1.
Antiarchi
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Antiarchi is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species, the pair of pectoral fins were modified into a pair of caliper-like, or arthropod-like limbs. In primitive forms, such as Yunnanolepis, the limbs were thick and short, while in advanced forms, such as Bothriolepis, below is a cladogram from Jia et al. Review of Antiarcha at Paleos Long, John A, the Rise of Fishes,500 Million Years of Evolution Baltimore, The Johns Hopkins University Press,1996. A compendium of fossil marine animal genera
2.
Ediacaran
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The Ediacaran Period, spans 94 million years from the end of the Cryogenian Period 635 million years ago, to the beginning of the Cambrian Period 541 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon and it is named after the Ediacara Hills of South Australia. The Ediacaran Period overlaps, but is shorter than the Vendian Period, the Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian. Paleontological substantiation of this boundary was worked out separately for the siliciclastic basin, the lower boundary of the Vendian was suggested to be defined at the base of the Varanger tillites. The Ediacaran Period represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils. Although the Ediacaran Period does contain soft-bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer that is referred to as a cap carbonate and this bed is characterized by an unusual depletion of 13C that indicates a sudden climatic change at the end of the Marinoan ice age. The lower boundary GSSP of the Ediacaran is at the base of the cap carbonate, immediately above the Elatina diamictite in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia. In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition, nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and ichnofossils are disputable. Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs. pedum in Namibia, Spain and Newfoundland, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The dating of the type section of the Ediacaran Period in South Australia has proven uncertain. Therefore, the age range assigned those rocks from 635 to 542 million years, is based on more precice dating in other locations is possible, the base age of approximately 635 million years is based on U-Pb isochron dating from Namibia and China. The fossil record from the Ediacaran Period is sparse, as more easily fossilized hard-shelled animals had yet to evolve, the Ediacaran biota include the oldest definite multicellular organisms, the most common types of which resemble segmented worms, fronds, disks, or immobile bags. Ediacara biota bear little resemblance to modern lifeforms, and their relationship even with the immediately following lifeforms of the Cambrian explosion is rather difficult to interpret. More than 100 genera have been described, and well known forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Onega, Pteridinium, there is evidence that Earths first mass extinction happened during this period when early animals changed the environment. The relative proximity of the Moon at this time meant that tides were stronger, the day was 21. 9±0.4 hours, and there were 13. 1±0.1 synodic months/year and 400±7 solar days/year. A few English language documentaries have featured the Ediacaran era and biota, the Geological History of Canada, as part of The Nature of Things series, CBC-SRC,2011, Eastern Canada. The first episode of a BBC documentary titled Life on Earth, with David Attenborough as narrator, another documentary narrated by David Attenborough titled First Life featuring Charnia, Dickinsonia, Spriggina, Funisia, and Kimberella animated in CGI
3.
Embryo
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An embryo is an early stage of development of a multicellular diploid eukaryotic organism. In general, in organisms that reproduce sexually, an embryo develops from a zygote, the zygote possesses half the DNA of each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism, the result of this process is an embryo. First attested in English in the mid-14c, the word embryon derives from Medieval Latin embryo, itself from Greek ἔμβρυον, lit. Young one, which is the neuter of ἔμβρυος, lit, growing in, from ἐν, in and βρύω, swell, be full, the proper Latinized form of the Greek term would be embryum. In animals, the development of the zygote into an embryo proceeds through specific stages of blastula, gastrula. The blastula stage typically features a fluid-filled cavity, the blastocoel, surrounded by a sphere or sheet of cells, in a placental mammal, an ovum is fertilized in a fallopian tube through which it travels into the uterus. An embryo is called a fetus at an advanced stage of development. In humans, this is from the week of gestation. During gastrulation the cells of the blastula undergo coordinated processes of cell division, invasion, in triploblastic organisms, the three germ layers are called endoderm, ectoderm, and mesoderm. The position and arrangement of the layers are highly species-specific, however. For example, in neurogenesis, a subpopulation of cells is set aside to become the brain, spinal cord. Modern developmental biology is extensively probing the molecular basis for every type of organogenesis, including angiogenesis, chondrogenesis, myogenesis, osteogenesis, and many others. In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem. Once the embryo begins to germinate — grow out from the seed — it is called a seedling, bryophytes and ferns also produce an embryo, but do not produce seeds. In these plants, the embryo begins its existence attached to the inside of the archegonium on a parental gametophyte from which the egg cell was generated, the structure and development of the rest of the embryo varies by group of plants. Once the embryo has expanded beyond the enclosing archegonium, it is no longer termed an embryo, embryos are used in various fields of research and in techniques of assisted reproductive technology. An egg may be fertilized in vitro and the embryo may be frozen for later use
4.
Doushantuo Formation
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The whole sequence sits on an unconformity with the underlying Liantuo Formation, which is free of fossils, an unconformity usually being interpreted as a period of erosion. This latest Cryogenian glacial level is dated ca 654 —635 Ma. The Doushantuo formation itself has three layers representing aquatic sediments that formed as sea levels rose with the melting of worldwide glaciation. Biomarkers indicate highly saline conditions, such as might be found in a lagoon, low oxygen levels, the richest finds lie at the bottom of the middle stratum, with a date about 570 Ma, thus from some time after the great Gaskiers glaciation of. Doushantuo fossils are all aquatic, microscopic, and preserved to a degree of detail. A nearly microscopic fossil animal, Vernanimalcula was announced in October 2005, an alternative interpretation suggests that it was created by non-biological rock-forming processes. The discovery was made when the phosphate deposits were being mined. The documented biota now includes phosphatized microfossils of algae, multicellular thallophytes, acritarchs, ciliates, there also seem to be what scientists cautiously report as bilateral animal embryos, termed Parapandorina, and eggs. An alternative possibility is that the embryos and eggs are in fact fossils of giant sulfur bacteria resembling Thiomargarita, the interpretation would also provide a mechanism for phosphatic fossilization through microbially mediated phosphate precipitation by the bacteria, which has been observed in modern environments. If dark spots in the fossil transpire to be fossilised nuclei - an unlikely claim - this would refute the Thiomargarita hypothesis. That being said, recent comparisons of the Doushantuo fossils to modern decaying Thiomargarita, the formation was laid down on a carbonate shelf, whose rim enclosed a lagoon between tidal flats on the shore, and the deeper ocean. The most recent Doushantuo rocks show a decrease in the 13C/12C carbon isotope ratio. Phosphatic fossilization Hagadorn, J. W. Xiao, S, Donoghue, PC, Bengtson, S, Gostling, NJ, Pawlowska, M, Raff, EC, Raff, RA, cellular and Subcellular Structure of Neoproterozoic Animal Embryos. Knoll, A. H. Three-dimensional preservation of algae and animal embryos in a Neoproterozoic phosphorite
5.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
6.
Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
7.
Incertae sedis
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Incertae sedis is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are referred to as enigmatic taxa. In the system of nomenclature, uncertainty at specific taxonomic levels is indicated by incertae familiae, incerti subordinis, incerti ordinis. The fossil plant Paradinandra suecica could not be assigned to any family, the fossil Gluteus minimus, described in 1975, could not be assigned to any known animal phylum. The genus is therefore incertae sedis within the kingdom Animalia, while it was unclear to which order the New World vultures should be assigned, they were placed in Aves incertae sedis. It was later agreed to them in a separate order. Bocages longbill, Amaurocichla bocagei, a species of passerine bird, since it is unclear to which family it belongs, it is classified as Passeroidea incertae sedis. HeLa cells, descended from human cervical cancer cells, may diverge genetically from normal human cells sufficiently to be categorized as a new species with largely incertae sedis taxonomy, when formally naming a taxon, uncertainty about its taxonomic classification can be problematic. Their reduced status was attributed largely to poor or inadequate descriptions and it is also evident that a proportion of the characters used in the analysis, or their given states for particular taxa, were inappropriate or invalid. Additional complexity, and factors that have misled earlier authorities, are intrusion by extensive homoplasies, apparent character state reversals and convergent evolution. If a formal analysis is conducted that does not include a certain taxon. This is particularly common when molecular phylogenies are generated, since tissue for many rare organisms is hard to obtain and it is also a common scenario when fossil taxa are included, since many fossils are defined based on partial information. If conflicting results exist or if there is not a consensus among researchers as to how a taxon relates to other organisms, for example, if a new species was given the specific epithet album by Anton and attributed with uncertainty to Agenus, it could be denoted Agenus. Album Anton, the indicates the author that assigned the question mark, so if Anton described Agenus album, and Bruno called the assignment into doubt, this could be denoted Agenus. Album, with the parentheses around Anton because the original assignment was modified by Bruno
8.
Synonym (taxonomy)
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For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies. This name is no longer in use, it is now a synonym of the current scientific name which is Picea abies, unlike synonyms in other contexts, in taxonomy a synonym is not interchangeable with the name of which it is a synonym. In taxonomy, synonyms are not equals, but have a different status, for any taxon with a particular circumscription, position, and rank, only one scientific name is considered to be the correct one at any given time. A synonym cannot exist in isolation, it is always an alternative to a different scientific name, given that the correct name of a taxon depends on the taxonomic viewpoint used a name that is one taxonomists synonym may be another taxonomists correct name. Synonyms may arise whenever the same taxon is described and named more than once, independently. They may also arise when existing taxa are changed, as when two taxa are joined to one, a species is moved to a different genus. To the general user of scientific names, in such as agriculture, horticulture, ecology, general science. A synonym is a name that was used as the correct scientific name but which has been displaced by another scientific name. Thus Oxford Dictionaries Online defines the term as a name which has the same application as another. In handbooks and general texts, it is useful to have mentioned as such after the current scientific name. Synonyms used in this way may not always meet the strict definitions of the synonym in the formal rules of nomenclature which govern scientific names. Changes of scientific name have two causes, they may be taxonomic or nomenclatural, a name change may be caused by changes in the circumscription, position or rank of a taxon, representing a change in taxonomic, scientific insight. A name change may be due to purely nomenclatural reasons, that is, based on the rules of nomenclature, the earliest such name is called the senior synonym, while the later name is the junior synonym. One basic principle of zoological nomenclature is that the earliest correctly published name, synonyms are important because if the earliest name cannot be used, then the next available junior synonym must be used for the taxon. Objective synonyms refer to taxa with the type and same rank. For example, John Edward Gray published the name Antilocapra anteflexa in 1855 for a species of pronghorn, however, it is now commonly accepted that his specimen was an unusual individual of the species Antilocapra americana published by George Ord in 1815. Ords name thus takes precedence, with Antilocapra anteflexa being a subjective synonym. Objective synonyms are common at the level of genera, because for various reasons two genera may contain the type species, these are objective synonyms
9.
Pro parte
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For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies. This name is no longer in use, it is now a synonym of the current scientific name which is Picea abies, unlike synonyms in other contexts, in taxonomy a synonym is not interchangeable with the name of which it is a synonym. In taxonomy, synonyms are not equals, but have a different status, for any taxon with a particular circumscription, position, and rank, only one scientific name is considered to be the correct one at any given time. A synonym cannot exist in isolation, it is always an alternative to a different scientific name, given that the correct name of a taxon depends on the taxonomic viewpoint used a name that is one taxonomists synonym may be another taxonomists correct name. Synonyms may arise whenever the same taxon is described and named more than once, independently. They may also arise when existing taxa are changed, as when two taxa are joined to one, a species is moved to a different genus. To the general user of scientific names, in such as agriculture, horticulture, ecology, general science. A synonym is a name that was used as the correct scientific name but which has been displaced by another scientific name. Thus Oxford Dictionaries Online defines the term as a name which has the same application as another. In handbooks and general texts, it is useful to have mentioned as such after the current scientific name. Synonyms used in this way may not always meet the strict definitions of the synonym in the formal rules of nomenclature which govern scientific names. Changes of scientific name have two causes, they may be taxonomic or nomenclatural, a name change may be caused by changes in the circumscription, position or rank of a taxon, representing a change in taxonomic, scientific insight. A name change may be due to purely nomenclatural reasons, that is, based on the rules of nomenclature, the earliest such name is called the senior synonym, while the later name is the junior synonym. One basic principle of zoological nomenclature is that the earliest correctly published name, synonyms are important because if the earliest name cannot be used, then the next available junior synonym must be used for the taxon. Objective synonyms refer to taxa with the type and same rank. For example, John Edward Gray published the name Antilocapra anteflexa in 1855 for a species of pronghorn, however, it is now commonly accepted that his specimen was an unusual individual of the species Antilocapra americana published by George Ord in 1815. Ords name thus takes precedence, with Antilocapra anteflexa being a subjective synonym. Objective synonyms are common at the level of genera, because for various reasons two genera may contain the type species, these are objective synonyms
10.
Micropaleontology
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Micropaleontology is the branch of palaeontology that studies microfossils, or fossils that require the use of a microscope to see the organism, its morphology and its characteristics details. Microfossils are fossils that are generally between 0. 001mm and 1 mm in size, the study of which requires the use of light or electron microscopy. Fossils which can be studied with the eye or low-powered magnification. For example, some organisms, such as Bryozoa have relatively large colonies. In another example, many genera of Foraminifera, which are protists are known from shells that were as big as coins. Microfossils are a feature of the geological record, from the Precambrian to the Holocene. They are most common in deposits of marine environments, but also occur in water, fresh water. This division reflects differences in the mineralogical and chemical composition of microfossil remains rather than any strict taxonomic or ecological distinctions, most researchers in this field, known as micropaleontologists, are typically specialists in one or more taxonomic groups. Calcareous microfossils include coccoliths, foraminifera, calcareous dinoflagellate cysts, phosphatic microfossils include conodonts, some scolecodonts, Shark spines and teeth, and other Fish remains. Siliceous microfossils include diatoms, radiolarians, silicoflagellates, ebridians, phytoliths, some scolecodonts, the study of organic microfossils is called palynology. Organic microfossils include pollen, spores, chitinozoans, scolecodonts, acritarchs, dinoflagellate cysts, the resulting concentrated sample of microfossils is then mounted on a slide for analysis, usually by light microscope. Taxa are then identified and counted, the enormous numbers of microfossils that a small sediment sample can often yield allows the collection of statistically robust datasets which can be subjected to multivariate analysis. A typical microfossil study will involve identification of a few hundred specimens from each sample, Microfossils are especially noteworthy for their importance in biostratigraphy. Since microfossils are often abundant, widespread, and quick to appear and disappear from the stratigraphic record. Microfossils, particularly from deep-sea sediments, also some of the most important records of global environmental change on long. Across vast areas of the floor, the shells of planktonic micro-organisms sinking from surface waters provide the dominant source of sediment. Study of changes in assemblages of microfossils and changes in their shell chemistry are fundamental to research on change in the geological past. Micropaleontology is also a tool of geoarchaeology used in the reconstruction of human habitation sites
11.
Cambrian explosion
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Lasting for about the next 20–25 million years, it resulted in the divergence of most modern metazoan phyla. Additionally, the event was accompanied by major diversification of other organisms, prior to the Cambrian explosion, most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 to 80 million years, the rate of diversification accelerated by an order of magnitude, almost all present animal phyla appeared during this period. There is strong evidence for species of Cnidaria and Porifera existing in the Ediacaran, bryozoans dont appear in the fossil record until after the Cambrium, in the Lower Ordovician. The Cambrian explosion has generated extensive scientific debate, interpretation is difficult due to a limited supply of evidence, based mainly on an incomplete fossil record and chemical signatures remaining in Cambrian rocks. The first discovered Cambrian fossils were trilobites, described by Edward Lhuyd, nineteenth-century geologists such as Adam Sedgwick and Roderick Murchison used the fossils for dating rock strata, specifically for establishing the Cambrian and Silurian periods. He reasoned that earlier seas had swarmed with living creatures, earlier fossil evidence has since been found. Fossils of more complex cells, from which all animals, plants. Rocks dating from 580 to 543 million years ago contain fossils of the Ediacara biota, organisms so large that they are likely multicelled, the most common organism, Marrella, was clearly an arthropod, but not a member of any known arthropod class. Stephen Jay Goulds popular 1989 account of work, Wonderful Life, brought the matter into the public eye. While differing significantly in details, both Whittington and Gould proposed that all animal phyla had appeared almost simultaneously in a rather short span of geological period. Other analyses, some recent and some dating back to the 1970s. Radiometric dates for much of the Cambrian, obtained by analysis of elements contained within rocks, have only recently become available. Therefore, dates or descriptions of sequences of events should be regarded with some caution until better data become available, fossils of organisms bodies are usually the most informative type of evidence. Fossilization is an event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence, the record is very incomplete, increasingly so as earlier times are considered. Despite this, they are adequate to illustrate the broader patterns of lifes history. Also, biases exist in the record, different environments are more favourable to the preservation of different types of organism or parts of organisms
12.
Acid
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An acid is a molecule or ion capable of donating a hydron, or, alternatively, capable of forming a covalent bond with an electron pair. The first category of acids is the donors or Brønsted acids. In the special case of solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents, acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals to form salts. The word acid is derived from the Latin acidus/acēre meaning sour, an aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as acid, while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic, common aqueous acids include hydrochloric acid, acetic acid, sulfuric acid, and citric acid. As these examples show, acids can be solutions or pure substances, strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid. The second category of acids are Lewis acids, which form a covalent bond with an electron pair, however, hydrogen chloride, acetic acid, and most other Brønsted-Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted-Lowry acids, in modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid. Modern definitions are concerned with the chemical reactions common to all acids. Most acids encountered in life are aqueous solutions, or can be dissolved in water, so the Arrhenius. The Brønsted-Lowry definition is the most widely used definition, unless otherwise specified, hydronium ions are acids according to all three definitions. Interestingly, although alcohols and amines can be Brønsted-Lowry acids, they can function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms. The Swedish chemist Svante Arrhenius attributed the properties of acidity to hydrogen ions or protons in 1884, an Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in the water. Thus, an Arrhenius acid can also be described as a substance that increases the concentration of ions when added to water. Examples include molecular substances such as HCl and acetic acid, an Arrhenius base, on the other hand, is a substance which increases the concentration of hydroxide ions when dissolved in water. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, in an acidic solution, the concentration of hydronium ions is greater than 10−7 moles per liter
13.
Carbonate
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In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−3. The name may mean an ester of carbonic acid, an organic compound containing the carbonate group C2. In geology and mineralogy, the term carbonate can refer both to carbonate minerals and carbonate rock, and both are dominated by the ion, CO2−3. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated sedimentary rock, sodium carbonate and potassium carbonate have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, e. g. in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, the carbonate ion is the simplest oxocarbon anion. It consists of one carbon atom surrounded by three oxygen atoms, in a planar arrangement, with D3h molecular symmetry. It has a mass of 60.01 g/mol and carries a total formal charge of −2. It is the base of the hydrogen carbonate ion, HCO−3. The Lewis structure of the ion has two single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen. This structure is incompatible with the symmetry of the ion. This process is called calcination, after calx, the Latin name of quicklime or calcium oxide, CaO, exceptions include lithium, sodium, potassium and ammonium carbonates, as well as many uranium carbonates. In aqueous solution, carbonate, bicarbonate, carbon dioxide, in strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion is prevalent. In more acid conditions, aqueous carbon dioxide, CO2, is the main form, thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid. Carbonated water is formed by dissolving CO2 in water under pressure, in living systems an enzyme, carbonic anhydrase, speeds the interconversion of CO2 and carbonic acid. Although the carbonate salts of most metals are insoluble in water, in solution this equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid changes consonant to changing temperature and pressure conditions. In the case of ions with insoluble carbonates, e. g. CaCO3. This is an explanation for the buildup of scale inside pipes caused by hard water, in organic chemistry a carbonate can also refer to a functional group within a larger molecule that contains a carbon atom bound to three oxygen atoms, one of which is double bonded. These compounds are known as organocarbonates or carbonate esters, and have the general formula ROCOOR′
14.
Animal
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Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
15.
Chlorophyta
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Chlorophyta is a division of green algae, informally called chlorophytes. The name is used in two different senses, so care is needed to determine the use by a particular author. In newer classifications, it refers to one of the two clades making up the Viridiplantae, which are the chlorophytes and the streptophytes, the clade Streptophyta consists of two divisions, the Charophyta and the Embryophyta. In this sense the Chlorophyta includes only about 4,300 species, like the land plants, green algae contain chlorophyll a and chlorophyll b and store food as starch in their plastids. The division contains both unicellular and multicellular species, some conduct sexual reproduction, which is oogamous or isogamous. All members of the clade have motile flagellated swimming cells, while most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of land environments. For example, Chlamydomonas nivalis, which causes Watermelon snow, lives on summer alpine snowfields, others, such as Trentepohlia species, live attached to rocks or woody parts of trees. Monostroma kuroshiensis, a green alga cultivated worldwide and most expensive among green algae. Some members of the Chlorophyta form symbiotic relationships with protozoa, sponges, others form symbiotic relationships with fungi to form lichens. Species of Chlorophyta are common inhabitants of marine, freshwater and terrestrial environments, several species have adapted to specialised and extreme environments, such as deserts, arctic environments, hypersaline habitats, marine deep waters and deep-sea hydrothermal vents. Some groups, such as the Trentepohliales are exclusively found on land, several species of Chlorophyta live in symbiosis with a diverse range of eukaryotes, including fungi, ciliates, forams, cnidarians and molluscs. Some species of Chlorophyta are heterotrophic, either free-living or parasitic, two common species of the heterotrophic green alga Prototheca are pathogenic and can cause the disease protothecosis in humans and animals. A newer proposed classification follows Leliaert et al.2011 and modified with Silar 2016 for the green algae clades, simplified phylogeny of the Chlorophyta, according to Leliaert et al. Note that many previously classified in Chlorophyta are placed here in Streptophyta. Class Prasinophyceae T. A. Chr. ex Ø, moestrup & J. Throndsen Class Chlorophyceae Wille Class Trebouxiophyceae T. Friedl Class Ulvophyceae K. R. Mattox & K. D. Chlorophyceae Order 1. Ulvaceae Family 2 Schizomeridaceae Order 5, charophyceae Order Charales Family Characeae Burrows, E. M.1991. ISBN 0-565-00981-8 Lewis, L. A. McCourt, R. M. Green algae, structure, Reproduction and Evolution in Selected Genera
16.
Dinoflagellate
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The dinoflagellates are a large group of flagellate eukaryotes that constitute the phylum Dinoflagellata. Most are marine plankton, but they are common in freshwater habitats and their populations are distributed depending on temperature, salinity, or depth. Many dinoflagellates are known to be photosynthetic, but a fraction of these are in fact mixotrophic. In terms of number of species, dinoflagellates form one of the largest groups of marine eukaryotes, some species are endosymbionts of marine animals and play an important part in the biology of coral reefs. Other dinoflagellates are unpigmented predators on other protozoa, and a few forms are parasitic, some dinoflagellates produce resting stages, called dinoflagellate cysts or dinocysts, as part of their lifecycles. Dinoflagellates are considered to be protists, with their own division, about 1,555 species of free-living marine dinoflagellates are currently described. Another estimate suggests about 2,000 living species, of more than 1,700 are marine. The latest estimates suggest a total of 2,294 living dinoflagellate species, a bloom of certain dinoflagellates can result in a visible coloration of the water colloquially known as red tide, which can cause shellfish poisoning if humans consume contaminated shellfish. In 1753, the first modern dinoflagellates were described by Henry Baker as Animalcules which cause the Sparkling Light in Sea Water, the term derives from the Greek word δῖνος, meaning whirling, and Latin flagellum, a diminutive term for a whip or scourge. These same dinoflagellates were first defined by Otto Bütschli in 1885 as the flagellate order Dinoflagellida, botanists treated them as a division of algae, named Pyrrophyta or Pyrrhophyta after the bioluminescent forms, or Dinophyta. At various times, the cryptomonads, ebriids, and ellobiopsids have been included here, dinoflagellates have a known ability to transform from noncyst to cyst-forming strategies, which makes recreating their evolutionary history extremely difficult. Dinoflagellates are protists which have been classified using both the International Code of Botanical Nomenclature and the International Code of Zoological Nomenclature, about half of living dinoflagellate species are autotrophs possessing chloroplasts and half are nonphotosynthesising heterotrophs. Most dinoflagellates have a dinokaryon, described below, dinoflagellates with a dinokaryon are classified under Dinokaryota, while dinoflagellates without a dinokaryon are classified under Syndiniales. This group, however, does contain typically eukaryotic organelles, such as Golgi bodies, mitochondria, jakob Schiller provided a description of all the species, both marine and freshwater, known at that time. Later, Alain Sournia listed the new taxonomic entries published after Schiller, Sournia gave descriptions and illustrations of the marine genera of dinoflagellates, excluding information at the species level. The latest index is written by Gómez, english-language taxonomic monographs covering large numbers of species are published for the Gulf of Mexico, the Indian Ocean, the British Isles, the Mediterranean and the North Sea. The main source for identification of freshwater dinoflagellates is the Süsswasser Flora, calcofluor-white can be used to stain thecal plates in armoured dinoflagellates. Dinoflagellates are unicellular and possess two dissimilar flagella arising from the ventral cell side and they have a ribbon-like transverse flagellum with multiple waves that beats to the cells left, and a more conventional one, the longitudinal flagellum, that beats posteriorly
17.
Algae
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Algae is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to forms, such as the giant kelp. Most are aquatic and autotrophic and lack many of the cell and tissue types, such as stomata, xylem, and phloem. No definition of algae is generally accepted, one definition is that algae have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells. Some authors exclude all prokaryotes thus do not consider cyanobacteria as algae, Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria, diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, and the roots, leaves, and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago, the singular alga is the Latin word for seaweed and retains that meaning in English. Although some speculate that it is related to Latin algēre, be cold, a more likely source is alliga, binding, entwining. The Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it, the Latinization, fūcus, meant primarily the cosmetic rouge. It could be any color, black, red, green, accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name Fucus appears in a number of taxa, most algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and presumably represent reduced endosymbiotic cyanobacteria, however, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three groups of algae. Their lineage relationships are shown in the figure in the upper right, many of these groups contain some members that are no longer photosynthetic
18.
Form classification
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Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty, the goal of science is to form taxa to biological taxa whose affinity is known. Form taxa are groupings that are based on common overall forms, early attempts at classification of labyrinthodonts was based on skull shape. The amount of convergent evolution in the groups lead to a number of polyphyletic taxa. Such groups are united by a mode of life, often one that is generalist. Ediacaran biota — whether they are the precursors of the Cambrian explosion of the fossil record, other examples include the seabirds and the Graculavidae. A parataxon, or sciotaxon, is a based on incomplete data, for instance. It reflects a paucity of data that makes biological classification impossible, a later term morphotaxa also allows for differences in preservational state. These three terms have been replaced as of 2011 by provisions for fossil-taxa that are similar to the provisions for other types of plants. Names given to organ genera could only be applied to the organs in question, fossil-taxon names can cover several parts of an organism, or several preservational states, but do not compete for priority with any names for the same organism that are based on a non-fossil type. Well-known form taxa of this kind include ducks, fish, reptiles and worms
19.
Taxon
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In biology, a taxon is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is known by a particular name and given a particular ranking, especially if. It is not uncommon, however, for taxonomists to remain at odds over what belongs to a taxon, if a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping. Many modern systematists, such as advocates of phylogenetic nomenclature, use cladistic methods that require taxa to be monophyletic and their basic unit, therefore, is the clade rather than the taxon. Similarly, among those contemporary taxonomists working with the traditional Linnean nomenclature, an example of a well-established taxon that is not also a clade is the class Reptilia, the reptiles, birds are descendants of reptiles but are not included in the Reptilia. The term taxon was first used in 1926 by Adolf Meyer-Abich for animal groups, for plants, it was proposed by Herman Johannes Lam in 1948, and it was adopted at the VII International Botanical Congress, held in 1950. The Glossary of the International Code of Zoological Nomenclature defines a taxon, a taxon encompasses all included taxa of lower rank and individual organisms. A taxon can be assigned a rank, usually when it is given a formal name. Phylum applies formally to any domain, but traditionally it was always used for animals, whereas Division was traditionally often used for plants, fungi. A prefix is used to indicate a ranking of lesser importance, the prefix super- indicates a rank above, the prefix sub- indicates a rank below. In zoology the prefix infra- indicates a rank below sub-, for instance, among the additional ranks of class are superclass, subclass and infraclass. Rank is relative, and restricted to a particular systematic schema, for example, liverworts have been grouped, in various systems of classification, as a family, order, class, or division. Many cladists do not see any need to depart from traditional nomenclature as governed by the ICZN, ICN, etc
20.
Cambrian
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The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya and its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, as a result, our understanding of the Cambrian biology surpasses that of some later periods. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia, the seas were relatively warm, and polar ice was absent for much of the period. The United States Federal Geographic Data Committee uses a barred capital C ⟨Є⟩ character similar to the capital letter Ukrainian Ye ⟨Є⟩ to represent the Cambrian Period, the proper Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR. Despite the long recognition of its distinction from younger Ordovician Period rocks and older Supereon Precambrian rocks, the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period, the Cambrian is divided into four epochs and ten ages. Currently only two series and five stages are named and have a GSSP, because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian, Middle Cambrian and Furongian, rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian, each of the local epochs is divided into several stages. The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago, the lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier and this formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the used to obtain this number are now considered to be unsuitable. A more precise date using modern radiometric dating yield a date of 541 ±0.3 million years ago, most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian, the sea levels fluctuated somewhat, suggesting there were ice ages, associated with pulses of expansion and contraction of a south polar ice cap. In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into a epicontinental sea, the Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents
21.
Extinction event
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An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a change in the diversity. It occurs when the rate of extinction increases with respect to the rate of speciation, Extinction occurs at an uneven rate. Based on the record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. Marine fossils are used to measure extinction rates because of their superior fossil record. The Great Oxygenation Event was probably the first major extinction event, since the Cambrian explosion five further major mass extinctions have significantly exceeded the background extinction rate. In addition to the five mass extinctions, there are numerous minor ones as well. Mass extinctions seem to be a mainly Phanerozoic phenomenon, with extinction rates low before large complex organisms arose, estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the chosen for describing an extinction event as major. In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five mass extinctions, the Big Five cannot be so clearly defined, but rather appear to represent the largest of a relatively smooth continuum of extinction events. Cretaceous–Paleogene extinction event,66 Ma at the Cretaceous -Paleogene transition interval, the event formerly called the Cretaceous-Tertiary or K–T extinction or K-T boundary is now officially named the Cretaceous–Paleogene extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct, in the seas all the ammonites, plesiosaurs and mosasaurs disappeared and the percentage of sessile animals was reduced to about 33%. All non-avian dinosaurs became extinct during that time, the boundary event was severe with a significant amount of variability in the rate of extinction between and among different clades. Mammals and birds, the latter descended from dinosaurs, emerged as dominant large land animals. Triassic–Jurassic extinction event,201.3 Ma at the Triassic-Jurassic transition, about 23% of all families, 48% of all genera and 70% to 75% of all species became extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the amphibians were eliminated. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments, the Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia. Permian–Triassic extinction event,252 Ma at the Permian-Triassic transition, Earths largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species
22.
Permian
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The Permian is a geologic period and system which spans 46.7 million years from the end of the Carboniferous Period 298.9 million years ago, to the beginning of the Triassic Period 252.2 Mya. It is the last period of the Paleozoic Era, the following Triassic Period belongs to the Mesozoic Era, the concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm. The Permian witnessed the diversification of the early amniotes into the groups of the mammals, turtles, lepidosaurs. The world at the time was dominated by two known as Pangaea and Siberia, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior, amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. The Permian ended with the Permian–Triassic extinction event, the largest mass extinction in Earths history, in which nearly 90% of marine species and it would take well into the Triassic for life to recover from this catastrophe. Recovery from the Permian-Triassic extinction event was protracted, on land, the term Permian was introduced into geology in 1841 by Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil, the region now lies in the Perm Krai of Russia. This could have in part caused the extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms. During the Permian, all the Earths major landmasses were collected into a supercontinent known as Pangaea. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, a new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmass interiors experience climates with extreme variations of heat and cold, deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a cover, over plants such as ferns that disperse spores in a wetter environment. The first modern trees appeared in the Permian, the climate in the Permian was quite varied. At the start of the Permian, the Earth was still in an Ice Age, glaciers receded around the mid-Permian period as the climate gradually warmed, drying the continents interiors. In the late Permian period, the drying continued although the temperature cycled between warm and cool cycles, Permian marine deposits are rich in fossil mollusks, echinoderms, and brachiopods. By the close of the Permian, trilobites and a host of other groups became extinct. Terrestrial life in the Permian included diverse plants, fungi, arthropods, the period saw a massive desert covering the interior of Pangaea
23.
Prokaryote
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A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek πρό before and καρυόν nut or kernel, prokaryotes can be divided into two domains, Archaea and bacteria. In contrast, species with nuclei and organelles are placed in the domain Eukaryota, in the prokaryotes, all the intracellular water-soluble components are located together in the cytoplasm enclosed by the cell membrane, rather than in separate cellular compartments. Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells, some prokaryotes, such as cyanobacteria may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles, molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species. Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus, the division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization. Distinctive types of prokaryotes include extremophiles and methanogens, these are common in extreme environments. Prokaryotes have a cytoskeleton, albeit more primitive than that of the eukaryotes. At least some also contain intracellular structures that can be seen as primitive organelles. Membranous organelles are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, in addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles. Most prokaryotes are between 1 µm and 10 µm, but they can vary in size from 0.2 µm to 750 µm, Bacteria and archaea reproduce through asexual reproduction, usually by binary fission. DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has mainly studied in bacteria. In bacteria, gene transfer occurs by three processes and these are bacterial virus -mediated transduction, plasmid-mediated conjugation, and natural transformation. Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, the transfer of bacterial DNA is under the control of the bacteriophage’s genes rather than bacterial genes. Conjugation in the well-studied E. coli system is controlled by plasmid genes, infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA also appears to be a process rather than a bacterial adaptation. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium, for a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called competence. About 40 genes are required in Bacillus subtilis for the development of competence, the length of DNA transferred during B. subtilis transformation can be as much as a third to the whole chromosome
24.
Proterozoic
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The Proterozoic is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means life, the Greek root protero-, means former, earlier and zoic-, means animal. The Proterozoic Eon extended from 2500 Ma to 541 Ma, and is the most recent part of the Precambrian Supereon and it is subdivided into three geologic eras, the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The geologic record of the Proterozoic Eon is more complete than that for the preceding Archean Eon, studies of these rocks have shown that the eon continued the massive continental accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern mountain building activity, there is evidence that the first known glaciations occurred during the Proterozoic. One of the most important events of the Proterozoic was the accumulation of oxygen in the Earths atmosphere, until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. The Banded iron formations, which provide most of the iron ore, are one mark of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans had all been oxidized, red beds, which are colored by hematite, indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks, the Proterozoic Eon was a very tectonically active period in the Earth’s history. The late Archean Eon to Early Proterozoic Eon corresponds to a period of increasing crustal recycling, suggesting subduction, evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga. The appearance of eclogites, which metamorphic rocks created by pressure, are explained using a model that incorporates subduction. As a result of remelting of basaltic oceanic crust due to subduction, the long-term tectonic stability of those cratons is why we find continental crust ranging up to a few billion years in age. It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, studies by Condie 2000 and Rino et al.2004 suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it was determined there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period, evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents. Paleomagnetic and geochronological dating mechanisms have allowed the deciphering of Precambrian Supereon tectonics and it is known that tectonic processes of the Proterozoic Eon resemble greatly the evidence of tectonic activity, such as orogenic belts or ophiolite complexes, we see today. Hence, most geologists would conclude that the Earth was active at that time and it is also commonly accepted that during the Precambrian, the Earth went through several supercontinent breakup and rebuilding cycles. In the late Proterozoic, the dominant supercontinent was Rodinia and it consisted of a series of continents attached to a central craton that forms the core of the North American Continent called Laurentia
25.
Hydrofluoric acid
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Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a precursor to almost all compounds, including pharmaceuticals such as fluoxetine, diverse materials such as PTFE. It is a solution that is highly corrosive, capable of dissolving many materials. Its ability to dissolve glass has been known since the 17th century, because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic containers. Hydrogen fluoride gas is a poison that may immediately and permanently damage lungs. Aqueous hydrofluoric acid is a contact-poison with the potential for deep, initially painless burns, by interfering with body calcium metabolism, the concentrated acid may also cause systemic toxicity and eventual cardiac arrest and fatality, after contact with as little as 160 cm2 of skin. Hydrofluoric acid is classified as an acid because of its lower dissociation constant compared to the strong acids. Hydrofluoric acid is produced by treatment of the mineral fluorite with concentrated sulfuric acid, apatite sources typically contain a few percent of fluoroapatite, acid digestion of which releases a gaseous stream consisting of sulfur dioxide, water, and HF, as well as particulates. After separation from the solids, the gases are treated with sulfuric acid, owing to the corrosive nature of HF, its production is accompanied by the dissolution of silicate minerals, and, in this way, significant amounts of fluorosilicic acid are generated. Hydrofluoric acid has a variety of uses in industry and research and it is used as a starting material or intermediate in industrial chemistry, mining, refining, glass finishing, silicon chip manufacturing, and in cleaning. In a standard oil refinery known as alkylation, isobutane is alkylated with low-molecular-weight alkenes in the presence of the strong acid catalyst derived from hydrofluoric acid. The catalyst protonates the alkenes to produce reactive carbocations, which alkylate isobutane, the reaction is carried out at mild temperatures in a two-phase reaction. The principal use of acid is in organofluorine chemistry. Many organofluorine compounds are prepared using HF as the source, including Teflon, fluoropolymers, fluorocarbons. Most high-volume inorganic fluoride compounds are prepared from hydrofluoric acid, foremost are Na3AlF6, cryolite, and AlF3, aluminium trifluoride. A molten mixture of these serves as a high-temperature solvent for the production of metallic aluminium. Given concerns about fluorides in the environment, alternative technologies are being sought, other inorganic fluorides prepared from hydrofluoric acid include sodium fluoride and uranium hexafluoride. In metalworking, hydrofluoric acid is used as an agent to remove oxides and other impurities from stainless
26.
Palaeozoic
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The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, from 541 to 252.17 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous. The Paleozoic comes after the Neoproterozoic era of the Proterozoic and is followed by the Mesozoic, the Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earths history, known as the Cambrian explosion, fish, arthropods, amphibians, anapsids, synapsids, euryapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, 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, large, sophisticated diapsids and synapsids were dominant, 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 margins, and flooding and draining of shallow seas between. At its start, the supercontinent Pannotia broke up, paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwana formed or was forming, by mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. There are six periods in the Paleozoic Era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, 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 period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, the Ordovician spanned from 485 million years to 443 million years ago. The Ordovician is a time in Earths history in many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovican, Gondwana was at the pole, early North America had collided with Europe. Glaciation of Africa resulted in a drop in sea level
27.
Paleozoic
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The Paleozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, from 541 to 252.17 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous. The Paleozoic comes after the Neoproterozoic era of the Proterozoic and is followed by the Mesozoic, the Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earths history, known as the Cambrian explosion, fish, arthropods, amphibians, anapsids, synapsids, euryapsids and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, 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, large, sophisticated diapsids and synapsids were dominant, 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 margins, and flooding and draining of shallow seas between. At its start, the supercontinent Pannotia broke up, paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwana formed or was forming, by mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. There are six periods in the Paleozoic Era, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, 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 period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, the Ordovician spanned from 485 million years to 443 million years ago. The Ordovician is a time in Earths history in many of the biological classes still prevalent today evolved, such as primitive fish, cephalopods. The most common forms of life, however, were trilobites, snails, more importantly, the first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovican, Gondwana was at the pole, early North America had collided with Europe. Glaciation of Africa resulted in a drop in sea level
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Greek (language)
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Greek is an independent branch of the Indo-European family of languages, native to Greece and other parts of the Eastern Mediterranean. It has the longest documented history of any living language, spanning 34 centuries of written records and its writing system has been the Greek alphabet for the major part of its history, other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic and many other writing systems. Together with the Latin texts and traditions of the Roman world, during antiquity, Greek was a widely spoken lingua franca in the Mediterranean world and many places beyond. It would eventually become the official parlance of the Byzantine Empire, the language is spoken by at least 13.2 million people today in Greece, Cyprus, Italy, Albania, Turkey, and the Greek diaspora. Greek roots are used to coin new words for other languages, Greek. Greek has been spoken in the Balkan peninsula since around the 3rd millennium BC, the earliest written evidence is a Linear B clay tablet found in Messenia that dates to between 1450 and 1350 BC, making Greek the worlds oldest recorded living language. Among the Indo-European languages, its date of earliest written attestation is matched only by the now extinct Anatolian languages, the Greek language is conventionally divided into the following periods, Proto-Greek, the unrecorded but assumed last ancestor of all known varieties of Greek. The unity of Proto-Greek would have ended as Hellenic migrants entered the Greek peninsula sometime in the Neolithic era or the Bronze Age, Mycenaean Greek, the language of the Mycenaean civilisation. It is recorded in the Linear B script on tablets dating from the 15th century BC onwards, Ancient Greek, in its various dialects, the language of the Archaic and Classical periods of the ancient Greek civilisation. It was widely known throughout the Roman Empire, after the Roman conquest of Greece, an unofficial bilingualism of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. The origin of Christianity can also be traced through Koine Greek, Medieval Greek, also known as Byzantine Greek, the continuation of Koine Greek in Byzantine Greece, up to the demise of the Byzantine Empire in the 15th century. Much of the written Greek that was used as the language of the Byzantine Empire was an eclectic middle-ground variety based on the tradition of written Koine. Modern Greek, Stemming from Medieval Greek, Modern Greek usages can be traced in the Byzantine period and it is the language used by the modern Greeks, and, apart from Standard Modern Greek, there are several dialects of it. In the modern era, the Greek language entered a state of diglossia, the historical unity and continuing identity between the various stages of the Greek language is often emphasised. Greek speakers today still tend to regard literary works of ancient Greek as part of their own rather than a foreign language and it is also often stated that the historical changes have been relatively slight compared with some other languages. According to one estimation, Homeric Greek is probably closer to demotic than 12-century Middle English is to modern spoken English, Greek is spoken by about 13 million people, mainly in Greece, Albania and Cyprus, but also worldwide by the large Greek diaspora. Greek is the language of Greece, where it is spoken by almost the entire population
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Vernanimalcula
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Vernanimalcula guizhouena is an acritarch dating from 600 to 580 million years ago, it was between 0.1 and 0.2 mm across. Vernanimalcula means small spring animal, referring to its appearance in the record at the end of the Marinoan Glaciation. The Vernanimalcula fossils were discovered in the Doushantuo Formation in China and this formation is a Konservat-Lagerstätte, one of the rare places where soft body parts and very fine details are preserved in the fossil record. The appearance of Vernanimalcula so early in the record was believed to have had important implications if it were really bilaterian. The description of Vernanimalcula as bilaterian has been strongly challenged, chen et al. initially defended their interpretation of Vernanimalcula against the claims of Bengtson and Budd. Petryshyn et al. examined additional fossils resembling Vernanimalcula and concluded that the fossils are likely biogenic in nature
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PubMed Identifier
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PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval, from 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home-, the PubMed system was offered free to the public in June 1997, when MEDLINE searches via the Web were demonstrated, in a ceremony, by Vice President Al Gore. Information about the journals indexed in MEDLINE, and available through PubMed, is found in the NLM Catalog. As of 5 January 2017, PubMed has more than 26.8 million records going back to 1966, selectively to the year 1865, and very selectively to 1809, about 500,000 new records are added each year. As of the date,13.1 million of PubMeds records are listed with their abstracts. In 2016, NLM changed the system so that publishers will be able to directly correct typos. Simple searches on PubMed can be carried out by entering key aspects of a subject into PubMeds search window, when a journal article is indexed, numerous article parameters are extracted and stored as structured information. Such parameters are, Article Type, Secondary identifiers, Language, publication type parameter enables many special features. As these clinical girish can generate small sets of robust studies with considerable precision, since July 2005, the MEDLINE article indexing process extracts important identifiers from the article abstract and puts those in a field called Secondary Identifier. The secondary identifier field is to store numbers to various databases of molecular sequence data, gene expression or chemical compounds. For clinical trials, PubMed extracts trial IDs for the two largest trial registries, ClinicalTrials. gov and the International Standard Randomized Controlled Trial Number Register, a reference which is judged particularly relevant can be marked and related articles can be identified. If relevant, several studies can be selected and related articles to all of them can be generated using the Find related data option, the related articles are then listed in order of relatedness. To create these lists of related articles, PubMed compares words from the title and abstract of each citation, as well as the MeSH headings assigned, using a powerful word-weighted algorithm. The related articles function has been judged to be so precise that some researchers suggest it can be used instead of a full search, a strong feature of PubMed is its ability to automatically link to MeSH terms and subheadings. Examples would be, bad breath links to halitosis, heart attack to myocardial infarction, where appropriate, these MeSH terms are automatically expanded, that is, include more specific terms. Terms like nursing are automatically linked to Nursing or Nursing and this important feature makes PubMed searches automatically more sensitive and avoids false-negative hits by compensating for the diversity of medical terminology. The My NCBI area can be accessed from any computer with web-access, an earlier version of My NCBI was called PubMed Cubby
