Thorium is a weakly radioactive metallic chemical element with symbol Th and atomic number 90. Thorium is tarnishes black when it is exposed to air, forming thorium dioxide. Thorium is an electropositive actinide. All known thorium isotopes are unstable; the most stable isotope, 232Th, has a half-life of 14.05 billion years, or about the age of the universe. In the universe, thorium and uranium are the only three radioactive elements that still occur in large quantities as primordial elements, it is estimated to be over three times as abundant as uranium in the Earth's crust, is chiefly refined from monazite sands as a by-product of extracting rare-earth metals. Thorium was discovered in 1829 by the Norwegian amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jacob Berzelius, who named it after Thor, the Norse god of thunder, its first applications were developed in the late 19th century. Thorium's radioactivity was acknowledged during the first decades of the 20th century.
In the second half of the century, thorium was replaced in many uses due to concerns about its radioactivity. Thorium is still being used as an alloying element in TIG welding electrodes but is being replaced in the field with different compositions, it was material in high-end optics and scientific instrumentation, as the light source in gas mantles, but these uses have become marginal. It has been suggested as a replacement for uranium as nuclear fuel in nuclear reactors, several thorium reactors have been built. Thorium is a moderately soft, bright silvery radioactive actinide metal. In the periodic table, it lies to the right of actinium, to the left of protactinium, below cerium. Pure thorium is ductile and, as normal for metals, can be cold-rolled and drawn. At room temperature, thorium metal has a face-centred cubic crystal structure. Thorium metal has a bulk modulus of about the same as tin's. Aluminium's is 75.2 GPa. Thorium is about as hard as soft steel, so when heated it can be rolled into sheets and pulled into wire.
Thorium is harder than either of them. It becomes superconductive below 1.4 K. Thorium's melting point of 1750 °C is above both those of actinium and protactinium. At the start of period 7, from francium to thorium, the melting points of the elements increase, because the number of delocalised electrons each atom contributes increases from one in francium to four in thorium, leading to greater attraction between these electrons and the metal ions as their charge increases from one to four. After thorium, there is a new downward trend in melting points from thorium to plutonium, where the number of f electrons increases from about 0.4 to about 6: this trend is due to the increasing hybridisation of the 5f and 6d orbitals and the formation of directional bonds resulting in more complex crystal structures and weakened metallic bonding. Among the actinides up to californium, which can be studied in at least milligram quantities, thorium has the highest melting and boiling points and second-lowest density.
Thorium's boiling point of 4788 °C is the fifth-highest among all the elements with known boiling points. The properties of thorium vary depending on the degree of impurities in the sample; the major impurity is thorium dioxide. Experimental measurements of its density give values between 11.5 and 11.66 g/cm3: these are lower than the theoretically expected value of 11.7 g/cm3 calculated from thorium's lattice parameters due to microscopic voids forming in the metal when it is cast. These values lie between those of its neighbours actinium and protactinium, part of a trend across the early actinides. Thorium can form alloys with many other metals. Addition of small proportions of thorium improves the mechanical strength of magnesium, thorium-aluminum alloys have been considered as a way to store thorium in proposed future thorium nuclear reactors. Thorium forms eutectic mixtures with chromium and uranium, it is miscible in both solid and liquid states with its lighter congener cerium. All but two elements up to bismuth have an isotope, stable for all purposes, with the exceptions being technetium and promethium.
All elements from polonium onward are measurably radioactive. 232Th is one of the three nuclides beyond bismuth that have half-lives measured in billions of years. Four-fifths of the thorium present at Earth's formation has survived to the present. 232Th is the only isotope of thorium occurring in quantity in nature. Its stability is attributed to its closed nuclear shell with 142 neutrons. Thorium has a characteristic terrestrial isotopic composition, with atomic weight 232.0377. I
An ice core is a core sample, removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper, an ice core contains ice formed over a range of years. Cores are powered drills; the physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core. The proportions of different oxygen and hydrogen isotopes provide information about ancient temperatures, the air trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as carbon dioxide. Since heat flow in a large ice sheet is slow, the borehole temperature is another indicator of temperature in the past; these data can be combined to find the climate model. Impurities in ice cores may depend on location. Coastal areas are more to include material of marine origin, such as sea salt ions. Greenland ice cores contain layers of wind-blown dust that correlate with cold, dry periods in the past, when cold deserts were scoured by wind.
Radioactive elements, either of natural origin or created by nuclear testing, can be used to date the layers of ice. Some volcanic events that were sufficiently powerful to send material around the globe have left a signature in many different cores that can be used to synchronise their time scales. Ice cores have been studied since the early 20th century, several cores were drilled as a result of the International Geophysical Year. Depths of over 400 m were reached, a record, extended in the 1960s to 2164 m at Byrd Station in Antarctica. Soviet ice drilling projects in Antarctica include decades of work at Vostok Station, with the deepest core reaching 3769 m. Numerous other deep cores in the Antarctic have been completed over the years, including the West Antarctic Ice Sheet project, cores managed by the British Antarctic Survey and the International Trans-Antarctic Scientific Expedition. In Greenland, a sequence of collaborative projects began in the 1970s with the Greenland Ice Sheet Project.
An ice core is a vertical column through a glacier, sampling the layers that formed through an annual cycle of snowfall and melt. As snow accumulates, each layer presses on lower layers, making them denser until they turn into firn. Firn is not dense enough to prevent air from escaping; the depth at which this occurs varies with location, but in Greenland and the Antarctic it ranges from 64 m to 115 m. Because the rate of snowfall varies from site to site, the age of the firn when it turns to ice varies a great deal. At Summit Camp in Greenland, the depth is 77 m and the ice is 230 years old; as further layers build up, the pressure increases, at about 1500 m the crystal structure of the ice changes from hexagonal to cubic, allowing air molecules to move into the cubic crystals and form a clathrate. The bubbles disappear and the ice becomes more transparent. Two or three feet of snow may turn into less than a foot of ice; the weight above makes deeper layers of ice flow outwards. Ice is lost at the edges of the glacier to icebergs, or to summer melting, the overall shape of the glacier does not change much with time.
The outward flow can distort the layers, so it is desirable to drill deep ice cores at places where there is little flow. These can be located using maps of the flow lines. Impurities in the ice provide information on the environment from; these include soot and other types of particle from forest fires and volcanoes. The lowest layer of a glacier, called basal ice, is formed of subglacial meltwater that has refrozen, it can be up to about 20 m thick, though it has scientific value, it does not retain stratigraphic information. Cores are drilled in areas such as Antarctica and central Greenland where the temperature is never warm enough to cause melting, but the summer sun can still alter the snow. In polar areas, the sun night during the local summer and invisible all winter, it can make some snow sublimate, leaving so less dense. When the sun approaches its lowest point in the sky, the temperature drops and hoar frost forms on the top layer. Buried under the snow of following years, the coarse-grained hoar frost compresses into lighter layers than the winter snow.
As a result, alternating bands of lighter and darker ice can be seen in an ice core. Ice cores are collected by cutting around a cylinder of ice in a way that enables it to be brought to the surface. Early cores were collected with hand augers and they are still used for short holes. A design for ice core augers was patented in 1932 and they have changed little since. An auger is a cylinder with helical metal ribs wrapped around the outside, at the lower end of which are cutting blades. Hand augers can be rotated by a T handle or a brace handle, some can be attached to handheld electric drills to power the rotation. With the aid of a tripod for lowering and raising the auger, cores up to 50 m deep can be retri
The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from 541 to 251.902 million years ago, is subdivided into six geologic periods: the Cambrian, Silurian, Devonian and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era; the Paleozoic was a time of dramatic geological and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Arthropods, fish, amphibians and diapsids all evolved during the Paleozoic. Life began in the ocean but transitioned onto land, by the late Paleozoic, it was dominated by various forms of organisms. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, sophisticated diapsids and synapsids were dominant and the first modern plants appeared.
The Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover. Recovery of life in the sea may have been much faster; the Paleozoic era began and ended with supercontinents and in between were the rise of mountains along the continental margins, flooding and draining of shallow seas between the mountain ranges, in the interior of the continents. At its start, the supercontinent Pannotia broke up. Paleoclimatic studies and evidence of glaciers indicate that central Africa was most in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwana was forming. By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent of Pangaea and resulted in some of the great mountain chains, including the Appalachians, Ural Mountains, mountains of Tasmania.
There are six periods in the Paleozoic Era: Cambrian, Silurian, Devonian and the Permian. The Cambrian spans from 541 million years to 485 million years and is the first period of the Paleozoic era of the Phanerozoic; the Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any single period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, like trilobites. All marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, most of which became the supercontinent Gondwana; the Ordovician spanned from 485 million years to 443 million years ago. The Ordovician was a time in Earth's history in which many of the biological classes still prevalent today evolved, such as primitive fish and coral; the most common forms of life, were trilobites and shellfish. More the first arthropods went ashore to colonize the empty continent of Gondwana.
By the end of the Ordovician, Gondwana was at the south pole, early North America had collided with Europe, closing the Atlantic Ocean. Glaciation of Africa resulted in a major drop in sea level, killing off all life that had established along coastal Gondwana. Glaciation may have caused the Ordovician–Silurian extinction events, in which 60% of marine invertebrates and 25% of families became extinct, is considered the first mass extinction event and the second deadliest; the Silurian spanned from 443 to 416 million years ago. The Silurian saw the rejuvenation of life; this period saw the mass evolution of fish, as jawless fish became more numerous, jawed fish evolved, the first freshwater fish evolved, though arthropods, such as sea scorpions, were still apex predators. Terrestrial life evolved, including early arachnids and centipedes; the evolution of vascular plants allowed plants to gain a foothold on land. These early plants were the forerunners of all plant life on land. During this time, there were four continents: Gondwana, Laurentia and Avalonia.
The recent rise in sea levels allowed many new species to thrive in water. The Devonian spanned from 416 million years to 359 million years ago. Known as "The Age of the Fish", the Devonian featured a huge diversification of fish, including armored fish like Dunkleosteus and lobe-finned fish which evolved into the first tetrapods. On land, plant groups diversified in an event known as the Devonian Explosion when plants made lignin allowing taller growth and vascular tissue: the first trees evolved, as well as seeds; this event diversified arthropod life, by providing them new habitats. The first amphibians evolved, the fish were now at the top of the food chain. Near the end of the Devonian, 70% of all species became extinct in an event known as the Late Devonian extinction, the Earth's second mass extinction event; the Carboniferous spanned from 359 million to 299 million years ago. During this time, average global temperatures were exc
Isotope-ratio mass spectrometry
Isotope-ratio mass spectrometry is a specialization of mass spectrometry, in which mass spectrometric methods are used to measure the relative abundance of isotopes in a given sample. This technique has two different applications in environmental sciences; the analysis of'stable isotopes' is concerned with measuring isotopic variations arising from mass-dependent isotopic fractionation in natural systems. On the other hand, radiogenic isotope analysis involves measuring the abundances of decay-products of natural radioactivity, is used in most long-lived radiometric dating methods; the isotope-ratio mass spectrometer allows the precise measurement of mixtures of occurring isotopes. Most instruments used for precise determination of isotope ratios are of the magnetic sector type; this type of analyzer is superior to the quadrupole type in this field of research for two reasons. First, it can be set up for multiple-collector analysis, second, it gives high-quality'peak shapes'. Both of these considerations are important for isotope-ratio analysis at high precision and accuracy.
The sector-type instrument designed by Alfred Nier was such an advance in mass spectrometer design that this type of instrument is called the'Nier type'. In the most general terms the instrument operates by ionizing the sample of interest, accelerating it over a potential in the kilo-volt range, separating the resulting stream of ions according to their mass-to-charge ratio. Beams with lighter ions bend at a smaller radius; the current of each ion beam is measured using a'Faraday cup' or multiplier detector. Many radiogenic isotope measurements are made by ionization of a solid source, whereas stable isotope measurements of light elements are made in an instrument with a gas source. In a "multicollector" instrument, the ion collector has an array of Faraday cups, which allows the simultaneous detection of multiple isotopes. Measurement of natural variations in the abundances of stable isotopes of the same element is referred to as stable isotope analysis; this field is of interest because the differences in mass between different isotopes leads to isotope fractionation, causing measurable effects on the isotopic composition of samples, characteristic of their biological or physical history.
As a specific example, the hydrogen isotope deuterium is double the mass of the common hydrogen isotope. Water molecules containing the common hydrogen isotope have a mass of 18. Water incorporating a deuterium atom has a mass of 19, over 5% heavier; the energy to vaporise the heavy water molecule is higher than that to vaporize the normal water so isotope fractionation occurs during the process of evaporation. Thus a sample of sea water will exhibit a quite detectable isotopic-ratio difference when compared to Antarctic snowfall. Samples must be introduced to the mass spectrometer as pure gases, achieved through combustion, gas chromatographic feeds, or chemical trapping. By comparing the detected isotopic ratios to a measured standard, an accurate determination of the isotopic make up of the sample is obtained. For example, carbon isotope ratios are measured relative to the international standard for C; the C standard is produced from a fossil belemnite found in the Peedee Formation, a limestone formed in the Cretaceous period in South Carolina, U.
S. A; the fossil is referred to as VPDB and has 13C:12C ratio of 0.0112372. Oxygen isotope ratios are measured relative the standard, V-SMOW, it is critical that the sample be processed before entering the mass spectrometer so that only a single chemical species enters at a given time. Samples are combusted or pyrolyzed and the desired gas species is purified by means of traps, catalysts and/or chromatography; the two most common types of IRMS instruments are dual inlet. In dual inlet IRMS, purified gas obtained from a sample is alternated with a standard gas by means of a system of valves, so that a number of comparison measurements are made of both gases. In continuous flow IRMS, sample preparation occurs before introduction to the IRMS, the purified gas produced from the sample is measured just once; the standard gas may be measured before and after the sample or after a series of sample measurements. While continuous-flow IRMS instruments can achieve higher sample throughput and are more convenient to use than dual inlet instruments, the yielded data is of 10-fold lower precision.
A static gas mass spectrometer is one in which a gaseous sample for analysis is fed into the source of the instrument and left in the source without further supply or pumping throughout the analysis. This method can be used for'stable isotope' analysis of light gases, but it is used in the isotopic analysis of noble gases for radiometric dating or isotope geochemistry. Important examples are argon -- argon helium isotope analysis. Several of the isotope systems involved in radiometric dating depend on IRMS using thermal ionization of a solid sample loaded into the source of the mass spectrometer; these methods include rubidium–strontium dating, uranium–lead dating, lead–lead dating and samarium–neodymium dating. When these isotope ratios are measured by TIMS, mass-dependent fractionation occurs as species are emitted by the hot filament. Fractionation occurs due to the excitation of the sample and therefore must
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
Lead is a chemical element with symbol Pb and atomic number 82. It is a heavy metal, denser than most common materials. Lead is soft and malleable, has a low melting point; when freshly cut, lead is silvery with a hint of blue. Lead has the highest atomic number of any stable element and three of its isotopes each include a major decay chain of heavier elements. Lead is a unreactive post-transition metal, its weak metallic character is illustrated by its amphoteric nature. Compounds of lead are found in the +2 oxidation state rather than the +4 state common with lighter members of the carbon group. Exceptions are limited to organolead compounds. Like the lighter members of the group, lead tends to bond with itself. Lead is extracted from its ores. Galena, a principal ore of lead bears silver, interest in which helped initiate widespread extraction and use of lead in ancient Rome. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. In 2014, the annual global production of lead was about ten million tonnes, over half of, from recycling.
Lead's high density, low melting point and relative inertness to oxidation make it useful. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, batteries and shot, solders, fusible alloys, white paints, leaded gasoline, radiation shielding. In the late 19th century, lead's toxicity was recognized, its use has since been phased out of many applications. However, many countries still allow the sale of products that expose humans to lead, including some types of paints and bullets. Lead is a toxin that accumulates in soft tissues and bones, it acts as a neurotoxin damaging the nervous system and interfering with the function of biological enzymes, causing neurological disorders, such as brain damage and behavioral problems. A lead atom has 82 electrons, arranged in an electron configuration of 4f145d106s26p2; the sum of lead's first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, lead's upper neighbor in the carbon group.
This is unusual. The similarity of ionization energies is caused by the lanthanide contraction—the decrease in element radii from lanthanum to lutetium, the small radii of the elements from hafnium onwards; this is due to poor shielding of the nucleus by the lanthanide 4f electrons. The sum of the first four ionization energies of lead exceeds that of tin, contrary to what periodic trends would predict. Relativistic effects, which become significant in heavier atoms, contribute to this behavior. One such effect is the inert pair effect: the 6s electrons of lead become reluctant to participate in bonding, making the distance between nearest atoms in crystalline lead unusually long. Lead's lighter carbon group congeners form stable or metastable allotropes with the tetrahedrally coordinated and covalently bonded diamond cubic structure; the energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp3 orbitals. In lead, the inert pair effect increases the separation between its s- and p-orbitals, the gap cannot be overcome by the energy that would be released by extra bonds following hybridization.
Rather than having a diamond cubic structure, lead forms metallic bonds in which only the p-electrons are delocalized and shared between the Pb2+ ions. Lead has a face-centered cubic structure like the sized divalent metals calcium and strontium. Pure lead has a silvery appearance with a hint of blue, it tarnishes on contact with moist air and takes on a dull appearance, the hue of which depends on the prevailing conditions. Characteristic properties of lead include high density, malleability and high resistance to corrosion due to passivation. Lead's close-packed face-centered cubic structure and high atomic weight result in a density of 11.34 g/cm3, greater than that of common metals such as iron and zinc. This density is the origin of the idiom to go over like a lead balloon; some rarer metals are denser: tungsten and gold are both at 19.3 g/cm3, osmium—the densest metal known—has a density of 22.59 g/cm3 twice that of lead. Lead is a soft metal with a Mohs hardness of 1.5. It is somewhat ductile.
The bulk modulus of lead—a measure of its ease of compressibility—is 45.8 GPa. In comparison, that of aluminium is 75.2 GPa. Lead's tensile strength, at 12–17 MPa, is low; the melting point of lead—at 327.5 °C —is low compared to most metals. Its boiling point of 1749 °C is the lowest among the carbon group elements; the electrical resistivity of lead at 20 °C is 192 nanoohm-meters an order of magnitude higher than those of other industrial metals. Lead is a superconductor at temperatures lower than 7.19 K.
Foraminifera are members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses. Tests of chitin are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment, while a smaller variety float in the water column at various depths. Fewer are known from freshwater or brackish conditions, some few soil species have been identified through molecular analysis of small subunit ribosomal DNA. Foraminifera produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure; these shells are made of calcium carbonate or agglutinated sediment particles. Over 50,000 species are recognized, both fossil, they are less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm. In modern Scientific English, the term foraminifera is both singular and plural, is used to describe one or more specimens or taxa: its usage as singular or plural must be determined from context.
Foraminifera is used informally to describe the group, in these cases is lowercase. The taxonomic position of the Foraminifera has varied since their recognition as protozoa by Schultze in 1854, there referred to as an order, Foraminiferida. Loeblich and Tappan reranked Foraminifera as a class as it is now regarded; the Foraminifera have been included in the Protozoa, or in the similar Protoctista or Protist kingdom. Compelling evidence, based on molecular phylogenetics, exists for their belonging to 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 grouped with other amoeboids as phylum Rhizopodea in the class Granuloreticulosa; the Rhizaria are problematic, as they are called a "supergroup", rather than using an established taxonomic rank such as phylum. Cavalier-Smith defines 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 suggest the Foraminifera are related to the Cercozoa and Radiolaria, both of which include amoeboids with complex shells. However, the exact relationships of the forams to the other groups and to one another are still not clear. Foraminifera are related to testate amoebae; the most recent taxonomy by Mikhalevich 2013. Foraminifera d'Orbigny 1826 Order Reticulomyxida Class Schizocladea Cedhagen & Mattson 1992 Order Schizocladida Class Xenophyophorea Schultze 1904 Order Stannomida Tendal 1972 Order Psamminida Tendal 1972 Class Astrorhizata Saidova 1981 Subclass Lagynana Mikhalevich 1980 Order Ammoscalariida Mikhalevich 1980 Order Lagynida Mikhalevich 1980 Order Allogromiida Loeblich & Tappan 1961 Subclass Astrorhizana Saidova 1981 Order Astrorhizida Lankester 1885 Order Dendrophryida Mikhalevich 1995 Order Hippocrepinida Saidova 1981 Order †Parathuramminida Mikhalevich 1980 Order Psammosphaerida Haeckel 1894 Class Rotaliata Mikhalevich 1980 Subclass Globigerinana Mikhalevich 1980 Order Cassigerinellida Mikhalevich 2013 Order Globigerinida Carpenter, Parker & Jones 1862 Order Hantkeninida Mikhalevich 1980 Order Heterohelicida Fursenko 1958 Order Globorotaliida Mikhalevich 1980 Subclass Textulariana Mikhalevich 1980 Order Nautiloculinida Mikhalevich 2003 Order Spiroplectamminida Mikhalevich 1992 Order Textulariida Delage & Hérouard 1896 Order Trochamminida Saidova 1981 (Carterinida Loeblich & Tappan 1955] Order Verneuilinida Mikhalevich & Kaminski 2003 Subclass Rotaliana Mikhalevich 1980 Superorder Robertinoida Mikhalevich 1980 Order Robertinida Mikhalevich 1980 Superorder Nonionoida Saidova 1981 Order Elphidiida Saidova 1981 Order Nummulitida Carpenter, Parker & Jones 1862 Order †Orbitoidida Copeland 1956 Order Nonionida Saidova 1981 Superorder Buliminoida Saidova 1981 Order Cassidulinida d’Orbigny 1839 Order Buliminida Saidova 1981 Order Bolivinitida Saidova 1981 Superorder Discorboida Ehrenberg 1838 Order Chilostomellida Haeckel 1894 Order Discorbida Ehrenberg 1838 Order Glabratellida Mikhalevich 1994 Order Planorbulinida Mikhalevich 1992 Order Rotaliida Lankester 1885 Order Rosalinida Delage & Hérouard 1896 Class Nodosariata Mikhalevich 1992 Subclass Hormosinana Mikhalevich 1992 Order Ammomarginulinida Mikhalevich 2002 Order Nouriida Mikhalevich 1980 Order †Pseudopalmulida Mikhalevich 1992 Order Saccamminida Lankester 1885 Order Hormosinida Mikhalevich 1980 Subclass Nodosariana Mikhalevich 1992 Order †Biseriamminida Mikhalevich 1981 Order Delosinida Revets 1989 Order Lagenida Delage & Hérouard 1896 Order †Palaeotextulariida Hohenegger & Piller 1975 Order Polymorphinida Mikhalevich 1980 Order Vaginulinida Mikhalevich 1993 Order Nodosariida Calkins 1926 Class Spirillinata Mikhalevich 1992 Subclass Ammodiscana Mikhalevich 1980 Order †Plagioraphida Mikhalevich 2003 Order Ammodiscida Mikhalevich 1980 Order Ammovertellinida Mikhalevich 1999 Order Ataxophragmiida Fursenko 1958 Subclass Spirillinana Mikhalevich 1992 Superorder †Archaediscoida Pojarkov & Skvortsov 1979 Order †Archaediscida Pojarkov & Skvortsov 1979 Order †Lasiodiscida