In biology and genetics, the germline in a multicellular organism is the population of its bodily cells that are so differentiated or segregated that in the usual processes of reproduction they may pass on their genetic material to the progeny. As a rule this passing-on happens via a process of sexual reproduction. However, there are many exceptions, including processes and concepts such as various forms of apomixis, automixis, cloning, or parthenogenesis; the cells of the germline are called germ cells. For example, gametes such as the sperm or the egg are part of the germline. So are the cells that divide to produce the gametes, called gametocytes, the cells that produce those, called gametogonia, all the way back to the zygote, the cell from which the individual developed. In sexually reproducing organisms, cells that are not in the germline are called somatic cells. According to this view mutations and other genetic changes in the germline may be passed to offspring, but a change in a somatic cell will not be.
This need not apply to somatically reproducing organisms, such as many plants. For example, many varieties of citrus, plants in the Rosaceae and some in the Asteraceae, such as Taraxacum produce seeds apomictically when somatic diploid cells displace the ovule or early embryo. In an earlier stage of genetic thinking, the distinction between germline and somatic cell was clear cut. For example, August Weismann proposed and pointed out, a germline cell is immortal in the sense that it is part of a lineage that has reproduced indefinitely since the beginning of life and, barring accident could continue doing so indefinitely. However, it is now known in some detail that this distinction between somatic and germ cells is artificial and depends on particular circumstances and internal cellular mechanisms such as telomeres and controls such as the selective application of telomerase in germ cells, stem cells and the like. Not all multicellular organisms differentiate into somatic and germ lines, but in the absence of specialised technical human intervention all but the simplest multicellular structures do so.
In such organisms somatic cells tend to be totipotent, for over a century sponge cells have been known to reassemble into new sponges after having been separated by forcing them through a sieve. Germline can refer to a lineage of cells spanning many generations of individuals—for example, the germline that links any living individual to the hypothetical last universal common ancestor, from which all plants and animals descend. Plants and basal metazoans such as sponges and corals do not sequester a distinct germline, generating gametes from multipotent stem cell lineages that give rise to ordinary somatic tissues, it is therefore that germline sequestration first evolved in complex animals with sophisticated body plans, i.e. bilaterians. There are several theories on the origin of the strict germline-soma distinction. Setting aside an isolated germ cell population early in embryogenesis might promote cooperation between the somatic cells of a complex multicellular organism. Another recent theory suggests that early germline sequestration evolved to limit the accumulation of deleterious mutations in mitochondrial genes in complex organisms with high energy requirements and fast mitochondrial mutation rates.
Reactive oxygen species are produced as byproducts of metabolism. In germline cells, ROS are a significant cause of DNA damages that, upon DNA replication, lead to mutations. 8-Oxoguanine, an oxidized derivative of guanine, is produced by spontaneous oxidation in the germline cells of mice, during the cell’s DNA replication cause GC to TA transversion mutations. Such mutations occur throughout the mouse chromosomes as well as during different stages of gametogenesis; the mutation frequencies for cells in different stages of gametogenesis are about 5 to 10-fold lower than in somatic cells both for spermatogenesis and oogenesis. The lower frequencies of mutation in germline cells compared to somatic cells appears to be due to more efficient DNA repair of DNA damages homologous recombinational repair, during germline meiosis. Among humans, about five percent of live-born offspring have a genetic disorder, of these, about 20% are due to newly arisen germline mutations. August Weismann Epigenetics Germ line development Germinal choice technology Weismann barrier
A planet is an astronomical body orbiting a star or stellar remnant, massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, has cleared its neighbouring region of planetesimals. The term planet is ancient, with ties to history, science and religion. Five planets in the Solar System are visible to the naked eye; these were regarded by many early cultures as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union adopted a resolution defining planets within the Solar System; this definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the modern definition, some celestial bodies, such as Ceres, Pallas and Vesta, Pluto, that were once considered planets by the scientific community, are no longer viewed as such.
The planets were thought by Ptolemy to orbit Earth in epicycle motions. Although the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. About the same time, by careful analysis of pre-telescopic observational data collected by Tycho Brahe, Johannes Kepler found the planets' orbits were elliptical rather than circular; as observational tools improved, astronomers saw that, like Earth, each of the planets rotated around an axis tilted with respect to its orbital pole, some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes and hydrology. Planets are divided into two main types: large low-density giant planets, smaller rocky terrestrials. There are eight planets in the Solar System.
In order of increasing distance from the Sun, they are the four terrestrials, Venus and Mars the four giant planets, Saturn and Neptune. Six of the planets are orbited by one or more natural satellites. Several thousands of planets around other stars have been discovered in the Milky Way; as of 1 April 2019, 4,023 known extrasolar planets in 3,005 planetary systems, ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter have been discovered, out of which more than 100 planets are the same size as Earth, nine of which are at the same relative distance from their star as Earth from the Sun, i.e. in the circumstellar habitable zone. On December 20, 2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A 2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way.
Around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone. The idea of planets has evolved over its history, from the divine lights of antiquity to the earthly objects of the scientific age; the concept has expanded to include worlds not only in the Solar System, but in hundreds of other extrasolar systems. The ambiguities inherent in defining planets have led to much scientific controversy; the five classical planets, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the "fixed stars", which maintained a constant relative position in the sky. Ancient Greeks called these lights πλάνητες ἀστέρες or πλανῆται, from which today's word "planet" was derived. In ancient Greece, China and indeed all pre-modern civilizations, it was universally believed that Earth was the center of the Universe and that all the "planets" circled Earth.
The reasons for this perception were that stars and planets appeared to revolve around Earth each day and the common-sense perceptions that Earth was solid and stable and that it was not moving but at rest. The first civilization known to have a functional theory of the planets were the Babylonians, who lived in Mesopotamia in the first and second millennia BC; the oldest surviving planetary astronomical text is the Babylonian Venus tablet of Ammisaduqa, a 7th-century BC copy of a list of observations of the motions of the planet Venus, that dates as early as the second millennium BC. The MUL. APIN is a pair of cuneiform tablets dating from the 7th century BC that lays out the motions of the Sun and planets over the course of the year; the Babylonian astrologers laid the foundations of what would become Western astrology. The Enuma anu enlil, written during the Neo-Assyrian period in the 7th century BC, comprises a list of omens and their relationships with various celestial phenomena including the motions of the planets.
Venus and the outer planets Mars and Saturn were all identified by Babylonian astronomers. These would remain the only known planets until the invention of the telescope in early modern times; the ancient Greeks did not attach as much significance to the planets as the Babylonians. The Pythagoreans, in the 6th and 5t
A continent is one of several large landmasses of the world. Identified by convention rather than any strict criteria, up to seven regions are regarded as continents. Ordered from largest in area to smallest, they are: Asia, North America, South America, Antarctica and Australia. Geologically, the continents correspond to areas of continental crust that are found on the continental plates. However, some areas of continental crust are regions covered with water not included in the list of continents. Zealandia is one such area. Islands are grouped with a neighbouring continent to divide all the world's land into geopolitical regions. Under this scheme, most of the island countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form a geopolitical region called Oceania. By convention, "continents are understood to be large, discrete masses of land, ideally separated by expanses of water." Several of the seven conventionally recognized continents are not discrete landmasses separated by water.
The criterion "large" leads to arbitrary classification: Greenland, with a surface area of 2,166,086 square kilometres is considered the world's largest island, while Australia, at 7,617,930 square kilometres is deemed the smallest continent. Earth's major landmasses all have coasts on a single, continuous World Ocean, divided into a number of principal oceanic components by the continents and various geographic criteria; the most restricted meaning of continent is that of a continuous area of land or mainland, with the coastline and any land boundaries forming the edge of the continent. In this sense the term continental Europe is used to refer to mainland Europe, excluding islands such as Great Britain, Ireland and Iceland, the term continent of Australia may refer to the mainland of Australia, excluding Tasmania and New Guinea; the continental United States refers to the 48 contiguous states and the District of Columbia in central North America and may include Alaska in the northwest of the continent, while excluding Hawaii, Puerto Rico, Guam in the oceans.
From the perspective of geology or physical geography, continent may be extended beyond the confines of continuous dry land to include the shallow, submerged adjacent area and the islands on the shelf, as they are structurally part of the continent. From this perspective, the edge of the continental shelf is the true edge of the continent, as shorelines vary with changes in sea level. In this sense the islands of Great Britain and Ireland are part of Europe, while Australia and the island of New Guinea together form a continent; as a cultural construct, the concept of a continent may go beyond the continental shelf to include oceanic islands and continental fragments. In this way, Iceland is considered Madagascar part of Africa. Extrapolating the concept to its extreme, some geographers group the Australian continental plate with other islands in the Pacific into one continent called Oceania; this divides the entire land surface of Earth into quasi-continents. The ideal criterion that each continent is a discrete landmass is relaxed due to historical conventions.
Of the seven most globally recognized continents, only Antarctica and Australia are separated from other continents by the ocean. Several continents are defined not as distinct bodies but as "more or less discrete masses of land". Asia and Africa are joined by the Isthmus of Suez, North and South America by the Isthmus of Panama. In both cases, there is no complete separation of these landmasses by water. Both these isthmuses are narrow compared to the bulk of the landmasses they unite. North America and South America are treated as separate continents in the seven-continent model. However, they may be viewed as a single continent known as America or the Americas; this viewpoint was common in the United States until World War II, remains prevalent in some Asian six-continent models. This remains the more common vision in Latin American countries, Portugal, Italy and Hungary where they are taught as a single continent; the criterion of a discrete landmass is disregarded if the continuous landmass of Eurasia is classified as two separate continents: Europe and Asia.
Physiographically and South Asia are peninsulas of the Eurasian landmass. However, Europe is considered a continent with its comparatively large land area of 10,180,000 square kilometres, while South Asia, with less than half that area, is considered a subcontinent; the alternative view—in geology and geography—that Eurasia is a single continent results in a six-continent view of the world. Some view separation of Eurasia into Asia and Europe as a residue of Eurocentrism: "In physical and historical diversity and India are comparable to the entire European landmass, not to a single European country.." However, for historical and cultural reasons, the view of Europe as a separate continent continues in several categorizations. If continents are defined as discrete landmasses, embracing all the contiguous land of a body Africa and Europe form a single continent which may be referred to as Afro-Eurasia; this produces a four-continent model consisting of Afro-Eurasia, America and Australia. When sea levels were lower during the Pleistocene ice ages, gre
Gravity, or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars and light—are brought toward one another. On Earth, gravity gives weight to physical objects, the Moon's gravity causes the ocean tides; the gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing, forming stars – and for the stars to group together into galaxies – so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become weaker on farther objects. Gravity is most described by the general theory of relativity which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass; the most extreme example of this curvature of spacetime is a black hole, from which nothing—not light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force which causes any two bodies to be attracted to each other, with the force proportional to the product of their masses and inversely proportional to the square of the distance between them.
Gravity is the weakest of the four fundamental forces of physics 1038 times weaker than the strong force, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, it has no significant influence at the level of subatomic particles. In contrast, it is the dominant force at the macroscopic scale, is the cause of the formation and trajectory of astronomical bodies. For example, gravity causes the Earth and the other planets to orbit the Sun, it causes the Moon to orbit the Earth, causes the formation of tides, the formation and evolution of the Solar System and galaxies; the earliest instance of gravity in the Universe in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a unknown manner. Attempts to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework with the other three forces of physics, are a current area of research.
Archimedes discovered the center of gravity of a triangle. He postulated that if the centers of gravity of two equal weights wasn't the same, it would be located in the middle of the line that joins them; the Roman architect and engineer Vitruvius in De Architectura postulated that gravity of an object didn't depend on weight but its "nature". Aryabhata first identified the force to explain why objects are not thrown out when the earth rotates. Brahmagupta described gravity as an attractive force and used the term "gruhtvaakarshan" for gravity. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and early 17th centuries. In his famous experiment dropping balls from the Tower of Pisa, with careful measurements of balls rolling down inclines, Galileo showed that gravitational acceleration is the same for all objects; this was a major departure from Aristotle's belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass fall more in an atmosphere.
Galileo's work set the stage for the formulation of Newton's theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. In his own words, "I deduced that the forces which keep the planets in their orbs must reciprocally as the squares of their distances from the centers about which they revolve: and thereby compared the force requisite to keep the Moon in her Orb with the force of gravity at the surface of the Earth; the equation is the following: F = G m 1 m 2 r 2 Where F is the force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant. Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the general position of the planet, Le Verrier's calculations are what led Johann Gottfried Galle to the discovery of Neptune.
A discrepancy in Mercury's orbit pointed out flaws in Newton's theory. By the end of the 19th century, it was known that its orbit showed slight perturbations that could not be accounted for under Newton's theory, but all searches for another perturbing body had been fruitless; the issue was resolved in 1915 by Albert Einstein's new theory of general relativity, which accounted for the small discrepancy in Mercury's orbit. This discrepancy was the advance in the perihelion of Mercury of 42.98 arcseconds per century. Although Newton's theory has been superseded by Einstein's general relativity, most modern non-relativistic gravitational calculations are still made using Newton
A mountain is a large landform that rises above the surrounding land in a limited area in the form of a peak. A mountain is steeper than a hill. Mountains are formed through tectonic forces or volcanism; these forces can locally raise the surface of the earth. Mountains erode through the action of rivers, weather conditions, glaciers. A few mountains are isolated summits. High elevations on mountains produce colder climates than at sea level; these colder climates affect the ecosystems of mountains: different elevations have different plants and animals. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation, such as mountain climbing; the highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m above mean sea level. The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m. There is no universally accepted definition of a mountain.
Elevation, relief, steepness and continuity have been used as criteria for defining a mountain. In the Oxford English Dictionary a mountain is defined as "a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which to the adjacent elevation, is impressive or notable."Whether a landform is called a mountain may depend on local usage. Mount Scott outside Lawton, Oklahoma, USA, is only 251 m from its base to its highest point. Whittow's Dictionary of Physical Geography states "Some authorities regard eminences above 600 metres as mountains, those below being referred to as hills." In the United Kingdom and the Republic of Ireland, a mountain is defined as any summit at least 2,000 feet high, whilst the official UK government's definition of a mountain, for the purposes of access, is a summit of 600 metres or higher. In addition, some definitions include a topographical prominence requirement 100 or 500 feet. At one time the U.
S. Board on Geographic Names defined a mountain as being 1,000 feet or taller, but has abandoned the definition since the 1970s. Any similar landform lower. However, the United States Geological Survey concludes that these terms do not have technical definitions in the US; the UN Environmental Programme's definition of "mountainous environment" includes any of the following: Elevation of at least 2,500 m. Using these definitions, mountains cover 33% of Eurasia, 19% of South America, 24% of North America, 14% of Africa; as a whole, 24% of the Earth's land mass is mountainous. There are three main types of mountains: volcanic and block. All three types are formed from plate tectonics: when portions of the Earth's crust move and dive. Compressional forces, isostatic uplift and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features; the height of the feature makes it either a hill or, if steeper, a mountain. Major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity.
Volcanoes are formed when a plate is pushed at a mid-ocean ridge or hotspot. At a depth of around 100 km, melting occurs in rock above the slab, forms magma that reaches the surface; when the magma reaches the surface, it builds a volcanic mountain, such as a shield volcano or a stratovolcano. Examples of volcanoes include Mount Pinatubo in the Philippines; the magma does not have to reach the surface in order to create a mountain: magma that solidifies below ground can still form dome mountains, such as Navajo Mountain in the US. Fold mountains occur when two plates collide: shortening occurs along thrust faults and the crust is overthickened. Since the less dense continental crust "floats" on the denser mantle rocks beneath, the weight of any crustal material forced upward to form hills, plateaus or mountains must be balanced by the buoyancy force of a much greater volume forced downward into the mantle, thus the continental crust is much thicker under mountains, compared to lower lying areas.
Rock can fold either asymmetrically. The upfolds are anticlines and the downfolds are synclines: in asymmetric folding there may be recumbent and overturned folds; the Balkan Mountains and the Jura Mountains are examples of fold mountains. Block mountains are caused by faults in the crust: a plane; when rocks on one side of a fault rise relative to the other, it can form a mountain. The uplifted blocks are block horsts; the intervening dropped blocks are termed graben: these can be small or form extensive rift valley systems. This form of landscape can be seen in East Africa, the Vosges, the Basin and Range Province of Western North America and the Rhine valley; these areas occur when the regional stress is extensional and the crust is thinned. During and following uplift, mountains are subjected to the agents of erosion which wear the uplifted area down. Erosion causes the surface of mountains to be younger than the rocks that form the mountains themselves. Glacial processes produce characteristic landforms, such as pyramidal peaks, knife-edge arêtes, bowl-shaped cirques that can contai
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
Volcanism is the phenomenon of eruption of molten rock onto the surface of the Earth or a solid-surface planet or moon, where lava and volcanic gases erupt through a break in the surface called a vent. It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface. Magma from the mantle or lower crust rises through its crust towards the surface. If magma reaches the surface, its behavior depends on the viscosity of the molten constituent rock. Viscous magma produces volcanoes characterised by explosive eruptions, while non-viscous magma produce volcanoes characterised by effusive eruptions pouring large amounts of lava onto the surface. In some cases, rising magma can solidify without reaching the surface. Instead, the cooled and solidified igneous mass crystallises within the crust to form an igneous intrusion; as magma cools the chemicals in the crystals formed are removed from the main mix of the magma, so the chemical content of the remaining magma evolves as it solidifies slowly.
Fresh unevolved magma injections can remobilise more evolved magmas, allowing eruptions from more viscous magmas. Movement of molten rock in the mantle, caused by thermal convection currents, coupled with gravitational effects of changes on the earth's surface drive plate tectonic motion and volcanism. Volcanoes are places; the type of volcano depends on the consistency of the magma. These are formed where magma pushes between existing rock, intrusions can be in the form of batholiths, dikes and layered intrusions. Earthquakes are associated with plate tectonic activity, but some earthquakes are generated as a result of volcanic activity; these are formed. These include geysers, fumaroles and mudpots, they are used as a source of geothermal energy; the amount of gas and ash emitted by volcanic eruptions has a significant effect on the Earth's climate. Large eruptions correlate well with some significant climate change events; when magma cools it forms rocks. The type of rock formed depends on the chemical composition of the magma and how it cools.
Magma that reaches the surface to become lava cools resulting in rocks with small crystals such as basalt. Some of this magma may cool rapidly and will form volcanic glass such as obsidian. Magma trapped below ground in thin intrusions cools more than exposed magma and produces rocks with medium-sized crystals. Magma that remains trapped in large quantities below ground cools most resulting in rocks with larger crystals, such as granite and gabbro. Existing rocks that come into contact with magma may be assimilated into the magma. Other rocks adjacent to the magma may be altered by contact metamorphism or metasomatism as they are affected by the heat and escaping or externally-circulating hydrothermal fluids. Volcanism is not confined only to Earth, but is thought to be found on any body having a solid crust and fluid mantle. Evidence of volcanism should still be found on any body that has had volcanism at some point in its history. Volcanoes have indeed been observed on other bodies in the Solar System – on some, such as Mars, in the shape of mountains that are unmistakably old volcanoes, but on Io actual ongoing eruptions have been observed.
It can be surmised that volcanism exists on planets and moons of this type in other planetary systems as well. In 2014, scientists found 70 lava flows. Bimodal volcanism Continental drift Hotspot Volcanic arc "Glossary of Volcanic Terms". G. J. Hudak, University of Wisconsin Oshkosh, 2001. Retrieved 2010-05-07. Crumpler, L. S. and Lucas, S. G.. "Volcanoes of New Mexico: An Abbreviated Guide For Non-Specialists". Volcanology in New Mexico. New Mexico Museum of Natural History and Science Bulletin. 18: 5–15. Archived from the original on 2007-03-21. Retrieved 2010-04-28. CS1 maint: Uses authors parameter