149-666: The Koro Sea or Sea of Koro is a sea in the Pacific Ocean between Viti Levu island, Fiji to the west and the Lau Islands to the east, surrounded by the islands of the Fijian archipelago. It is named after Koro Island . This article about a geographical location in Fiji is a stub . You can help Misplaced Pages by expanding it . Sea A sea is a large body of salt water . There are particular seas and
298-517: A biodiverse range of larger and smaller animal life. Light is only able to penetrate the top 200 metres (660 ft) so this is the only part of the sea where plants can grow. The surface layers are often deficient in biologically active nitrogen compounds. The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen , its assimilation, nitrification , anammox and denitrification. Some of these processes take place in deep water so that where there
447-683: A mediterranean sea ) or wholly (as inland seas ) enclosed by land . However, an exception to this is the Sargasso Sea which has no coastline and lies within a circular current, the North Atlantic Gyre . Seas are generally larger than lakes and contain salt water, but the Sea of Galilee is a freshwater lake . The United Nations Convention on the Law of the Sea states that all of the ocean
596-409: A meteor and forms a fireball , also known as a shooting star; astronomers call the brightest examples " bolides ". Once it settles on the larger body's surface, the meteor becomes a meteorite. Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create an impact crater . Meteorites that are recovered after being observed as they transit the atmosphere and impact
745-573: A 61-kilogram (135 lb) iron meteorite was found in a Sinagua (c. 1100–1200 AD) burial cyst near Camp Verde, Arizona , respectfully wrapped in a feather cloth. A small pallasite was found in a pottery jar in an old burial found at Pojoaque Pueblo , New Mexico. Nininger reports several other such instances, in the Southwest US and elsewhere, such as the discovery of Native American beads of meteoric iron found in Hopewell burial mounds , and
894-672: A blend of rock and metal, the stony-iron meteorites . Modern classification of meteorites is complex. The review paper of Krot et al. (2007) summarizes modern meteorite taxonomy. About 86% of the meteorites are chondrites, which are named for the small, round particles they contain. These particles, or chondrules , are composed mostly of silicate minerals that appear to have been melted while they were free-floating objects in space. Certain types of chondrites also contain small amounts of organic matter , including amino acids , and presolar grains . Chondrites are typically about 4.55 billion years old and are thought to represent material from
1043-422: A channel in the seabed. It may occur at a gap in a sandbar or near a man-made structure such as a groyne . These strong currents can have a velocity of 3 ft (0.9 m) per second, can form at different places at different stages of the tide and can carry away unwary bathers. Temporary upwelling currents occur when the wind pushes water away from the land and deeper water rises to replace it. This cold water
1192-458: A few centimeters in size that were formed—according to most scientists—by the impacts of large meteorites on Earth's surface. A few researchers have favored tektites originating from the Moon as volcanic ejecta, but this theory has lost much of its support over the last few decades. The diameter of the largest impactor to hit Earth on any given day is likely to be about 40 centimeters (16 inches), in
1341-798: A flat, desert plain about 100 kilometres (62 mi) southeast of Dirj (Daraj), Libya . A few years later, a desert enthusiast saw photographs of meteorites being recovered by scientists in Antarctica, and thought that he had seen similar occurrences in northern Africa . In 1989, he recovered about 100 meteorites from several distinct locations in Libya and Algeria. Over the next several years, he and others who followed found at least 400 more meteorites. The find locations were generally in regions known as regs or hamadas : flat, featureless areas covered only by small pebbles and minor amounts of sand. Dark-colored meteorites can be easily spotted in these places. In
1490-435: A given year about four metres (13 ft), and in a given century about 20 m (66 ft). These statistics are obtained by the following: Over at least the range from five centimeters (2.0 inches) to roughly 300 meters (980 feet), the rate at which Earth receives meteors obeys a power-law distribution as follows: where N (> D ) is the expected number of objects larger than a diameter of D meters to hit Earth in
1639-400: A height of less than three feet, so they often pass unnoticed at this stage. In contrast, ocean surface waves caused by winds have wavelengths of a few hundred feet, travel at up to 65 miles per hour (105 km/h) and are up to 45 feet (14 metres) high. As a tsunami moves into shallower water its speed decreases, its wavelength shortens and its amplitude increases enormously, behaving in
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#17327798780431788-507: A large and multidisciplinary field: it examines the properties of seawater ; studies waves , tides , and currents ; charts coastlines and maps the seabeds ; and studies marine life . The subfield dealing with the sea's motion, its forces, and the forces acting upon it is known as physical oceanography . Marine biology (biological oceanography) studies the plants , animals , and other organisms inhabiting marine ecosystems . Both are informed by chemical oceanography , which studies
1937-453: A low-pressure system, can raise the surface of the sea at high tide dramatically. The Earth is composed of a magnetic central core , a mostly liquid mantle and a hard rigid outer shell (or lithosphere ), which is composed of the Earth's rocky crust and the deeper mostly solid outer layer of the mantle. On land the crust is known as the continental crust while under the sea it is known as
2086-401: A meteorite shower falls is known as its strewn field . Strewn fields are commonly elliptical in shape, with the major axis parallel to the direction of flight. In most cases, the largest meteorites in a shower are found farthest down-range in the strewn field. Most meteorites are stony meteorites, classed as chondrites and achondrites . Only about 6% of meteorites are iron meteorites or
2235-504: A meteorite that was understood by contemporaries to have fallen to the earth from Jupiter , the principal Roman deity. There are reports that a sacred stone was enshrined at the temple that may have been a meteorite. The Black Stone set into the wall of the Kaaba has often been presumed to be a meteorite, but the little available evidence for this is inconclusive. Some Native Americans treated meteorites as ceremonial objects. In 1915,
2384-534: A new world of creatures living on the seabed that scientists had not previously known to exist. Some like the detrivores rely on organic material falling to the ocean floor. Others cluster round deep sea hydrothermal vents where mineral-rich flows of water emerge from the seabed, supporting communities whose primary producers are sulphide-oxidising chemoautotrophic bacteria, and whose consumers include specialised bivalves, sea anemones, barnacles, crabs, worms and fish, often found nowhere else. A dead whale sinking to
2533-512: A radius of a hundred or more kilometers. Whistling and hissing sounds are also sometimes heard but are poorly understood. Following the passage of the fireball, it is not unusual for a dust trail to linger in the atmosphere for several minutes. As meteoroids are heated during atmospheric entry , their surfaces melt and experience ablation . They can be sculpted into various shapes during this process, sometimes resulting in shallow thumbprint-like indentations on their surfaces called regmaglypts . If
2682-554: A rapid rise in commercial collection of meteorites. This process was accelerated when, in 1997, meteorites coming from both the Moon and Mars were found in Libya. By the late 1990s, private meteorite-collecting expeditions had been launched throughout the Sahara. Specimens of the meteorites recovered in this way are still deposited in research collections, but most of the material is sold to private collectors. These expeditions have now brought
2831-536: A saline body of water and therefore solely a sea in the sense of the common use of the word, like all other saltwater lakes called sea. Earth is the only known planet with seas of liquid water on its surface, although Mars possesses ice caps and similar planets in other solar systems may have oceans. Earth's 1,335,000,000 cubic kilometers (320,000,000 cu mi) of sea contain about 97.2 percent of its known water and covers approximately 71 percent of its surface. Another 2.15% of Earth's water
2980-428: A single person, Ivan Wilson. In total, nearly 140 meteorites were found in the region since 1967. In the area of the finds, the ground was originally covered by a shallow, loose soil sitting atop a hardpan layer. During the dustbowl era, the loose soil was blown off, leaving any rocks and meteorites that were present stranded on the exposed surface. Beginning in the mid-1960s, amateur meteorite hunters began scouring
3129-471: A very high range in bays or estuaries . Submarine earthquakes arising from tectonic plate movements under the oceans can lead to destructive tsunamis , as can volcanoes, huge landslides , or the impact of large meteorites . The seas have been an integral element for humans throughout history and culture. Humans harnessing and studying the seas have been recorded since ancient times and evidenced well into prehistory , while its modern scientific study
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#17327798780433278-414: A wide array of species including corals (only six of which contribute to reef formation). Marine primary producers – plants and microscopic organisms in the plankton – are widespread and very essential for the ecosystem. It has been estimated that half of the world's oxygen is produced by phytoplankton. About 45 percent of the sea's primary production of living material
3427-608: A year. This is based on observations of bright meteors seen from the ground and space, combined with surveys of near-Earth asteroids . Above 300 m (980 ft) in diameter, the predicted rate is somewhat higher, with a 2 km (1.2 mi) asteroid (one teraton TNT equivalent ) every couple of million years – about 10 times as often as the power-law extrapolation would predict. In 2015, NASA scientists reported that complex organic compounds found in DNA and RNA , including uracil , cytosine , and thymine , have been formed in
3576-529: Is "sea". The law of the sea has at its center the definition of the boundaries of the ocean, clarifying its application in marginal seas . But what bodies of water other than the sea the law applies to is being crucially negotiated in the case of the Caspian Sea and its status as "sea", basically revolving around the issue of the Caspian Sea about either being factually an oceanic sea or only
3725-456: Is 0.4%. Stony-iron meteorites constitute the remaining 1%. They are a mixture of iron-nickel metal and silicate minerals. One type, called pallasites , is thought to have originated in the boundary zone above the core regions where iron meteorites originated. The other major type of stony-iron meteorites is the mesosiderites . Tektites (from Greek tektos , molten) are not themselves meteorites, but are rather natural glass objects up to
3874-449: Is a continuous circulation of water in the oceans. Warm surface currents cool as they move away from the tropics, and the water becomes denser and sinks. The cold water moves back towards the equator as a deep sea current, driven by changes in the temperature and density of the water, before eventually welling up again towards the surface. Deep seawater has a temperature between −2 °C (28 °F) and 5 °C (41 °F) in all parts of
4023-516: Is a meteorite collected after its arrival was observed by people or automated devices. Any other meteorite is called a "meteorite find". There are more than 1,100 documented falls listed in widely used databases, most of which have specimens in modern collections. As of January 2019 , the Meteoritical Bulletin Database had 1,180 confirmed falls. Most meteorite falls are collected on the basis of eyewitness accounts of
4172-399: Is a point of land jutting out into the sea and a larger promontory is known as a cape . The indentation of a coastline, especially between two headlands, is a bay , a small bay with a narrow inlet is a cove and a large bay may be referred to as a gulf . Coastlines are influenced by several factors including the strength of the waves arriving on the shore, the gradient of the land margin,
4321-487: Is an upwelling of cold waters, and also near estuaries where land-sourced nutrients are present, plant growth is higher. This means that the most productive areas, rich in plankton and therefore also in fish, are mainly coastal. There is a broader spectrum of higher animal taxa in the sea than on land, many marine species have yet to be discovered and the number known to science is expanding annually. Some vertebrates such as seabirds , seals and sea turtles return to
4470-556: Is called oceanography and maritime space is governed by the law of the sea , with admiralty law regulating human interactions at sea. The seas provide substantial supplies of food for humans, mainly fish , but also shellfish , mammals and seaweed , whether caught by fishermen or farmed underwater. Other human uses of the seas include trade , travel, mineral extraction , power generation , warfare , and leisure activities such as swimming , sailing , and scuba diving . Many of these activities create marine pollution . The sea
4619-478: Is contributed by diatoms . Much larger algae, commonly known as seaweeds , are important locally; Sargassum forms floating drifts, while kelp form seabed forests. Flowering plants in the form of seagrasses grow in " meadows " in sandy shallows, mangroves line the coast in tropical and subtropical regions and salt-tolerant plants thrive in regularly inundated salt marshes . All of these habitats are able to sequester large quantities of carbon and support
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4768-413: Is currently prohibited by national law, but a number of international hunters continue to remove specimens now deemed national treasures. This new law provoked a small international incident , as its implementation preceded any public notification of such a law, resulting in the prolonged imprisonment of a large group of meteorite hunters, primarily from Russia, but whose party also consisted of members from
4917-481: Is frozen, found in the sea ice covering the Arctic Ocean , the ice cap covering Antarctica and its adjacent seas , and various glaciers and surface deposits around the world. The remainder (about 0.65% of the whole) form underground reservoirs or various stages of the water cycle , containing the freshwater encountered and used by most terrestrial life : vapor in the air , the clouds it slowly forms,
5066-401: Is likely to reduce levels of oxygen in surface waters since the solubility of oxygen in water falls at higher temperatures. Ocean deoxygenation is projected to increase hypoxia by 10%, and triple suboxic waters (oxygen concentrations 98% less than the mean surface concentrations), for each 1 °C of upper-ocean warming. The amount of light that penetrates the sea depends on the angle of
5215-530: Is near the Mariana Islands , a volcanic archipelago in the West Pacific. Its deepest point is 10.994 kilometres (nearly 7 miles) below the surface of the sea. The zone where land meets sea is known as the coast and the part between the lowest spring tides and the upper limit reached by splashing waves is the shore . A beach is the accumulation of sand or shingle on the shore. A headland
5364-490: Is often rich in nutrients and creates blooms of phytoplankton and a great increase in the productivity of the sea. Tides are the regular rise and fall in water level experienced by seas and oceans in response to the gravitational influences of the Moon and the Sun, and the effects of the Earth's rotation. During each tidal cycle, at any given place the water rises to a maximum height known as "high tide" before ebbing away again to
5513-595: Is the interconnected system of all the Earth's oceanic waters, including the Atlantic , Pacific , Indian , Southern and Arctic Oceans . However, the word "sea" can also be used for many specific, much smaller bodies of seawater, such as the North Sea or the Red Sea . There is no sharp distinction between seas and oceans , though generally seas are smaller, and are often partly (as marginal seas or particularly as
5662-419: Is turned into kinetic energy, creating a shallow wave, a tsunami, radiating outwards at a velocity proportional to the square root of the depth of the water and which therefore travels much faster in the open ocean than on a continental shelf. In the deep open sea, tsunamis have wavelengths of around 80 to 300 miles (130 to 480 km), travel at speeds of over 600 miles per hour (970 km/h) and usually have
5811-651: The Coriolis effect . The surface currents flow in a clockwise direction in the Northern Hemisphere and anticlockwise in the Southern Hemisphere. The water moving away from the equator is warm, and that flowing in the reverse direction has lost most of its heat. These currents tend to moderate the Earth's climate, cooling the equatorial region and warming regions at higher latitudes. Global climate and weather forecasts are powerfully affected by
5960-613: The Dhofar and Al Wusta regions of Oman, south of the sandy deserts of the Rub' al Khali , had yielded about 5,000 meteorites as of mid-2009. Included among these are a large number of lunar and Martian meteorites, making Oman a particularly important area both for scientists and collectors. Early expeditions to Oman were mainly done by commercial meteorite dealers, however, international teams of Omani and European scientists have also now collected specimens. The recovery of meteorites from Oman
6109-857: The Mediterranean and Red Sea with the Egyptian Hannu reaching the Arabian Peninsula and the African Coast around 2750 BC. In the first millennium BC, Phoenicians and Greeks established colonies throughout the Mediterranean and the Black Sea . Around 500 BC, the Carthaginian navigator Hanno left a detailed periplus of an Atlantic journey that reached at least Senegal and possibly Mount Cameroon . In
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6258-699: The asteroid belt that never coalesced into large bodies. Like comets , chondritic asteroids are some of the oldest and most primitive materials in the Solar System . Chondrites are often considered to be "the building blocks of the planets". About 8% of the meteorites are achondrites (meaning they do not contain chondrules), some of which are similar to terrestrial igneous rocks . Most achondrites are also ancient rocks, and are thought to represent crustal material of differentiated planetesimals. One large family of achondrites (the HED meteorites ) may have originated on
6407-584: The early Mediaeval period , the Vikings crossed the North Atlantic and even reached the northeastern fringes of North America. Novgorodians had also been sailing the White Sea since the 13th century or before. Meanwhile, the seas along the eastern and southern Asian coast were used by Arab and Chinese traders. The Chinese Ming Dynasty had a fleet of 317 ships with 37,000 men under Zheng He in
6556-422: The genetic code of all life on Earth. These compounds have also occurred spontaneously in laboratory settings emulating conditions in outer space. Until recently, the source of only about 6% of meteorites had been traced to their sources: the Moon, Mars, and asteroid Vesta. Approximately 70% of meteorites found on Earth now appear to originate from break-ups of three asteroids. Most meteorites date from
6705-614: The hundred-year wave ) they are designed against. Rogue waves, however, have been documented at heights above 25 meters (82 ft). The top of a wave is known as the crest, the lowest point between waves is the trough and the distance between the crests is the wavelength. The wave is pushed across the surface of the sea by the wind, but this represents a transfer of energy and not a horizontal movement of water. As waves approach land and move into shallow water , they change their behavior. If approaching at an angle, waves may bend ( refraction ) or wrap rocks and headlands ( diffraction ). When
6854-422: The oceanic crust . The latter is composed of relatively dense basalt and is some five to ten kilometres (three to six miles) thick. The relatively thin lithosphere floats on the weaker and hotter mantle below and is fractured into a number of tectonic plates . In mid-ocean, magma is constantly being thrust through the seabed between adjoining plates to form mid-oceanic ridges and here convection currents within
7003-436: The photosynthetic activity of these plants produces oxygen, which dissolves in the seawater and is used by marine animals. At night, photosynthesis stops, and the amount of dissolved oxygen declines. In the deep sea, where insufficient light penetrates for plants to grow, there is very little dissolved oxygen. In its absence, organic material is broken down by anaerobic bacteria producing hydrogen sulphide . Climate change
7152-421: The rain falling from them, and the lakes and rivers spontaneously formed as its waters flow again and again to the sea. The scientific study of water and Earth's water cycle is hydrology ; hydrodynamics studies the physics of water in motion. The more recent study of the sea in particular is oceanography . This began as the study of the shape of the ocean's currents but has since expanded into
7301-416: The same source , a collision that occurred somewhere between Jupiter and Mars. One of these fossil meteorites, dubbed Österplana 065 , appears to represent a distinct type of meteorite that is "extinct" in the sense that it is no longer falling to Earth, the parent body having already been completely depleted from the reservoir of near-Earth objects . A "meteorite fall", also called an "observed fall",
7450-412: The swash moves beach material seawards. Under their influence, the sand and shingle on the beach is ground together and abraded. Around high tide, the power of a storm wave impacting on the foot of a cliff has a shattering effect as air in cracks and crevices is compressed and then expands rapidly with release of pressure. At the same time, sand and pebbles have an erosive effect as they are thrown against
7599-420: The water , carbon , and nitrogen cycles . The surface of water interacts with the atmosphere, exchanging properties such as particles and temperature, as well as currents . Surface currents are the water currents that are produced by the atmosphere's currents and its winds blowing over the surface of the water, producing wind waves , setting up through drag slow but stable circulations of water, as in
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#17327798780437748-530: The 10th Japanese Antarctic Research Expedition found nine meteorites on a blue ice field near the Yamato Mountains . With this discovery, came the realization that movement of ice sheets might act to concentrate meteorites in certain areas. After a dozen other specimens were found in the same place in 1973, a Japanese expedition was launched in 1974 dedicated to the search for meteorites. This team recovered nearly 700 meteorites. Shortly thereafter,
7897-737: The American Southwest have been submitted with false find locations, as many finders think it is unwise to publicly share that information for fear of confiscation by the federal government and competition with other hunters at published find sites. Several of the meteorites found recently are currently on display in the Griffith Observatory in Los Angeles, and at UCLA 's Meteorite Gallery. A few meteorites were found in Antarctica between 1912 and 1964. In 1969,
8046-569: The Austronesian " Lapita " peoples displayed great feats of navigation, reaching out from the Bismarck Archipelago to as far away as Fiji , Tonga , and Samoa . Their descendants continued to travel thousands of miles between tiny islands on outrigger canoes , and in the process they found many new islands, including Hawaii , Easter Island (Rapa Nui), and New Zealand. The Ancient Egyptians and Phoenicians explored
8195-694: The Earth are called meteorite falls . All others are known as meteorite finds . Meteorites have traditionally been divided into three broad categories: stony meteorites that are rocks, mainly composed of silicate minerals ; iron meteorites that are largely composed of ferronickel ; and stony-iron meteorites that contain large amounts of both metallic and rocky material. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition and mineralogy. "Meteorites" less than ~1 mm in diameter are classified as micrometeorites , however micrometeorites differ from meteorites in that they typically melt completely in
8344-405: The Earth , clarified the process of sedimentation , and assisted the study of volcanism and earthquakes . A characteristic of seawater is that it is salty. Salinity is usually measured in parts per thousand ( ‰ or per mil), and the open ocean has about 35 grams (1.2 oz) solids per litre, a salinity of 35 ‰. The Mediterranean Sea is slightly higher at 38 ‰, while the salinity of
8493-452: The Earth are caused by iron meteoroids, which are most easily able to transit the atmosphere intact. Examples of craters caused by iron meteoroids include Barringer Meteor Crater , Odessa Meteor Crater , Wabar craters , and Wolfe Creek crater ; iron meteorites are found in association with all of these craters. In contrast, even relatively large stony or icy bodies such as small comets or asteroids , up to millions of tons, are disrupted in
8642-420: The Earth is closest to the Moon because it is also where the effect of the Moon's gravity is stronger. On the opposite side of the Earth, the lunar force is at its weakest and this causes another bulge to form. As the Moon rotates around the Earth, so do these ocean bulges move around the Earth. The gravitational attraction of the Sun is also working on the seas, but its effect on tides is less powerful than that of
8791-411: The Earth to make a complete revolution and return the Moon to its previous position relative to an observer. The Moon's mass is some 27 million times smaller than the Sun, but it is 400 times closer to the Earth. Tidal force or tide-raising force decreases rapidly with distance, so the moon has more than twice as great an effect on tides as the Sun. A bulge is formed in the ocean at the place where
8940-624: The Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, Innisfree , in 1977. Finally, observations by the European Fireball Network , a descendant of the original Czech program that recovered Příbram, led to the discovery and orbit calculations for the Neuschwanstein meteorite in 2002. NASA has an automated system that detects meteors and calculates
9089-413: The Moon, and when the Sun, Moon and Earth are all aligned (full moon and new moon), the combined effect results in the high "spring tides". In contrast, when the Sun is at 90° from the Moon as viewed from Earth, the combined gravitational effect on tides is less causing the lower "neap tides". A storm surge can occur when high winds pile water up against the coast in a shallow area and this, coupled with
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#17327798780439238-721: The Příbram fall, other nations established automated observing programs aimed at studying infalling meteorites. One of these was the Prairie Network , operated by the Smithsonian Astrophysical Observatory from 1963 to 1975 in the midwestern US . This program also observed a meteorite fall, the Lost City chondrite, allowing its recovery and a calculation of its orbit. Another program in Canada,
9387-556: The Southern Hemisphere in the Roaring Forties , long, organised masses of water called swell roll across the ocean. If the wind dies down, the wave formation is reduced, but already-formed waves continue to travel in their original direction until they meet land. The size of the waves depends on the fetch , the distance that the wind has blown over the water and the strength and duration of that wind. When waves meet others coming from different directions, interference between
9536-505: The Spanish Magellan-Elcano expedition which would be the first to sail around the world. Meteorite A meteorite is a rock that originated in outer space and has fallen to the surface of a planet or moon . When the original object enters the atmosphere, various factors such as friction , pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate energy. It then becomes
9685-469: The US as well as several other European countries. Meteorites have figured into human culture since their earliest discovery as ceremonial or religious objects, as the subject of writing about events occurring in the sky and as a source of peril. The oldest known iron artifacts are nine small beads hammered from meteoritic iron. They were found in northern Egypt and have been securely dated to 3200 BC. Although
9834-931: The United States began its own program to search for Antarctic meteorites, operating along the Transantarctic Mountains on the other side of the continent: the Antarctic Search for Meteorites ( ANSMET ) program. European teams, starting with a consortium called "EUROMET" in the 1990/91 season, and continuing with a program by the Italian Programma Nazionale di Ricerche in Antartide have also conducted systematic searches for Antarctic meteorites. The Antarctic Scientific Exploration of China has conducted successful meteorite searches since 2000. A Korean program (KOREAMET)
9983-517: The added CO 2 is absorbed by the oceans, forming carbonic acid and lowering the pH (now below 8.1 ) through a process called ocean acidification . The extent of further ocean chemistry changes, including ocean pH, will depend on climate change mitigation efforts taken by nations and their governments. The amount of oxygen found in seawater depends primarily on the plants growing in it. These are mainly algae, including phytoplankton , with some vascular plants such as seagrasses . In daylight,
10132-754: The arid areas of the southwestern United States. To date, thousands of meteorites have been recovered from the Mojave , Sonoran , Great Basin , and Chihuahuan Deserts , with many being recovered on dry lake beds. Significant finds include the three-tonne Old Woman meteorite , currently on display at the Desert Discovery Center in Barstow, California , and the Franconia and Gold Basin meteorite strewn fields; hundreds of kilograms of meteorites have been recovered from each. A number of finds from
10281-406: The atmosphere and fall to Earth as quenched droplets. Extraterrestrial meteorites have been found on the Moon and on Mars. Most meteoroids disintegrate when entering the Earth's atmosphere. Usually, five to ten a year are observed to fall and are subsequently recovered and made known to scientists. Few meteorites are large enough to create large impact craters . Instead, they typically arrive at
10430-516: The atmosphere can appear to be very bright, rivaling the sun in intensity, although most are far dimmer and may not even be noticed during the daytime. Various colors have been reported, including yellow, green, and red. Flashes and bursts of light can occur as the object breaks up. Explosions, detonations, and rumblings are often heard during meteorite falls, which can be caused by sonic booms as well as shock waves resulting from major fragmentation events. These sounds can be heard over wide areas, with
10579-433: The atmosphere, and do not make impact craters. Although such disruption events are uncommon, they can cause a considerable concussion to occur; the famed Tunguska event probably resulted from such an incident. Very large stony objects, hundreds of meters in diameter or more, weighing tens of millions of tons or more, can reach the surface and cause large craters but are very rare. Such events are generally so energetic that
10728-411: The behavior of elements and molecules within the oceans: particularly, at the moment, the ocean's role in the carbon cycle and carbon dioxide 's role in the increasing acidification of seawater. Marine and maritime geography charts the shape and shaping of the sea, while marine geology (geological oceanography) has provided evidence of continental drift and the composition and structure of
10877-529: The bottom of the ocean provides food for an assembly of organisms which similarly rely largely on the actions of sulphur-reducing bacteria. Such places support unique biomes where many new microbes and other lifeforms have been discovered. Humans have travelled the seas since they first built sea-going craft. Mesopotamians were using bitumen to caulk their reed boats and, a little later, masted sails . By c. 3000 BC, Austronesians on Taiwan had begun spreading into maritime Southeast Asia . Subsequently,
11026-467: The boundaries between the land and sea, the slightly denser oceanic plates slide beneath the continental plates and more subduction trenches are formed. As they grate together, the continental plates are deformed and buckle causing mountain building and seismic activity. The Earth's deepest trench is the Mariana Trench which extends for about 2,500 kilometres (1,600 miles) across the seabed. It
11175-780: The case of several meteorite fields, such as Dar al Gani , Dhofar, and others, favorable light-colored geology consisting of basic rocks (clays, dolomites , and limestones ) makes meteorites particularly easy to identify. Although meteorites had been sold commercially and collected by hobbyists for many decades, up to the time of the Saharan finds of the late 1980s and early 1990s, most meteorites were deposited in or purchased by museums and similar institutions where they were exhibited and made available for scientific research . The sudden availability of large numbers of meteorites that could be found with relative ease in places that were readily accessible (especially compared to Antarctica), led to
11324-466: The case of the ocean sustaining deep-sea ocean currents . Deep-sea currents, known together as the global conveyor belt , carry cold water from near the poles to every ocean and significantly influence Earth's climate. Tides , the generally twice-daily rise and fall of sea levels , are caused by Earth's rotation and the gravitational effects of the Moon and, to a lesser extent, of the Sun . Tides may have
11473-437: The coast scour out channels and transport sand and pebbles away from their place of origin. Sediment carried to the sea by rivers settles on the seabed causing deltas to form in estuaries. All these materials move back and forth under the influence of waves, tides and currents. Dredging removes material and deepens channels but may have unexpected effects elsewhere on the coastline. Governments make efforts to prevent flooding of
11622-446: The composition and hardness of the coastal rock, the inclination of the off-shore slope and the changes of the level of the land due to local uplift or submergence. Normally, waves roll towards the shore at the rate of six to eight per minute and these are known as constructive waves as they tend to move material up the beach and have little erosive effect. Storm waves arrive on shore in rapid succession and are known as destructive waves as
11771-598: The continental shelf. Alternatively, marine habitats can be divided vertically into pelagic (open water), demersal (just above the seabed) and benthic (sea bottom) habitats. A third division is by latitude : from polar seas with ice shelves, sea ice and icebergs, to temperate and tropical waters. Coral reefs, the so-called "rainforests of the sea", occupy less than 0.1 percent of the world's ocean surface, yet their ecosystems include 25 percent of all marine species. The best-known are tropical coral reefs such as Australia's Great Barrier Reef , but cold water reefs harbour
11920-399: The course of clearing a field. The result was the discovery of more than 200 new meteorites, mostly stony types. In the late 1960s, Roosevelt County, New Mexico was found to be a particularly good place to find meteorites. After the discovery of a few meteorites in 1967, a public awareness campaign resulted in the finding of nearly 100 new specimens in the next few years, with many being by
12069-522: The currents. Most of the smallest organisms are the larvae of fish and marine invertebrates which liberate eggs in vast numbers because the chance of any one embryo surviving to maturity is so minute. The zooplankton feed on phytoplankton and on each other and form a basic part of the complex food chain that extends through variously sized fish and other nektonic organisms to large squid , sharks , porpoises , dolphins and whales . Some marine creatures make large migrations, either to other regions of
12218-436: The depths of the ocean; however, the relative proportions of dissolved salts vary little across the oceans. The most abundant solid dissolved in seawater is sodium chloride . The water also contains salts of magnesium , calcium , potassium , and mercury , amongst many other elements, some in minute concentrations. A wide variety of organisms , including bacteria , protists , algae , plants, fungi , and animals live in
12367-410: The destruction may be caused by the flood water draining back into the sea after the tsunami has struck, dragging debris and people with it. Often several tsunami are caused by a single geological event and arrive at intervals of between eight minutes and two hours. The first wave to arrive on shore may not be the biggest or most destructive. Wind blowing over the surface of the sea causes friction at
12516-413: The direction of the wind. The friction between air and water caused by a gentle breeze on a pond causes ripples to form. A strong blow over the ocean causes larger waves as the moving air pushes against the raised ridges of water. The waves reach their maximum height when the rate at which they are travelling nearly matches the speed of the wind. In open water, when the wind blows continuously as happens in
12665-533: The discovery of the Winona meteorite in a Native American stone-walled crypt. In medieval China during the Song dynasty , a meteorite strike event was recorded by Shen Kuo in 1064 AD near Changzhou . He reported "a loud noise that sounded like a thunder was heard in the sky; a giant star, almost like the moon, appeared in the southeast" and later finding the crater and the still-hot meteorite within, nearby. Two of
12814-534: The early Solar System and are by far the oldest extant material on Earth. Analysis of terrestrial weathering due to water, salt, oxygen, etc. is used to quantify the degree of alteration that a meteorite has experienced. Several qualitative weathering indices have been applied to Antarctic and desertic samples. The most commonly employed weathering scale, used for ordinary chondrites , ranges from W0 (pristine state) to W6 (heavy alteration). "Fossil" meteorites are sometimes discovered by geologists. They represent
12963-571: The early fifteenth century, sailing the Indian and Pacific Oceans. In the late fifteenth century, Western European mariners started making longer voyages of exploration in search of trade. Bartolomeu Dias rounded the Cape of Good Hope in 1487 and Vasco da Gama reached India via the Cape in 1498. Christopher Columbus sailed from Cadiz in 1492, attempting to reach the eastern lands of India and Japan by
13112-450: The extremely arid climate, there has been relatively little weathering or sedimentation on the surface for tens of thousands of years, allowing meteorites to accumulate without being buried or destroyed. The dark-colored meteorites can then be recognized among the very different looking limestone pebbles and rocks. In 1986–87, a German team installing a network of seismic stations while prospecting for oil discovered about 65 meteorites on
13261-424: The fireball or the impact of the object on the ground, or both. Therefore, despite the fact that meteorites fall with virtually equal probability everywhere on Earth, verified meteorite falls tend to be concentrated in areas with higher human population densities such as Europe, Japan, and northern India. A small number of meteorite falls have been observed with automated cameras and recovered following calculation of
13410-457: The first time, including ribose , suggesting that chemical processes on asteroids can produce some organic compounds fundamental to life, and supporting the notion of an RNA world prior to a DNA-based origin of life on Earth. In 2022, a Japanese group reported that they had found adenine (A), thymine (T), guanine (G), cytosine (C) and uracil (U) inside carbon-rich meteorites. These compounds are building blocks of DNA and RNA ,
13559-422: The food chain or precipitated into the deeper, more carbon-rich layers as dead soft tissue or in shells and bones as calcium carbonate . It circulates in this layer for long periods of time before either being deposited as sediment or being returned to surface waters through thermohaline circulation. The oceans are home to a diverse collection of life forms that use it as a habitat. Since sunlight illuminates only
13708-580: The gap and a circular movement of surface currents known as a gyre is formed. There are five main gyres in the world's oceans: two in the Pacific, two in the Atlantic and one in the Indian Ocean. Other smaller gyres are found in lesser seas and a single gyre flows around Antarctica . These gyres have followed the same routes for millennia, guided by the topography of the land, the wind direction and
13857-570: The globe. Seawater with a typical salinity of 35 ‰ has a freezing point of about −1.8 °C (28.8 °F). When its temperature becomes low enough, ice crystals form on the surface. These break into small pieces and coalesce into flat discs that form a thick suspension known as frazil . In calm conditions, this freezes into a thin flat sheet known as nilas , which thickens as new ice forms on its underside. In more turbulent seas, frazil crystals join into flat discs known as pancakes. These slide under each other and coalesce to form floes . In
14006-552: The highly weathered remains of meteorites that fell to Earth in the remote past and were preserved in sedimentary deposits sufficiently well that they can be recognized through mineralogical and geochemical studies. The Thorsberg limestone quarry in Sweden has produced an anomalously large number – exceeding one hundred – fossil meteorites from the Ordovician , nearly all of which are highly weathered L-chondrites that still resemble
14155-456: The hot deserts of Australia . Several dozen meteorites had already been found in the Nullarbor region of Western and South Australia . Systematic searches between about 1971 and the present recovered more than 500 others, ~300 of which are currently well characterized. The meteorites can be found in this region because the land presents a flat, featureless, plain covered by limestone . In
14304-586: The impact point. The first of these was the Příbram meteorite , which fell in Czechoslovakia (now the Czech Republic) in 1959. In this case, two cameras used to photograph meteors captured images of the fireball. The images were used both to determine the location of the stones on the ground and, more significantly, to calculate for the first time an accurate orbit for a recovered meteorite. Following
14453-568: The impactor is completely destroyed, leaving no meteorites. (The first example of a stony meteorite found in association with a large impact crater, the Morokweng impact structure in South Africa, was reported in May 2006.) Several phenomena are well documented during witnessed meteorite falls too small to produce hypervelocity craters. The fireball that occurs as the meteoroid passes through
14602-442: The interface between air and sea. Not only does this cause waves to form, but it also makes the surface seawater move in the same direction as the wind. Although winds are variable, in any one place they predominantly blow from a single direction and thus a surface current can be formed. Westerly winds are most frequent in the mid-latitudes while easterlies dominate the tropics. When water moves in this way, other water flows in to fill
14751-549: The laboratory under outer space conditions, using starting chemicals, such as pyrimidine , found in meteorites. Pyrimidine and polycyclic aromatic hydrocarbons (PAHs) may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists. In 2018, researchers found that 4.5 billion-year-old meteorites found on Earth contained liquid water along with prebiotic complex organic substances that may be ingredients for life. In 2019, scientists reported detecting sugar molecules in meteorites for
14900-484: The land by the building of breakwaters , seawalls , dykes and levees and other sea defences. For instance, the Thames Barrier is designed to protect London from a storm surge, while the failure of the dykes and levees around New Orleans during Hurricane Katrina created a humanitarian crisis in the United States. The sea plays a part in the water or hydrological cycle , in which water evaporates from
15049-523: The land to breed but fish, cetaceans and sea snakes have a completely aquatic lifestyle and many invertebrate phyla are entirely marine. In fact, the oceans teem with life and provide many varying microhabitats. One of these is the surface film which, even though tossed about by the movement of waves, provides a rich environment and is home to bacteria, fungi , microalgae , protozoa , fish eggs and various larvae. The pelagic zone contains macro- and microfauna and myriad zooplankton which drift with
15198-648: The levels of salinity in different seas, the relative composition of the dissolved salts is stable throughout the world's oceans. Seawater is too saline for humans to drink safely, as the kidneys cannot excrete urine as salty as seawater. Although the amount of salt in the ocean remains relatively constant within the scale of millions of years, various factors affect the salinity of a body of water. Evaporation and by-product of ice formation (known as "brine rejection") increase salinity, whereas precipitation , sea ice melt, and runoff from land reduce it. The Baltic Sea , for example, has many rivers flowing into it, and thus
15347-508: The mantle tend to drive the two plates apart. Parallel to these ridges and nearer the coasts, one oceanic plate may slide beneath another oceanic plate in a process known as subduction . Deep trenches are formed here and the process is accompanied by friction as the plates grind together. The movement proceeds in jerks which cause earthquakes, heat is produced and magma is forced up creating underwater mountains, some of which may form chains of volcanic islands near to deep trenches. Near some of
15496-463: The meteoroid maintains a fixed orientation for some time, without tumbling, it may develop a conical "nose cone" or "heat shield" shape. As it decelerates, eventually the molten surface layer solidifies into a thin fusion crust, which on most meteorites is black (on some achondrites , the fusion crust may be very light-colored). On stony meteorites, the heat-affected zone is at most a few mm deep; in iron meteorites, which are more thermally conductive,
15645-416: The minimum "low tide" level. As the water recedes, it uncovers more and more of the foreshore , also known as the intertidal zone. The difference in height between the high tide and low tide is known as the tidal range or tidal amplitude. Most places experience two high tides each day, occurring at intervals of about 12 hours and 25 minutes. This is half the 24 hours and 50 minute period that it takes for
15794-437: The more notable meteorites recovered include Tissint and Northwest Africa 7034 . Tissint was the first witnessed Martian meteorite fall in more than fifty years; NWA 7034 is the oldest meteorite known to come from Mars, and is a unique water-bearing regolith breccia. In 1999, meteorite hunters discovered that the desert in southern and central Oman were also favorable for the collection of many specimens. The gravel plains in
15943-539: The northern Red Sea can reach 41‰. In contrast, some landlocked hypersaline lakes have a much higher salinity, for example, the Dead Sea has 300 grams (11 oz) dissolved solids per litre (300 ‰). While the constituents of table salt ( sodium and chloride ) make up about 85 percent of the solids in solution, there are also other metal ions such as magnesium and calcium , and negative ions including sulphate , carbonate , and bromide . Despite variations in
16092-730: The novel means of travelling westwards. He made landfall instead on an island in the Caribbean Sea and a few years later, the Venetian navigator John Cabot reached Newfoundland . The Italian Amerigo Vespucci , after whom America was named, explored the South American coastline in voyages made between 1497 and 1502, discovering the mouth of the Amazon River . In 1519 the Portuguese navigator Ferdinand Magellan led
16241-484: The ocean depths caused by the movement of deep water masses. A main deep ocean current flows through all the world's oceans and is known as the thermohaline circulation or global conveyor belt. This movement is slow and is driven by differences in density of the water caused by variations in salinity and temperature. At high latitudes the water is chilled by the low atmospheric temperature and becomes saltier as sea ice crystallizes out. Both these factors make it denser, and
16390-440: The ocean on a seasonal basis or vertical migrations daily, often ascending to feed at night and descending to safety by day. Ships can introduce or spread invasive species through the discharge of ballast water or the transport of organisms that have accumulated as part of the fouling community on the hulls of vessels. The demersal zone supports many animals that feed on benthic organisms or seek protection from predators and
16539-471: The ocean, travels through the atmosphere as vapour, condenses , falls as rain or snow , thereby sustaining life on land, and largely returns to the sea. Even in the Atacama Desert , where little rain ever falls, dense clouds of fog known as the camanchaca blow in from the sea and support plant life. In central Asia and other large land masses, there are endorheic basins which have no outlet to
16688-808: The oldest recorded meteorite falls in Europe are the Elbogen (1400) and Ensisheim (1492) meteorites. The German physicist, Ernst Florens Chladni , was the first to publish (in 1794) the idea that meteorites might be rocks that originated not from Earth, but from space. His booklet was "On the Origin of the Iron Masses Found by Pallas and Others Similar to it, and on Some Associated Natural Phenomena" . In this he compiled all available data on several meteorite finds and falls concluded that they must have their origins in outer space. The scientific community of
16837-406: The only materials from other planets ever recovered by humans. About 5% of meteorites that have been seen to fall are iron meteorites composed of iron- nickel alloys , such as kamacite and/or taenite . Most iron meteorites are thought to come from the cores of planetesimals that were once molten. As with the Earth, the denser metal separated from silicate material and sank toward the center of
16986-423: The open pelagic zone. The organisms living in the sea range from whales 30 metres (98 feet) long to microscopic phytoplankton and zooplankton , fungi, and bacteria. Marine life plays an important part in the carbon cycle as photosynthetic organisms convert dissolved carbon dioxide into organic carbon and it is economically important to humans for providing fish for use as food. Life may have originated in
17135-502: The orbit, magnitude, ground track , and other parameters over the southeast USA, which often detects a number of events each night. Until the twentieth century, only a few hundred meteorite finds had ever been discovered. More than 80% of these were iron and stony-iron meteorites, which are easily distinguished from local rocks. To this day, few stony meteorites are reported each year that can be considered to be "accidental" finds. The reason there are now more than 30,000 meteorite finds in
17284-595: The original meteorite under a petrographic microscope , but which have had their original material almost entirely replaced by terrestrial secondary mineralization. The extraterrestrial provenance was demonstrated in part through isotopic analysis of relict spinel grains, a mineral that is common in meteorites, is insoluble in water, and is able to persist chemically unchanged in the terrestrial weathering environment. Scientists believe that these meteorites, which have all also been found in Russia and China, all originated from
17433-487: The parent body of the Vesta Family , although this claim is disputed. Others derive from unidentified asteroids. Two small groups of achondrites are special, as they are younger and do not appear to come from the asteroid belt. One of these groups comes from the Moon, and includes rocks similar to those brought back to Earth by Apollo and Luna programs. The other group is almost certainly from Mars and constitutes
17582-569: The planetesimal, forming its core. After the planetesimal solidified, it broke up in a collision with another planetesimal. Due to the low abundance of iron meteorites in collection areas such as Antarctica, where most of the meteoric material that has fallen can be recovered, it is possible that the percentage of iron-meteorite falls is lower than 5%. This would be explained by a recovery bias; laypeople are more likely to notice and recover solid masses of metal than most other meteorite types. The abundance of iron meteorites relative to total Antarctic finds
17731-430: The process of freezing, salt water and air are trapped between the ice crystals. Nilas may have a salinity of 12–15 ‰, but by the time the sea ice is one year old, this falls to 4–6 ‰. Seawater is slightly alkaline and had an average pH of about 8.2 over the past 300 million years. More recently, climate change has resulted in an increase of the carbon dioxide content of the atmosphere; about 30–40% of
17880-418: The quality of the inflowing water. Oceans contain the greatest quantity of actively cycled carbon in the world and are second only to the lithosphere in the amount of carbon they store. The oceans' surface layer holds large amounts of dissolved organic carbon that is exchanged rapidly with the atmosphere. The deep layer's concentration of dissolved inorganic carbon is about 15 percent higher than that of
18029-417: The rocks. This tends to undercut the cliff, and normal weathering processes such as the action of frost follows, causing further destruction. Gradually, a wave-cut platform develops at the foot of the cliff and this has a protective effect, reducing further wave-erosion. Material worn from the margins of the land eventually ends up in the sea. Here it is subject to attrition as currents flowing parallel to
18178-409: The same way as a wind-generated wave in shallow water but on a vastly greater scale. Either the trough or the crest of a tsunami can arrive at the coast first. In the former case, the sea draws back and leaves subtidal areas close to the shore exposed which provides a useful warning for people on land. When the crest arrives, it does not usually break but rushes inland, flooding all in its path. Much of
18327-530: The sea . The sea commonly refers to the Ocean , the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas , second-order sections of the oceanic sea (e.g. the Mediterranean Sea ), or certain large, nearly landlocked bodies of water. The salinity of water bodies varies widely, being lower near the surface and the mouths of large rivers and higher in
18476-479: The sea and all the major groups of animals are represented there. Scientists differ as to precisely where in the sea life arose: the Miller-Urey experiments suggested a dilute chemical "soup" in open water, but more recent suggestions include volcanic hot springs, fine-grained clay sediments, or deep-sea " black smoker " vents, all of which would have provided protection from damaging ultraviolet radiation which
18625-436: The sea could be considered as brackish . Meanwhile, the Red Sea is very salty due to its high evaporation rate. Sea temperature depends on the amount of solar radiation falling on its surface. In the tropics, with the sun nearly overhead, the temperature of the surface layers can rise to over 30 °C (86 °F) while near the poles the temperature in equilibrium with the sea ice is about −2 °C (28 °F). There
18774-537: The sea level has been higher than it is today. The main factor affecting sea level over time is the result of changes in the oceanic crust, with a downward trend expected to continue in the very long term. At the last glacial maximum , some 20,000 years ago, the sea level was about 125 metres (410 ft) lower than in present times (2012). For at least the last 100 years, sea level has been rising at an average rate of about 1.8 millimetres (0.071 in) per year. Most of this rise can be attributed to an increase in
18923-399: The sea under the influence of gravity. A tsunami is an unusual form of wave caused by an infrequent powerful event such as an underwater earthquake or landslide, a meteorite impact, a volcanic eruption or a collapse of land into the sea. These events can temporarily lift or lower the surface of the sea in the affected area, usually by a few feet. The potential energy of the displaced seawater
19072-671: The sea, separated from the ocean by mountains or other natural geologic features that prevent the water draining away. The Caspian Sea is the largest one of these. Its main inflow is from the River Volga , there is no outflow and the evaporation of water makes it saline as dissolved minerals accumulate. The Aral Sea in Kazakhstan and Uzbekistan, and Pyramid Lake in the western United States are further examples of large, inland saline water-bodies without drainage. Some endorheic lakes are less salty, but all are sensitive to variations in
19221-657: The seabed provides a range of habitats on or under the surface of the substrate which are used by creatures adapted to these conditions. The tidal zone with its periodic exposure to the dehydrating air is home to barnacles , molluscs and crustaceans . The neritic zone has many organisms that need light to flourish. Here, among algal-encrusted rocks live sponges , echinoderms , polychaete worms, sea anemones and other invertebrates. Corals often contain photosynthetic symbionts and live in shallow waters where light penetrates. The extensive calcareous skeletons they extrude build up into coral reefs which are an important feature of
19370-427: The seabed. These provide a biodiverse habitat for reef-dwelling organisms. There is less sea life on the floor of deeper seas but marine life also flourishes around seamounts that rise from the depths, where fish and other animals congregate to spawn and feed. Close to the seabed live demersal fish that feed largely on pelagic organisms or benthic invertebrates. Exploration of the deep sea by submersibles revealed
19519-481: The seas, which offers a wide range of marine habitats and ecosystems , ranging vertically from the sunlit surface and shoreline to the great depths and pressures of the cold, dark abyssal zone , and in latitude from the cold waters under polar ice caps to the warm waters of coral reefs in tropical regions . Many of the major groups of organisms evolved in the sea and life may have started there. The ocean moderates Earth's climate and has important roles in
19668-418: The slope under the effect of gravity. The larger the breaking waves, the longer the beach and the more oblique the wave approach, the stronger is the longshore current. These currents can shift great volumes of sand or pebbles, create spits and make beaches disappear and water channels silt up. A rip current can occur when water piles up near the shore from advancing waves and is funnelled out to sea through
19817-535: The so-called "Northwest Africa" meteorites. When they get classified, they are named "Northwest Africa" (abbreviated NWA) followed by a number. It is generally accepted that NWA meteorites originate in Morocco, Algeria, Western Sahara, Mali, and possibly even further afield. Nearly all of these meteorites leave Africa through Morocco. Scores of important meteorites, including Lunar and Martian ones, have been discovered and made available to science via this route. A few of
19966-455: The structure of the metal may be affected by heat up to 1 centimetre (0.39 in) below the surface. Reports vary; some meteorites are reported to be "burning hot to the touch" upon landing, while others are alleged to have been cold enough to condense water and form a frost. Meteoroids that disintegrate in the atmosphere may fall as meteorite showers, which can range from only a few up to thousands of separate individuals. The area over which
20115-429: The sun, the weather conditions and the turbidity of the water. Much light gets reflected at the surface, and red light gets absorbed in the top few metres. Yellow and green light reach greater depths, and blue and violet light may penetrate as deep as 1,000 metres (3,300 ft). There is insufficient light for photosynthesis and plant growth beyond a depth of about 200 metres (660 ft). Over most of geologic time,
20264-430: The surface and loops back on itself. It takes a thousand years for this circulation pattern to be completed. Besides gyres, there are temporary surface currents that occur under specific conditions. When waves meet a shore at an angle, a longshore current is created as water is pushed along parallel to the coastline. The water swirls up onto the beach at right angles to the approaching waves but drains away straight down
20413-495: The surface at their terminal velocity and, at most, create a small pit. Large meteoroids may strike the earth with a significant fraction of their escape velocity (second cosmic velocity), leaving behind a hypervelocity impact crater. The kind of crater will depend on the size, composition, degree of fragmentation, and incoming angle of the impactor. The force of such collisions has the potential to cause widespread destruction. The most frequent hypervelocity cratering events on
20562-473: The surface layer and it remains there for much longer periods of time. Thermohaline circulation exchanges carbon between these two layers. Carbon enters the ocean as atmospheric carbon dioxide dissolves in the surface layers and is converted into carbonic acid , carbonate , and bicarbonate : It can also enter through rivers as dissolved organic carbon and is converted by photosynthetic organisms into organic carbon. This can either be exchanged throughout
20711-453: The temperature of the sea due to climate change , and the resulting slight thermal expansion of the upper 500 metres (1,600 ft) of water. Additional contributions, as much as one quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human needs. Wind blowing over the surface of a body of water forms waves that are perpendicular to
20860-645: The total number of well-described meteorites found in Algeria and Libya to more than 500. Meteorite markets came into existence in the late 1990s, especially in Morocco . This trade was driven by Western commercialization and an increasing number of collectors. The meteorites were supplied by nomads and local people who combed the deserts looking for specimens to sell. Many thousands of meteorites have been distributed in this way, most of which lack any information about how, when, or where they were discovered. These are
21009-432: The two can produce broken, irregular seas. Constructive interference can cause individual (unexpected) rogue waves much higher than normal. Most waves are less than 3 m (10 ft) high and it is not unusual for strong storms to double or triple that height; offshore construction such as wind farms and oil platforms use metocean statistics from measurements in computing the wave forces (due to for instance
21158-431: The upper layers, the major part of the ocean exists in permanent darkness. As the different depth and temperature zones each provide habitat for a unique set of species, the marine environment as a whole encompasses an immense diversity of life. Marine habitats range from surface water to the deepest oceanic trenches , including coral reefs, kelp forests , seagrass meadows , tidepools , muddy, sandy and rocky seabeds, and
21307-607: The use of the metal found in meteorites is also recorded in myths of many countries and cultures where the celestial source was often acknowledged, scientific documentation only began in the last few centuries. Meteorite falls may have been the source of cultish worship . The cult in the Temple of Artemis at Ephesus, one of the Seven Wonders of the Ancient World , possibly originated with the observation and recovery of
21456-460: The water sinks. From the deep sea near Greenland, such water flows southwards between the continental landmasses on either side of the Atlantic. When it reaches the Antarctic, it is joined by further masses of cold, sinking water and flows eastwards. It then splits into two streams that move northwards into the Indian and Pacific Oceans. Here it is gradually warmed, becomes less dense, rises towards
21605-426: The wave reaches a point where its deepest oscillations of the water contact the seabed , they begin to slow down. This pulls the crests closer together and increases the waves' height , which is called wave shoaling . When the ratio of the wave's height to the water depth increases above a certain limit, it " breaks ", toppling over in a mass of foaming water. This rushes in a sheet up the beach before retreating into
21754-445: The world ocean, so global climate modelling makes use of ocean circulation models as well as models of other major components such as the atmosphere , land surfaces, aerosols and sea ice. Ocean models make use of a branch of physics, geophysical fluid dynamics , that describes the large-scale flow of fluids such as seawater. Surface currents only affect the top few hundred metres of the sea, but there are also large-scale flows in
21903-588: The world's collections started with the discovery by Harvey H. Nininger that meteorites are much more common on the surface of the Earth than was previously thought. Nininger's strategy was to search for meteorites in the Great Plains of the United States, where the land was largely cultivated and the soil contained few rocks. Between the late 1920s and the 1950s, he traveled across the region, educating local people about what meteorites looked like and what to do if they thought they had found one, for example, in
22052-466: Was launched in 2007 and has collected a few meteorites. The combined efforts of all of these expeditions have produced more than 23,000 classified meteorite specimens since 1974, with thousands more that have not yet been classified. For more information see the article by Harvey (2003). At about the same time as meteorite concentrations were being discovered in the cold desert of Antarctica, collectors discovered that many meteorites could also be found in
22201-407: Was not blocked by the early Earth's atmosphere. Marine habitats can be divided horizontally into coastal and open ocean habitats. Coastal habitats extend from the shoreline to the edge of the continental shelf . Most marine life is found in coastal habitats, even though the shelf area occupies only 7 percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of
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