός (seismós) meaning "earthquake" and -λογία (-logía) meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic waves through planetary bodies. It also includes studies of the environmental effects of earthquakes such as tsunamis; other seismic sources such as volcanoes, plate tectonics, glaciers, rivers, oceanic microseisms, and the atmosphere; and artificial processes such as explosions. Paleoseismology is a related field that uses geology to infer information regarding past earthquakes. A recording of Earth's motion as a function of time, created by a seismograph is called a seismogram. A seismologist is a scientist who works in basic or applied seismology. (Full article...)")
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Radiocarbon dating helped verify the authenticity of the Dead Sea scrolls.
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.
The method was developed in the late 1940s at the University of Chicago by Willard Libby. It is based on the fact that radiocarbon (14
C) is constantly being created in the Earth's atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14
C combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire 14
C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and thereafter the amount of 14
C it contains begins to decrease as the 14
C undergoes radioactive decay. Measuring the amount of 14
C in a sample from a dead plant or animal, such as a piece of wood or a fragment of bone, provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14
C there is to be detected, and because the half-life of 14
C (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to approximately 50,000 years ago, although special preparation methods occasionally make an accurate analysis of older samples possible. Libby received the Nobel Prize in Chemistry for his work in 1960. (Full article...)- [](/wiki/File:Blank.png "Image 6 Earth's gravity measured by NASA GRACE mission, showing deviations from the theoretical gravity of an idealized, smooth Earth, the so-called Earth ellipsoid. Red shows the areas where gravity is stronger than the smooth, standard value, and blue reveals areas where gravity is weaker (Animated version). The gravity of Earth, denoted by g, is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation). It is a vector quantity, whose direction coincides with a plumb bob and strength or magnitude is given by the norm '"
UNIQ--postMath-00000001-QINU"'. In SI units, this acceleration is expressed in metres per second squared (in symbols, m/s2 or m·s−2) or equivalently in newtons per kilogram (N/kg or N·kg−1). Near Earth's surface, the acceleration due to gravity, accurate to 2 significant figures, is 9.8 m/s2 (32 ft/s2). This means that, ignoring the effects of air resistance, the speed of an object falling freely will increase by about 9.8 metres per second (32 ft/s) every second. This quantity is sometimes referred to informally as little g (in contrast, the gravitational constant G is referred to as big G). (Full article...)")
Image 6
Earth's gravity measured by NASA GRACE mission, showing deviations from the theoretical gravity of an idealized, smooth Earth, the so-called Earth ellipsoid. Red shows the areas where gravity is stronger than the smooth, standard value, and blue reveals areas where gravity is weaker (Animated version).
The gravity of Earth, denoted by g, is the net acceleration that is imparted to objects due to the combined effect of gravitation (from mass distribution within Earth) and the centrifugal force (from the Earth's rotation).
It is a vector quantity, whose direction coincides with a plumb bob and strength or magnitude is given by the norm g = ‖ g ‖ {\displaystyle g=\|{\mathit {\mathbf {g} }}\|}.
In SI units, this acceleration is expressed in metres per second squared (in symbols, m/s2 or m·s−2) or equivalently in newtons per kilogram (N/kg or N·kg−1). Near Earth's surface, the acceleration due to gravity, accurate to 2 significant figures, is 9.8 m/s2 (32 ft/s2). This means that, ignoring the effects of air resistance, the speed of an object falling freely will increase by about 9.8 metres per second (32 ft/s) every second. This quantity is sometimes referred to informally as little g (in contrast, the gravitational constant G is referred to as big G). (Full article...)
Image 7
Figure 1: Tidal interaction between the spiral galaxy NGC 169 and a smaller companion
The tidal force or tide-generating force is a gravitational pull on a body, that differs throughout the gravitational field which the body is in. The different tidal forces at the different parts of a body cause the body to stretch more or less toward the gravitational pull, producing tidal phenomena in the body, such as two tidal bulges, on the far-side staying behind and on the near-side being stretched closer. Commonly this is understood as a result of inertia and the concept of centrifugal force, which only effects it, but does not cause it.
Tidal phenomena include solid-earth tides, tidal locking, breaking apart of celestial bodies and formation of ring systems within the Roche limit, and in extreme cases, spaghettification of objects. It arises because the gravitational field exerted on one body by another is not constant across its parts: the nearer side is attracted more strongly than the farther side. The difference is positive in the near side and negative in the far side, which causes a body to get stretched. Thus, the tidal force is also known as the differential force, residual force, or secondary effect of the gravitational field. (Full article...)
Image 8
Automatic ground penetrating Radar (upGPR) near Swiss Camp (Greenland)
Near-surface geophysics is the use of geophysical methods to investigate small-scale features in the shallow (tens of meters) subsurface. It is closely related to applied geophysics or exploration geophysics. Methods used include seismic refraction and reflection, gravity, magnetic, electric, and electromagnetic methods. Many of these methods were developed for oil and mineral exploration but are now used for a great variety of applications, including archaeology, environmental science, forensic science, military intelligence, geotechnical investigation, treasure hunting, and hydrogeology. In addition to the practical applications, near-surface geophysics includes the study of biogeochemical cycles. (Full article...)
Image 9
Magnetic stripes are the result of reversals of the Earth's field and seafloor spreading. New oceanic crust is magnetized as it forms and then it moves away from the ridge in both directions. The models show a ridge (a) about 5 million years ago (b) about 2 million years ago and (c) in the present.
Paleomagnetism (occasionally palaeomagnetism) is the study of prehistoric Earth's magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called paleomagnetists.
Certain magnetic minerals in rocks can record the direction and intensity of Earth's magnetic field at the time they formed. This record provides information on the past behavior of the geomagnetic field and the past location of tectonic plates. The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool. (Full article...)
Image 13
A picture of Earth and the Moon from Mars. The presence of the Moon (which has about 1/81 the mass of Earth), is slowing Earth's rotation and extending the day by a little under 2 milliseconds every 100 years.
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, with a lower orbital velocity and hence a longer orbital period), and a corresponding slowdown of the primary's rotation. See supersynchronous orbit. The process eventually leads to tidal locking, usually of the smaller body first, and later the larger body (e.g. theoretically with Earth-Moon system 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. These satellites will have a higher and higher orbital velocity and a shorter and shorter orbital period, until a final collision with the primary. See subsynchronous orbit. (Full article...)
Image 16
Temperature profile of inner Earth, schematic view (estimated). The red dashed line shows the minimum temperature for the respective mantle rock to melt. The geothermal gradient remains below the melting temperature of the rock, except in the asthenosphere. Sharp rises occur in the uppermost mantle and at the core–mantle boundary.
Geothermal gradient is the rate of change in temperature with respect to increasing depth in Earth's interior. As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plate boundaries, temperature rises in about 25–30 °C/km (72–87 °F/mi) of depth near the surface in the continental crust. However, in some cases the temperature may drop with increasing depth, especially near the surface, a phenomenon known as inverse or negative geothermal gradient. The effects of weather, the Sun, and season only reach a depth of roughly 10–20 m (33–66 ft).
Strictly speaking, _geo_-thermal necessarily refers to Earth, but the concept may be applied to other planets. In SI units, the geothermal gradient is expressed as °C/km, K/km, or mK/m. These are all equivalent. (Full article...)
Image 19
Simplified model of mantle convection: Whole-mantle convection
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 20
The Chandler wobble or Chandler variation of latitude is a small deviation in the Earth's axis of rotation relative to the solid earth, which was discovered by and named after American astronomer Seth Carlo Chandler in 1891. It amounts to change of about 9 metres (30 ft) in the point at which the axis intersects the Earth's surface and has a period of 433 days. This wobble, which is an astronomical nutation, combines with another wobble with a period of six years, so that the total polar motion varies with a period of about 7 years.
The Chandler wobble is an example of the kind of motion that can occur for a freely rotating object that is not a sphere; this is called a free nutation. Somewhat confusingly, the direction of the Earth's rotation axis relative to the stars also varies with different periods, and these motions—caused by the tidal forces of the Moon and Sun—are also called nutations, except for the slowest, which are precessions of the equinoxes. (Full article...)- [](/wiki/File:Blank.png "Image 21 Precessional movement of Earth. Earth rotates (white arrows) once a day around its rotational axis (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particular, axial precession can refer to the gradual shift in the orientation of Earth's axis of rotation in a cycle of approximately 26,000 years. This is similar to the precession of a spinning top, with the axis tracing out a pair of cones joined at their apices. The term "precession" typically refers only to this largest part of the motion; other changes in the alignment of Earth's axis—nutation and polar motion—are much smaller in magnitude. Earth's precession was historically called the precession of the equinoxes, because the equinoxes moved westward along the ecliptic relative to the fixed stars, opposite to the yearly motion of the Sun along the ecliptic. Historically, the discovery of the precession of the equinoxes is usually attributed in the West to the 2nd-century-BC astronomer Hipparchus. With improvements in the ability to calculate the gravitational force between planets during the first half of the nineteenth century, it was recognized that the ecliptic itself moved slightly, which was named planetary precession, as early as 1863, while the dominant component was named lunisolar precession. Their combination was named general precession, instead of precession of the equinoxes. (Full article...)")
Image 21
Precessional movement of Earth. Earth rotates (white arrows) once a day around its rotational axis (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years
In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particular, axial precession can refer to the gradual shift in the orientation of Earth's axis of rotation in a cycle of approximately 26,000 years. This is similar to the precession of a spinning top, with the axis tracing out a pair of cones joined at their apices. The term "precession" typically refers only to this largest part of the motion; other changes in the alignment of Earth's axis—nutation and polar motion—are much smaller in magnitude.
Earth's precession was historically called the precession of the equinoxes, because the equinoxes moved westward along the ecliptic relative to the fixed stars, opposite to the yearly motion of the Sun along the ecliptic. Historically,
the discovery of the precession of the equinoxes is usually attributed in the West to the 2nd-century-BC astronomer Hipparchus. With improvements in the ability to calculate the gravitational force between planets during the first half of the nineteenth century, it was recognized that the ecliptic itself moved slightly, which was named planetary precession, as early as 1863, while the dominant component was named lunisolar precession. Their combination was named general precession, instead of precession of the equinoxes. (Full article...)
Image 23
Schiehallion's isolated position and symmetrical shape were well-suited to the experiment.
The Schiehallion experiment was an 18th-century experiment to determine the mean density of the Earth. Funded by a grant from the Royal Society, it was conducted in the summer of 1774 around the Scottish mountain of Schiehallion, Perthshire. The experiment involved measuring the tiny deflection of the vertical due to the gravitational attraction of a nearby mountain. Schiehallion was considered the ideal location after a search for candidate mountains, thanks to its isolation and almost symmetrical shape.
The experiment had previously been considered, but rejected, by Isaac Newton as a practical demonstration of his theory of gravitation; however, a team of scientists, notably Nevil Maskelyne, the Astronomer Royal, was convinced that the effect would be detectable and undertook to conduct the experiment. The deflection angle depended on the relative densities and volumes of the Earth and the mountain: if the density and volume of Schiehallion could be ascertained, then so could the density of the Earth. Once this was known, it would in turn yield approximate values for those of the other planets, their moons, and the Sun, previously known only in terms of their relative ratios. (Full article...)- [](/wiki/File:Blank.png "Image 24 The Hollow Moon and the closely related Spaceship Moon are pseudoscientific 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 solid, differentiated interior, with a thin crust, extensive mantle, and a dense core which is significantly smaller (in relative terms) than Earth's. While Hollow Moon hypotheses usually propose the hollow space as the result of natural processes, the related Spaceship Moon hypothesis holds that the Moon is an artifact created by an alien civilization; this belief usually coincides with beliefs in UFOs or ancient astronauts. This idea dates from 1970, when two Soviet authors published a short piece in the popular press speculating that the Moon might be "the creation of alien intelligence"; since then, it has occasionally been endorsed by conspiracy theorists like Jim Marrs and David Icke. (Full article...)")
Image 24
The Hollow Moon and the closely related Spaceship Moon are pseudoscientific 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 solid, differentiated interior, with a thin crust, extensive mantle, and a dense core which is significantly smaller (in relative terms) than Earth's.
While Hollow Moon hypotheses usually propose the hollow space as the result of natural processes, the related Spaceship Moon hypothesis holds that the Moon is an artifact created by an alien civilization; this belief usually coincides with beliefs in UFOs or ancient astronauts. This idea dates from 1970, when two Soviet authors published a short piece in the popular press speculating that the Moon might be "the creation of alien intelligence"; since then, it has occasionally been endorsed by conspiracy theorists like Jim Marrs and David Icke. (Full article...)
Image 25
Cloud-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.
Atmospheric electricity describes the electrical charges in the Earth's atmosphere (or that of another planet). The movement of charge between the Earth's surface, the atmosphere, and the ionosphere is known as the global atmospheric electrical circuit. Atmospheric electricity is an interdisciplinary topic with a long history, involving concepts from electrostatics, atmospheric physics, meteorology and Earth science.
Thunderstorms act as a giant battery in the atmosphere, charging up the electrosphere to about 400,000 volts with respect to the surface. This sets up an electric field throughout the atmosphere, which decreases with increase in altitude. Atmospheric ions created by cosmic rays and natural radioactivity move in the electric field, so a very small current flows through the atmosphere, even away from thunderstorms. Near the surface of the Earth, the magnitude of the field is on average around 100 V/m, oriented such that it drives positive charges down. (Full article...)
Selected geophysicist
- [](/wiki/File:Blank.png "Image 1 Portrait by Joseph Duplessis, 1785 Benjamin Franklin (January 17, 1706 [O.S. January 6, 1705] – April 17, 1790) was an American polymath: a writer, scientist, inventor, statesman, diplomat, printer, publisher and political philosopher. Among the most influential intellectuals of his time, Franklin was one of the Founding Fathers of the United States; a drafter and signer of the Declaration of Independence; and the first postmaster general. Franklin became a successful newspaper editor and printer in Philadelphia, the leading city in the colonies, publishing The Pennsylvania Gazette at age 23. He became wealthy publishing this and Poor Richard's Almanack, which he wrote under the pseudonym "Richard Saunders". After 1767, he was associated with the Pennsylvania Chronicle, a newspaper known for its revolutionary sentiments and criticisms of the policies of the British Parliament and the Crown. He pioneered and was the first president of the Academy and College of Philadelphia, which opened in 1751 and later became the University of Pennsylvania. He organized and was the first secretary of the American Philosophical Society and was elected its president in 1769. He was appointed deputy postmaster-general for the British colonies in 1753, which enabled him to set up the first national communications network. (Full article...)")
Image 1
Benjamin Franklin (January 17, 1706 [O.S. January 6, 1705] – April 17, 1790) was an American polymath: a writer, scientist, inventor, statesman, diplomat, printer, publisher and political philosopher. Among the most influential intellectuals of his time, Franklin was one of the Founding Fathers of the United States; a drafter and signer of the Declaration of Independence; and the first postmaster general.
Franklin became a successful newspaper editor and printer in Philadelphia, the leading city in the colonies, publishing The Pennsylvania Gazette at age 23. He became wealthy publishing this and Poor Richard's Almanack, which he wrote under the pseudonym "Richard Saunders". After 1767, he was associated with the Pennsylvania Chronicle, a newspaper known for its revolutionary sentiments and criticisms of the policies of the British Parliament and the Crown. He pioneered and was the first president of the Academy and College of Philadelphia, which opened in 1751 and later became the University of Pennsylvania. He organized and was the first secretary of the American Philosophical Society and was elected its president in 1769. He was appointed deputy postmaster-general for the British colonies in 1753, which enabled him to set up the first national communications network. (Full article...) - [](/wiki/File:Blank.png "Image 7 Blackett in 1948 Patrick Maynard Stuart Blackett, Baron Blackett (18 November 1897 – 13 July 1974) was an English physicist who received the 1948 Nobel Prize in Physics. In 1925, he was the first person to prove that radioactivity could cause the nuclear transmutation of one chemical element to another. He also made major contributions to the Allied war effort in World War II, advising on military strategy and developing operational research. In the war's aftermath, Blackett continued his scientific work, but also became outspoken on political matters. He advocated for restraints on the military use of atomic energy. He was a proponent for Third World development and for reducing the gap between rich and poor. In the 1950s and '60s, he was a key advisor to the Labour Party on science and technology policy. By the time of his death in 1974, Blackett had become controversial to the point that the Times obituary referred to him as the "Radical Nobel-Prize Winning Physicist". (Full article...)")
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Patrick Maynard Stuart Blackett, Baron Blackett (18 November 1897 – 13 July 1974) was an English physicist who received the 1948 Nobel Prize in Physics. In 1925, he was the first person to prove that radioactivity could cause the nuclear transmutation of one chemical element to another. He also made major contributions to the Allied war effort in World War II, advising on military strategy and developing operational research.
In the war's aftermath, Blackett continued his scientific work, but also became outspoken on political matters. He advocated for restraints on the military use of atomic energy. He was a proponent for Third World development and for reducing the gap between rich and poor. In the 1950s and '60s, he was a key advisor to the Labour Party on science and technology policy. By the time of his death in 1974, Blackett had become controversial to the point that the Times obituary referred to him as the "Radical Nobel-Prize Winning Physicist". (Full article...)
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Eugene Newman Parker (June 10, 1927 – March 15, 2022) was an American solar and plasma physicist. In the 1950s he proposed the existence of the solar wind and that the magnetic field in the outer Solar System would be in the shape of a Parker spiral, predictions that were later confirmed by spacecraft measurements. In 1987, Parker proposed the existence of nanoflares, a leading candidate to explain the coronal heating problem.
Parker obtained his PhD from Caltech and spent four years as a postdoctoral researcher at the University of Utah. He joined University of Chicago in 1955 and spent the rest of his career there, holding positions in the physics department, the astronomy and astrophysics department, and the Enrico Fermi Institute. Parker was elected to the National Academy of Sciences in 1967. In 2017, NASA named its Parker Solar Probe in his honor, the first NASA spacecraft named after a living person. (Full article...)- [](/wiki/File:Blank.png "Image 10 Portrait by Christian Albrecht Jensen, 1840 (copy from Gottlieb Biermann, 1887) Johann Carl Friedrich Gauss (/ɡaʊs/; German: Gauß [kaʁl ˈfʁiːdʁɪç ˈɡaʊs] ⓘ; Latin: Carolus Fridericus Gauss; 30 April 1777 – 23 February 1855) was a German mathematician, astronomer, geodesist, and physicist who contributed to many fields in mathematics and science. He was director of the Göttingen Observatory and professor of astronomy from 1807 until his death in 1855. He is widely considered one of the greatest mathematicians of all time. While studying at the University of Göttingen, he propounded several mathematical theorems. Gauss completed his masterpieces Disquisitiones Arithmeticae and Theoria motus corporum coelestium as a private scholar. He gave the second and third complete proofs of the fundamental theorem of algebra, made contributions to number theory, and developed the theories of binary and ternary quadratic forms. (Full article...)")
- [](/wiki/File:Blank.png "Image 11 Broecker c. 2010 Wallace "Wally" Smith Broecker (November 29, 1931 – February 18, 2019) was an American geochemist. He was the Newberry Professor in the Department of Earth and Environmental Sciences at Columbia University, a scientist at Columbia's Lamont–Doherty Earth Observatory and a sustainability fellow at Arizona State University. He developed the idea of a global "conveyor belt" linking the circulation of the global ocean and made major contributions to the science of the carbon cycle and the use of chemical tracers and isotope dating in oceanography. Broecker popularized the term "global warming". He received the Crafoord Prize and the Vetlesen Prize. (Full article...)")
- [](/wiki/File:Blank.png "Image 12 Wegener, c. 1924–1930 Alfred Lothar Wegener (/ˈveɪɡənər/; German: [ˈʔalfʁeːt ˈveːɡənɐ]; 1 November 1880 – November 1930) was a German climatologist, geologist, geophysicist, meteorologist, and polar researcher. During his lifetime he was primarily known for his achievements in meteorology and as a pioneer of polar research, but today he is most remembered as the originator of continental drift hypothesis by suggesting in 1912 that the continents are slowly drifting around the Earth (German: Kontinentalverschiebung). (Full article...)")
Image 14
A stamp of Zhang Heng issued by China Post in 1955
Zhang Heng (Chinese: 張衡; AD 78–139), formerly romanized Chang Heng, was a Chinese polymathic scientist and statesman who lived during the Eastern Han dynasty. Educated in the capital cities of Luoyang and Chang'an, he achieved success as an astronomer, mathematician, seismologist, hydraulic engineer, inventor, geographer, cartographer, ethnographer, artist, poet, philosopher, politician, and literary scholar.
Zhang Heng began his career as a minor civil servant in Nanyang. Eventually, he became Chief Astronomer, Prefect of the Majors for Official Carriages, and then Palace Attendant at the imperial court. His uncompromising stance on historical and calendrical issues led to his becoming a controversial figure, preventing him from rising to the status of Grand Historian. His political rivalry with the palace eunuchs during the reign of Emperor Shun (r. 125–144) led to his decision to retire from the central court to serve as an administrator of Hejian Kingdom in present-day Hebei. Zhang returned home to Nanyang for a short time, before being recalled to serve in the capital once more in 138. He died there a year later, in 139. (Full article...)- [](/wiki/File:Blank.png "Image 17 Bust of Shen at the Beijing Ancient Observatory Shen Kuo (Chinese: 沈括; 1031–1095) or Shen Gua, courtesy name Cunzhong (存中) and pseudonym Mengqi (now usually given as Mengxi) Weng (夢溪翁), was a Chinese polymath, scientist, and statesman of the Song dynasty (960–1279). Shen was a master in many fields of study including mathematics, optics, and horology. In his career as a civil servant, he became a finance minister, governmental state inspector, head official for the Bureau of Astronomy in the Song court, Assistant Minister of Imperial Hospitality, and also served as an academic chancellor. At court his political allegiance was to the Reformist faction known as the New Policies Group, headed by Chancellor Wang Anshi (1021–1085). In his Dream Pool Essays or Dream Torrent Essays (夢溪筆談; Mengxi Bitan) of 1088, Shen was the first to describe the magnetic needle compass, which would be used for navigation (first described in Europe by Alexander Neckam in 1187). Shen discovered the concept of true north in terms of magnetic declination towards the north pole, with experimentation of suspended magnetic needles and "the improved meridian determined by Shen's [astronomical] measurement of the distance between the pole star and true north". This was the decisive step in human history to make compasses more useful for navigation, and may have been a concept unknown in Europe for another four hundred years (evidence of German sundials made circa 1450 show markings similar to Chinese geomancers' compasses in regard to declination). (Full article...)")
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Shen Kuo (Chinese: 沈括; 1031–1095) or Shen Gua, courtesy name Cunzhong (存中) and pseudonym Mengqi (now usually given as Mengxi) Weng (夢溪翁), was a Chinese polymath, scientist, and statesman of the Song dynasty (960–1279). Shen was a master in many fields of study including mathematics, optics, and horology. In his career as a civil servant, he became a finance minister, governmental state inspector, head official for the Bureau of Astronomy in the Song court, Assistant Minister of Imperial Hospitality, and also served as an academic chancellor. At court his political allegiance was to the Reformist faction known as the New Policies Group, headed by Chancellor Wang Anshi (1021–1085).
In his Dream Pool Essays or Dream Torrent Essays (夢溪筆談; Mengxi Bitan) of 1088, Shen was the first to describe the magnetic needle compass, which would be used for navigation (first described in Europe by Alexander Neckam in 1187). Shen discovered the concept of true north in terms of magnetic declination towards the north pole, with experimentation of suspended magnetic needles and "the improved meridian determined by Shen's [astronomical] measurement of the distance between the pole star and true north". This was the decisive step in human history to make compasses more useful for navigation, and may have been a concept unknown in Europe for another four hundred years (evidence of German sundials made circa 1450 show markings similar to Chinese geomancers' compasses in regard to declination). (Full article...) - [](/wiki/File:Blank.png "Image 19 Henry Cavendish FRS (/ˈkævəndɪʃ/ KAV-ən-dish; 10 October 1731 – 24 February 1810) was an English 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 19
Henry Cavendish FRS ( KAV-ən-dish; 10 October 1731 – 24 February 1810) was an English 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...)
Selected images
Image 1Variations in virtual axial dipole moment since the last reversal (from Earth's magnetic field)
Image 2A model of short-wavelength features of Earth's magnetic field, attributed to lithospheric anomalies (from Earth's magnetic field)
Image 3Example 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)
Image 4Animation of tsunami triggered by the 2004 Indian Ocean earthquake (from Seismology)
Image 5World 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)
Image 6A 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)
Image 7Geological cross section of Earth, showing the different layers of the interior. (from Internal structure of Earth)
Image 8A 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)
Image 9Schematic 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)
Image 10The movement of Earth's North Magnetic Pole across the Canadian arctic (from Earth's magnetic field)
Image 11Computer 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)
Image 12Lightning sequence (Duration: 0.32 seconds) (from Atmospheric electricity)
Image 13A 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)
Image 14Cloud-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)
Image 15Computer simulation of the Earth's magnetic field in a period of normal polarity between reversals (from Geophysics)
Image 16Ale's Stones at Kåseberga, around ten kilometres south east of Ystad, Sweden were dated back to approximately 1,400 years ago using the carbon-14 method on organic material found at the site. (from Radiometric dating)
Image 17A 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)
Image 18Estimated declination contours by year, 1590 to 1990 (click to see variation) (from Earth's magnetic field)
Image 19Age of the sea floor. Much of the dating information comes from magnetic anomalies.
Image 20Declination (from Earth's magnetic field)
Image 21Background: a set of traces from magnetic observatories showing a magnetic 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 23A model of thermal convection in the Earth's mantle. The thin red columns are mantle plumes.
Image 24Earth's crust and mantle, Mohorovičić discontinuity between bottom of crust and solid uppermost mantle (from Internal structure of Earth)
Image 25Installation for a temporary seismic station, north Iceland highland. (from Seismology)
Image 26Relationship 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)
Image 27Lu-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)
Image 28Example of a quadrupole field. This can also be constructed by moving two dipoles together. (from Earth's magnetic field)
Image 29An 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)
Image 30Apatite crystals are widely used in fission track dating. (from Radiometric dating)
Image 31Intensity (from Earth's magnetic field)
Image 32Inclination (from Earth's magnetic field)
Image 34Common coordinate systems used for representing the Earth's magnetic field (from Earth's magnetic field)
Image 35A 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)
Image 36Strength of the axial dipole component of Earth's magnetic field from 1600 to 2020 (from Earth's magnetic field)
Image 37Geomagnetic polarity during the late Cenozoic 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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Did you know ...?
- ... that the Gregory Rift in East Africa contains the world's only active carbonatite volcano, Ol Doinyo Lengai (pictured)?
- ...that one way to calculate distances in terms of latitude and longitude is the Haversine formula?
- ...that the supercontinent Pannotia only lasted about sixty million years before disintegrating into four continents?
- ... that the 2002 Sumatra earthquake is considered to be a foreshock of the 2004 Indian Ocean earthquake?
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)