50-714: The Purbeck Hills , also called the Purbeck Ridge or simply the Purbecks , are a ridge of chalk downs in Dorset , England. The ridge is formed by the structure known as the Purbeck Monocline , and extends from Lulworth Cove in the west to Old Harry Rocks in the east, where it meets the sea. The hills are part of a system of chalk downlands in southern England formed from the Chalk Group which also includes Salisbury Plain and
100-408: A phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell (called a " test ") of diverse forms and materials. Tests of chitin (found in some simple genera, and Textularia in particular) are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within
150-466: A test , or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure. These shells are commonly made of calcium carbonate ( CaCO 3 ) or agglutinated sediment particles. Over 50,000 species are recognized, both living (6,700–10,000) and fossil (40,000). They are usually less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm. In modern scientific English,
200-506: A few are more recent. A mixture of chalk and mercury can be used as fingerprint powder . However, because of the toxicity of the mercury, the use of such mixtures for fingerprinting was abandoned in 1967. Foraminifera " Monothalamea " Tubothalamea Globothalamea incertae sedis Foraminifera ( / f ə ˌ r æ m ə ˈ n ɪ f ə r ə / fə- RAM -ə- NIH -fə-rə ; Latin for "hole bearers"; informally called " forams ") are single-celled organisms , members of
250-556: A host of larger organisms, including invertebrates, fish, shorebirds, and other foraminifera. It has been suggested, however, that in some cases predators may be more interested in the calcium from foram shells than in the organisms themselves. Several aquatic snail species are known to selectively feed upon foraminifera, often even preferring individual species. Certain benthic foraminifera have been found to be capable of surviving anoxic conditions for over 24 hours, indicating that they are capable of selective anaerobic respiration . This
300-653: A major group within the Protozoa known as the Rhizaria . Prior to the recognition of evolutionary relationships among the members of the Rhizaria, the Foraminifera were generally grouped with other amoeboids as phylum Rhizopodea (or Sarcodina) in the class Granuloreticulosa. The Rhizaria are problematic, as they are often called a "supergroup", rather than using an established taxonomic rank such as phylum . Cavalier-Smith defines
350-467: A nerve tube. Alcide d'Orbigny , in his 1826 work, considered them to be a group of minute cephalopods and noted their odd morphology, interpreting the pseudopodia as tentacles and noting the highly reduced (in actuality, absent) head. He named the group foraminifères , or "hole-bearers", as members of the group had holes in the divisions between compartments in their shells, in contrast to nautili or ammonites . The protozoan nature of foraminifera
400-400: A single opening or through many perforations in the test. Individual pseudopods characteristically have small granules streaming in both directions. Foraminifera are unique in having granuloreticulose pseudopodia ; that is, their pseudopodia appear granular under the microscope; these pseudopodia are often elongate and may split and rejoin each other. These can be extended and retracted to suit
450-633: Is mined from chalk deposits both above ground and underground . Chalk mining boomed during the Industrial Revolution , due to the need for chalk products such as quicklime and bricks . Most people first encounter chalk in school where it refers to blackboard chalk , which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or
500-610: Is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or skeletons of plankton , such as foraminifera or coccolithophores . These fragments mostly take the form of calcite plates ranging from 0.5 to 4 microns in size, though about 10% to 25% of a typical chalk is composed of fragments that are 10 to 100 microns in size. The larger fragments include intact plankton skeletons and skeletal fragments of larger organisms, such as molluscs , echinoderms , or bryozoans . Chalk
550-404: Is a soft, white, porous , sedimentary carbonate rock . It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor . Chalk is common throughout Western Europe , where deposits underlie parts of France, and steep cliffs are often seen where they meet the sea in places such as
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#1732854904443600-449: Is also common in the group, and at least some species can take advantage of dissolved organic carbon . A few foram species are parasitic , infecting sponges, molluscs, corals, or even other foraminifera. Parasitic strategies vary; some act as ectoparasites, using their pseudopodia to steal food from the host, while others burrow through the shell or body wall of their host to feed on its soft tissue. Foraminifera are themselves eaten by
650-508: Is also the only form of limestone that commonly shows signs of compaction. Flint (a type of chert ) is very common as bands parallel to the bedding or as nodules in seams , or linings to fractures , embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint). Chalk
700-428: Is applied to the hands and feet to remove perspiration and reduce slipping. Chalk may also be used as a house construction material instead of brick or wattle and daub : quarried chalk was cut into blocks and used as ashlar , or loose chalk was rammed into blocks and laid in mortar. There are still houses standing which have been constructed using chalk as the main building material. Most are pre- Victorian though
750-518: Is commonly used as a drying agent to obtain better grip by gymnasts and rock climbers. Glazing putty mainly contains chalk as a filler in linseed oil . Chalk and other forms of limestone may be used for their properties as a base . Chalk is a source of quicklime by thermal decomposition , or slaked lime following quenching of quicklime with water. In agriculture , chalk is used for raising pH in soils with high acidity . Small doses of chalk can also be used as an antacid . Additionally,
800-536: Is interpreted as an adaptation to survive changing oxygenic conditions near the sediment-water interface. Foraminifera are found in the deepest parts of the ocean such as the Mariana Trench , including the Challenger Deep , the deepest part known. At these depths, below the carbonate compensation depth , the calcium carbonate of the tests is soluble in water due to the extreme pressure. The Foraminifera found in
850-571: Is now usually made of talc (magnesium silicate). Chalk beds form important petroleum reservoirs in the North Sea and along the Gulf Coast of North America. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps
900-415: Is recognizable as being Elphidium . Early workers classified foraminifera within the genus Nautilus , noting their similarity to certain cephalopods . It was recognised by Lorenz Spengler in 1781 that foraminifera had holes in the septa, which would eventually grant the group its name. Spengler also noted that the septa of foraminifera arced the opposite way from those of nautili and that they lacked
950-586: Is so common in Cretaceous marine beds that the Cretaceous Period was named for these deposits. The name Cretaceous was derived from Latin creta , meaning chalk . Some deposits of chalk were formed after the Cretaceous. The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent , England, as well as their counterparts of
1000-401: Is typically almost pure calcite, CaCO 3 , with just 2% to 4% of other minerals. These are usually quartz and clay minerals , though collophane (cryptocrystalline apatite , a phosphate mineral) is also sometimes present, as nodules or as small pellets interpreted as fecal pellets. In some chalk beds, the calcite has been converted to dolomite , CaMg(CO 3 ) 2 , and in a few cases
1050-723: The Cap Blanc Nez on the other side of the Dover Strait . The Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage . Some of the highest chalk cliffs in the world occur at Jasmund National Park in Germany and at Møns Klint in Denmark . Chalk deposits are also found in Cretaceous beds on other continents, such as the Austin Chalk , Selma Group , and Niobrara Formations of
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#17328549044431100-525: The Dover cliffs on the Kent coast of the English Channel . Chalk is mined for use in industry, such as for quicklime , bricks and builder's putty , and in agriculture , for raising pH in soils with high acidity . It is also used for " blackboard chalk " for writing and drawing on various types of surfaces, although these can also be manufactured from other carbonate-based minerals, or gypsum . Chalk
1150-632: The English Civil War of the 17th century, when it was slighted . Some of the ridge, around the village of Tyneham , near Lulworth , has been closed to the public for use by the army as a firing range. This has protected them from damage from farming and development, and these areas are now nature reserves. At the eastern end Ballard Down is a National Trust nature reserve which is managed for its calcareous grassland habitat . 50°38′N 2°07′W / 50.633°N 2.117°W / 50.633; -2.117 Chalk Chalk
1200-615: The South Downs . For most of their length the chalk of the Purbeck Hills is protected from coastal erosion by a band of resistant Portland limestone . Where this band ends, at Durlston Head , the clay and chalk behind has been eroded, creating Poole Bay and the Solent . The ridge of steeply dipping chalk that forms the Purbeck Hills continues further east on the Isle of Wight . The height of
1250-530: The green algae , red algae , golden algae , diatoms , and dinoflagellates . These mixotrophic foraminifers are particularly common in nutrient-poor oceanic waters. Some forams are kleptoplastic , retaining chloroplasts from ingested algae to conduct photosynthesis . Most foraminifera are heterotrophic, consuming smaller organisms and organic matter; some smaller species are specialised feeders on phytodetritus , while others specialise in consuming diatoms. Some benthic forams construct feeding cysts, using
1300-512: The seafloor sediment (i.e., are benthic , with different sized species playing a role within the macrobenthos , meiobenthos , and microbenthos ), while a smaller number float in the water column at various depths (i.e., are planktonic ), which belong to the suborder Globigerinina . Fewer are known from freshwater or brackish conditions, and some very few (nonaquatic) soil species have been identified through molecular analysis of small subunit ribosomal DNA . Foraminifera typically produce
1350-514: The 5th century BCE noted them as making up the rock that forms the Great Pyramid of Giza . These are today recognized as representatives of the genus Nummulites . Strabo , in the 1st Century BCE, noted the same foraminifera, and suggested that they were the remains of lentils left by the workers who built the pyramids. Robert Hooke observed a foraminifera under the microscope, as described and illustrated in his 1665 book Micrographia : I
1400-474: The Foraminifera has varied since Schultze in 1854, who referred to as an order, Foraminiferida. Loeblich (1987) and Tappan (1992) reranked Foraminifera as a class as it is now commonly regarded. The Foraminifera have typically been included in the Protozoa , or in the similar Protoctista or Protist kingdom . Compelling evidence, based primarily on molecular phylogenetics , exists for their belonging to
1450-698: The North American interior. Chalk is also found in western Egypt (Khoman Formation) and western Australia ( Miria Formation ). Chalk of Oligocene to Neogene age has been found in drill cores of rock under the Pacific Ocean at Stewart Arch in the Solomon Islands . There are layers of chalk, containing Globorotalia , in the Nicosia Formation of Cyprus , which formed during the Pliocene . Chalk
1500-505: The Rhizaria as an infra-kingdom within the kingdom Protozoa. Some taxonomies put the Foraminifera in a phylum of their own, putting them on par with the amoeboid Sarcodina in which they had been placed. Although as yet unsupported by morphological correlates, molecular data strongly suggest the Foraminifera are closely related to the Cercozoa and Radiolaria , both of which also include amoeboids with complex shells; these three groups make up
1550-524: The Rhizaria. However, the exact relationships of the forams to the other groups and to one another are still not entirely clear. Foraminifera are closely related to testate amoebae . The most striking aspect of most foraminifera are their hard shells, or tests. These may consist of one of multiple chambers, and may be composed of protein, sediment particles, calcite, aragonite, or (in one case) silica. Some foraminifera lack tests entirely. Unlike other shell-secreting organisms, such as molluscs or corals ,
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1600-548: The chalk came mostly form low-magnesium calcite skeletons, so the sediments were already in the form of highly stable low-magnesium calcite when deposited. This is in contrast with most other limestones, which formed from high-magnesium calcite or aragonite that rapidly converted to the more stable low-magnesium calcite after deposition, resulting in the early cementation of such limestones. In chalk, absence of this calcium carbonate conversion process prevented early cementation, which partially accounts for chalk's high porosity. Chalk
1650-402: The chalk ridge and proximity to Poole Harbour and the south coast have made the hills of strategic importance. There are a number of Iron Age , Roman and Saxon archaeological sites, such as Nine Barrow Down . At Corfe Castle the hills are broken twice leaving a steep round hill between the ridges on which stood a medieval castle, guarding the only easy route through the hills, until
1700-485: The dolomitized chalk has been dedolomitized back to calcite. Chalk is highly porous, with typical values of porosity ranging from 35 to 47 per cent. While it is similar in appearance to both gypsum and diatomite , chalk is identifiable by its hardness, fossil content, and its reaction to acid (it produces effervescence on contact). In Western Europe, chalk was formed in the Late Cretaceous Epoch and
1750-793: The dominant scheme of classification until Tappan and Loeblich's 1964 classification, which placed foraminifera into the general groupings still used today, based on microstructure of the test wall. These groups have been variously moved around according to different schemes of higher-level classification. Pawlowski's (2013) use of molecular systematics has generally confirmed Tappan and Loeblich's groupings, with some being found as polyphyletic or paraphyletic; this work has also helped to identify higher-level relationships among major foraminiferal groups. "Monothalamids" (paraphyletic) Lagenida "Monothalamids" Miliolida Spirillinida "Monothalamids" Xenophyophorea " Textulariida " (paraphyletic) Robertinida Rotaliida The taxonomic position of
1800-437: The early Palaeocene Epoch (between 100 and 61 million years ago). It was deposited on extensive continental shelves at depths between 100 and 600 metres (330 and 1,970 ft), during a time of nonseasonal (likely arid) climate that reduced the amount of erosion from nearby exposed rock. The lack of nearby erosion explains the high purity of chalk. The coccolithophores, foraminifera, and other microscopic organisms from which
1850-490: The exact purpose of these is unclear, but they have been suggested to function as a reservoir of nitrate. Mitochondria are distributed evenly throughout the cell, though in some species they are concentrated under the pores and around the external margin of the cell. This has been hypothesised to be an adaptation to low-oxygen environments. Several species of xenophyophore have been found to have unusually high concentrations of radioactive isotopes within their cells, among
1900-666: The highest of any eukaryote. The purpose of this is unknown. Modern Foraminifera are primarily marine organisms, but living individuals have been found in brackish, freshwater and even terrestrial habitats. The majority of the species are benthic , and a further 50 morphospecies are planktonic . This count may, however, represent only a fraction of actual diversity, since many genetically distinct species may be morphologically indistinguishable. Benthic foraminifera are typically found in fine-grained sediments, where they actively move between layers; however, many species are found on hard rock substrates, attached to seaweeds, or sitting atop
1950-729: The idea that multiple different characters must separate taxonomic groups, and as such placed agglutinated and calcareous genera in close relation. This overall scheme of classification would remain until Cushman 's work in the late 1920s. Cushman viewed wall composition as the single most important trait in classification of foraminifera; his classification became widely accepted but also drew criticism from colleagues for being "not biologically sound". Geologist Irene Crespin undertook extensive research in this field, publishing some ninety papers—including notable work on foraminifera—as sole author as well as more than twenty in collaboration with other scientists. Cushman's scheme nevertheless remained
2000-528: The mineral gypsum ( calcium sulfate ). While gypsum-based blackboard chalk is the lowest cost to produce, and thus widely used in the developing world , use of carbonate-based chalk produces larger particles and thus less dust, and it is marketed as "dustless chalk". Coloured chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often coloured), used to draw on sidewalks , streets, and driveways , are primarily made of gypsum rather than calcium carbonate chalk. Magnesium carbonate chalk
2050-557: The most famous is the extensive complex at Grimes Graves in Norfolk . Chalk was traditionally used in recreation. In field sports, such as tennis played on grass, powdered chalk was used to mark the boundary lines of the playing field or court. If a ball hits the line, a cloud of chalk or pigment dust will be visible. In recent years, powdered chalk has been replaced with titanium dioxide . In gymnastics, rock-climbing, weightlifting and tug of war , chalk — now usually magnesium carbonate —
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2100-470: The needs of the cell. The pseudopods are used for locomotion, anchoring, excretion, test construction and in capturing food, which consists of small organisms such as diatoms or bacteria. Aside from the tests, foraminiferal cells are supported by a cytoskeleton of microtubules, which are loosely arranged without the structure seen in other amoeboids. Forams have evolved special cellular mechanisms to quickly assemble and disassemble microtubules, allowing for
2150-424: The pseuodopodia to encyst themselves inside of sediment and organic particles. Certain foraminifera prey upon small animals such as copepods or cumaceans ; some forams even predate upon other forams, drilling holes into the tests of their prey. One group, the xenophyophores, has been suggested to farm bacteria within their tests, although studies have failed to find support for this hypothesis. Suspension feeding
2200-665: The rapid formation and retraction of elongated pseudopodia. In the gamont (sexual form), foraminifera generally have only a single nucleus, while the agamont (asexual form) tends to have multiple nuclei. In at least some species the nuclei are dimorphic, with the somatic nuclei containing three times as much protein and RNA than the generative nuclei. However, nuclear anatomy seems to be highly diverse. The nuclei are not necessarily confined to one chamber in multi-chambered species. Nuclei can be spherical or have many lobes. Nuclei are typically 30-50 μm in diameter. Some species of foraminifera have large, empty vacuoles within their cells;
2250-562: The sediment surface. The majority of planktonic foraminifera are found in the globigerinina , a lineage within the rotaliida . However, at least one other extant rotaliid lineage, Neogallitellia , seems to have independently evolved a planktonic lifestyle. Further, it has been suggested that some Jurassic fossil foraminifera may have also independently evolved a planktonic lifestyle, and may be members of Robertinida. A number of forams, both benthic and planktonic, have unicellular algae as endosymbionts , from diverse lineages such as
2300-436: The small particles of chalk make it a substance ideal for cleaning and polishing. For example, toothpaste commonly contains small amounts of chalk, which serves as a mild abrasive . Polishing chalk is chalk prepared with a carefully controlled grain size, for very fine polishing of metals. French chalk (also known as tailor's chalk) is traditionally a hard chalk used to make temporary markings on cloth, mainly by tailors . It
2350-408: The term foraminifera is both singular and plural (irrespective of the word's Latin derivation), and is used to describe one or more specimens or taxa: its usage as singular or plural must be determined from context. Foraminifera is frequently used informally to describe the group, and in these cases is generally lowercase. The earliest known reference to foraminifera comes from Herodotus , who in
2400-417: The tests of foraminifera are located inside the cell membrane , within the protoplasm . The organelles of the cell are located within the compartment(s) of the test, and the hole(s) of the test allow the transfer of material from the pseudopodia to the internal cell and back. The foraminiferal cell is divided into granular endoplasm and transparent ectoplasm from which a pseudopodial net may emerge through
2450-513: Was first recognized by Dujardin in 1835. Shortly after, in 1852, d'Orbigny produced a classification scheme, recognising 72 genera of foraminifera, which he classified based on test shape—a scheme that drew severe criticism from colleagues. H.B. Brady 's 1884 monograph described the foraminiferal finds of the Challenger expedition . Brady recognized 10 families with 29 subfamilies, with little regard to stratigraphic range; his taxonomy emphasized
2500-529: Was trying several small and single Magnifying Glasses, and casually viewing a parcel of white Sand, when I perceiv'd one of the grains exactly shap'd and wreath'd like a Shell[...] I view'd it every way with a better Microscope and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell[...] Antonie van Leeuwenhoek described and illustrated foraminiferal tests in 1700, describing them as minute cockles; his illustration
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