Atlantic sailfish
The Atlantic sailfish is a species of marine fish in the family Istiophoridae of the order Perciformes. It is found in the Atlantic Oceans and the Caribbean Sea, except for large areas of the central North Atlantic and the central South Atlantic, from the surface to depths of 200 m; the Atlantic sailfish is related to the marlin. Tests in the 1920s estimated that the Atlantic sailfish was capable of short sprints of up to 111 kilometres per hour. More recent studies suggest sailfish do not exceed swimming speeds of 36 km/h. Atlantic sailfish hunt schooling fish, such as sardines and mackerel although they feed on crustaceans and cephalopods; the Atlantic sailfish is a metallic blue fish with a large sail-like dorsal fin and a long and pointed bill-like snout. It is dark bluish-black on the upperparts and lighter on the sides, with about twenty bluish horizontal bars along the flanks; the tail fin is forked. The fins are bluish-black and the front dorsal fin is speckled with small black spots; the bases of the anal fins are pale.
The length of this fish is up to 3.15 m and the maximum published weight is 58.1 kg. In previous studies, sailfish hunting schools of sardines rely upon stealth and quick slashing or tapping with the rostrum in order to temporarily immobilize prey and facilitate capture in small prey; the adaptive advantage of the bill is debated and many different functions have been suggested. The bill has been hypothesized to increase the hydrodynamic qualities of the fish and to ward off predators. However, it has been well documented; the Atlantic sailfish is a pelagic fish of temperate waters in the Atlantic Ocean. It ranges from 40°N in the northwestern Atlantic to 40°S in the southwestern Atlantic, 50°N in the northeastern Atlantic to 32°S in the southeastern Atlantic, it is a migratory moves about the open ocean and into the Mediterranean Sea. Its depth range is from warm surface waters down to about 200 m; some authorities only recognise a single species of sailfish, Istiophorus platypterus, with I. albicans being treated as a synonym for I. platyperus.
"Istiophorus albicans". Integrated Taxonomic Information System. Retrieved 6 June 2006. Video clips from the BBC
Cambrian
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. Its subdivisions, its base, are somewhat in flux; the period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells; as a result, our understanding of the Cambrian biology surpasses that of some periods. The Cambrian marked a profound change in life on Earth. Complex, multicellular organisms became more common in the millions of years preceding the Cambrian, but it was not until this period that mineralized—hence fossilized—organisms became common; the rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates. Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were 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 warm, polar ice was absent for much of the period. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified; the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia and Newfoundland, in the western USA.
The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, in Spain. The Cambrian Period was followed by the Ordovician Period; the Cambrian is divided into ten ages. Only three series and six stages are named and have a GSSP; because the international stratigraphic subdivision is not yet complete, many local subdivisions are still used. In some of these subdivisions the Cambrian is divided into three series with locally differing names – the Early Cambrian, Middle Cambrian and Furongian. Rocks of these epochs are referred to as belonging to Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian; each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance: *Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was held to represent the first appearance of complex life, represented by trilobites; the recognition of small shelly fossils before the first trilobites, Ediacara biota earlier, led to calls for a more defined base to the Cambrian period. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, it is the T. pedum ichnofossil assemblage, now formally used to correlate the base of the Cambrian. 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 gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate.
A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago. The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, to the disappearance of distinctive Ediacaran fossils. There are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata — which w
Marlin
A marlin is a fish from the family Istiophoridae, which includes about 10 species. It has an elongated body, a spear-like snout or bill, a long, rigid dorsal fin which extends forward to form a crest, its common name is thought to derive from its resemblance to a sailor's marlinspike. More so than their close relatives, the scombrids, marlins are fast swimmers, reaching speeds of about 80 km/h; the larger species include the Atlantic blue marlin, Makaira nigricans, which can reach 5 m in length and 818 kg in weight and the black marlin, Istiompax indica, which can reach in excess of 5 m in length and 670 kg in weight. They are popular sporting fish in tropical areas; the marlins are perciform fish, most related to the swordfish and Scombridae. In the Nobel Prize-winning author Ernest Hemingway's 1952 novel The Old Man and the Sea, the central character of the work is an aged Cuban fisherman who, after 84 days without success on the water, heads out to sea to break his run of bad luck. On the 85th day, the old fisherman, hooks a resolute marlin.
Frederick Forsyth's story "The Emperor", in the collection No Comebacks, tells of a bank manager named Murgatroyd, who catches a marlin and is acknowledged by the islanders of Mauritius as a master fisherman. Marlin fishing Sailfish Froese and Daniel Pauly, eds.. "Istiophoridae" in FishBase. November 2005 version. Sepkoski, Jack. "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23. Retrieved 2011-05-19. "'Ghost Fish' Revelation May Alter Marlin's Status" from National Public Radio
Bernard Germain de Lacépède
Bernard-Germain-Étienne de La Ville-sur-Illon, comte de Lacépède or La Cépède was a French naturalist and an active freemason. He is known for his contribution to the Histoire Naturelle. Lacépède was born at Agen in Guienne, his education was conducted by his father, the early perusal of Buffon's Natural History awakened his interest in that branch of study, which absorbed his chief attention. His leisure he devoted to music, in which, besides becoming a good performer on the piano and organ, he acquired considerable mastery of composition, two of his operas meeting with the high approval of Gluck. Meantime he wrote two treatises, Essai sur l'électricité and Physique générale et particulaire, which gained him the friendship of Buffon, who in 1785 appointed him subdemonstrator in the Jardin du Roi, proposed that he continue Buffon's Histoire naturelle; this continuation was published under the titles Histoire naturelle des quadrupèdes ovipares et des serpents. Tome premier and Histoire naturelle des serpents.
Tome second. After the French Revolution Lacépède became a member of the Legislative Assembly, but during the Reign of Terror he left Paris, his life having become endangered by his disapproval of the massacres; when the Jardin du Roi was reorganised as the Jardin des Plantes, Lacépède was appointed to the chair allocated to the study of reptiles and fishes. In 1798, he published the first volume of Histoire naturelle des poissons, the fifth volume appearing in 1803, in 1804 appeared his Histoire des cétacées. From this period until his death the part he took in politics prevented him making any further contribution of importance to science. In 1799, he became a senator, in 1801 president of the senate, in 1803 grand chancellor of the Legion of Honor, in 1804 minister of state, at the Bourbon Restoration in 1819 he was created a peer of France, he died at Épinay-sur-Seine. During the latter part of his life he wrote Histoire générale physique et civile de l'Europe, published posthumously in 18 volumes, 1826.
He was elected a member of the Institute of France in 1796, a Fellow of the Royal Society in 1806 and a foreign member of the Royal Swedish Academy of Sciences in 1812. Lacépède was initiated into freemasonry at 22 years old at Les Neuf Sœurs lodge in Paris, by Jérôme Lalande the worshipfull master himself, who wanted a naturalist for his prestigious lodge. In 178.5 millionépède created his own lodge: "Les Frères Initiés". After the Revolution, he helped Cambacérès to rebuild a French freemasonry submitted to the Emperor, joined "Saint-Napoléon" lodge where General Kellermann was worshipfull master, he finished his masonic life as dignitary of the Suprême Conseil de France. Lacepede Bay in South Australia, the Lacepede Islands off the northern coast of Western Australia, are named after him, as is the Rue Lacepede near the Jardin des Plantes. A species of gecko endemic to Mauritius, Phelsuma cepediana, is named in his honour. Lacépède was an early evolutionary thinker, he argued for the transmutation of species.
He believed that species change over time and may go extinct from geological cataclysms or become "metamorphosed" into new species. In his book Histoire naturelle des poissons, he wrote: "The species can undergo such a large number of modifications in its forms and qualities, that without losing its vital capacity, it may be, by its latest conformation and properties, farther removed from its original state than from a different species: it is in that case metamorphosed into a new species." Les ages de la nature et histoire de l'espèce humaine. Paris 1830 p.m. Histoire naturelle de l'homme. Pitois-Le Vrault, Paris 1827 p.m. Histoire générale, physique et civile de l'Europe. Cellot, Delaunay-Vallée & de Mat, Paris, Brüssel 1826 p.m. Histoire naturelle des quadrupèdes ovipares, poissons et cétacées. Eymery, Paris 1825. Histoire naturelle des cétacées. Plassan, Paris 1804. Notice historique sur la vie et les ouvrages de Dolomieu. Bossange, Paris 1802. La menagerie du Museum national d'histoire naturelle.
Miger, Paris 1801–04. Discours d'ouverture et de clôture. Plassan, Paris 1801. Discours d'ouverture et de clôture. Plassan, Paris 1799. Histoire naturelle des poissons. Plassan, Paris 1798–1803. Discours d'ouverture et de clôture du cours d'histoire naturelle des animaux vertébrés et a sang rouge. Plassan, Paris 1798. Discours d'ouverture du Cours d'histoire naturelle. Paris 1797. Histoire naturelle des serpents. Tome second. De Thou, Paris 1789. Histoire naturelle des quadrupèdes ovipares et des serpens. Tome premier. De Thou, Paris 1788. Vie de Buffon. Maradan, Amsterdam 1788. La poétique de la musique. Paris 1785. Physique générale. Paris 1782–84. Essai sur l'électricité naturelle et artificielle. Paris 1781. Schmitt, Stéphane. "Lacepède’s syncretic contribution to the debates on natural history in France around 1800". Journal of the History of Biology 43: 429-457. Cuvier, Georges. Éloges historiques de MM. de Saussure, Hauy, de Lacépède et Cavendish. Münster: Theissing.. Saloman, Ora Frishberg. Aspects of "Gluckian" operatic practice in France.
Ann Arbor. Roule, Louis. Lacépède, professeur au Muséum, premier grand chancellier de la Légion d'honneur, et la sociologie humanitaire selon la nature. Paris: Flammarion.. Internet Archive Works by Lacepede Lacépède Histoire naturelle 2 vol. – Linda Hall Library
Miocene
The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago. The Miocene was named by Charles Lyell; the Miocene is followed by the Pliocene. As the earth went from the Oligocene through the Miocene and into the Pliocene, the climate cooled towards a series of ice ages; the Miocene boundaries are not marked by a single distinct global event but consist rather of regionally defined boundaries between the warmer Oligocene and the cooler Pliocene Epoch. The Apes first evolved and diversified during the early Miocene, becoming widespread in the Old World. By the end of this epoch and the start of the following one, the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path during the final Messinian stage of the Miocene; as in the Oligocene before it, grasslands continued to forests to dwindle in extent. In the seas of the Miocene, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems.
The plants and animals of the Miocene were recognizably modern. Mammals and birds were well-established. Whales and kelp spread; the Miocene is of particular interest to geologists and palaeoclimatologists as major phases of the geology of the Himalaya occurred during the Miocene, affecting monsoonal patterns in Asia, which were interlinked with glacial periods in the northern hemisphere. The Miocene faunal stages from youngest to oldest are named according to the International Commission on Stratigraphy: Regionally, other systems are used, based on characteristic land mammals. Of the modern geologic features, only the land bridge between South America and North America was absent, although South America was approaching the western subduction zone in the Pacific Ocean, causing both the rise of the Andes and a southward extension of the Meso-American peninsula. Mountain building took place in western North America and East Asia. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines.
Well studied continental exposures occur in Argentina. India continued creating dramatic new mountain ranges; the Tethys Seaway continued to shrink and disappeared as Africa collided with Eurasia in the Turkish–Arabian region between 19 and 12 Ma. The subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea near the end of the Miocene; the global trend was towards increasing aridity caused by global cooling reducing the ability of the atmosphere to absorb moisture. Uplift of East Africa in the late Miocene was responsible for the shrinking of tropical rain forests in that region, Australia got drier as it entered a zone of low rainfall in the Late Miocene. During the Oligocene and Early Miocene the coast of northern Brazil, south-central Peru, central Chile and large swathes of inland Patagonia were subject to a marine transgression; the transgressions in the west coast of South America is thought to be caused by a regional phenomenon while the rising central segment of the Andes represents an exception.
While there are numerous registers of Oligo-Miocene transgressions around the world it is doubtful that these correlate. It is thought that the Oligo-Miocene transgression in Patagonia could have temporarily linked the Pacific and Atlantic Oceans, as inferred from the findings of marine invertebrate fossils of both Atlantic and Pacific affinity in La Cascada Formation. Connection would have occurred through narrow epicontinental seaways that formed channels in a dissected topography; the Antarctic Plate started to subduct beneath South America 14 million years ago in the Miocene, forming the Chile Triple Junction. At first the Antarctic Plate subducted only in the southernmost tip of Patagonia, meaning that the Chile Triple Junction lay near the Strait of Magellan; as the southern part of Nazca Plate and the Chile Rise became consumed by subduction the more northerly regions of the Antarctic Plate begun to subduct beneath Patagonia so that the Chile Triple Junction advanced to the north over time.
The asthenospheric window associated to the triple junction disturbed previous patterns of mantle convection beneath Patagonia inducing an uplift of ca. 1 km that reversed the Oligocene–Miocene transgression. Climates remained moderately warm, although the slow global cooling that led to the Pleistocene glaciations continued. Although a long-term cooling trend was well underway, there is evidence of a warm period during the Miocene when the global climate rivalled that of the Oligocene; the Miocene warming b
Mitochondrial DNA
Mitochondrial DNA is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, adenosine triphosphate. Mitochondrial DNA is only a small portion of the DNA in a eukaryotic cell. In humans, the 16,569 base pairs of mitochondrial DNA encode for only 37 genes. Human mitochondrial DNA was the first significant part of the human genome to be sequenced. In most species, including humans, mtDNA is inherited from the mother. However, in exceptional cases, human babies sometimes inherit mtDNA from both their fathers and their mothers resulting in mtDNA heteroplasmy. Since animal mtDNA evolves faster than nuclear genetic markers, it represents a mainstay of phylogenetics and evolutionary biology, it permits an examination of the relatedness of populations, so has become important in anthropology and biogeography. Nuclear and mitochondrial DNA are thought to be of separate evolutionary origin, with the mtDNA being derived from the circular genomes of the bacteria that were engulfed by the early ancestors of today's eukaryotic cells.
This theory is called the endosymbiotic theory. Each mitochondrion is estimated to contain 2–10 mtDNA copies. In the cells of extant organisms, the vast majority of the proteins present in the mitochondria are coded for by nuclear DNA, but the genes for some, if not most, of them are thought to have been of bacterial origin, having since been transferred to the eukaryotic nucleus during evolution; the reasons why mitochondria have retained some genes are debated. The existence in some species of mitochondrion-derived organelles lacking a genome suggests that complete gene loss is possible, transferring mitochondrial genes to the nucleus has several advantages; the difficulty of targeting remotely-produced hydrophobic protein products to the mitochondrion is one hypothesis for why some genes are retained in mtDNA. Recent analysis of a wide range of mtDNA genomes suggests that both these features may dictate mitochondrial gene retention. In most multicellular organisms, mtDNA is inherited from the mother.
Mechanisms for this include simple dilution, degradation of sperm mtDNA in the male genital tract and in the fertilized egg. Whatever the mechanism, this single parent pattern of mtDNA inheritance is found in most animals, most plants and in fungi. In sexual reproduction, mitochondria are inherited from the mother. Most mitochondria are present at the base of the sperm's tail, used for propelling the sperm cells. In 1999 it was reported that paternal sperm mitochondria are marked with ubiquitin to select them for destruction inside the embryo; some in vitro fertilization techniques injecting a sperm into an oocyte, may interfere with this. The fact that mitochondrial DNA is maternally inherited enables genealogical researchers to trace maternal lineage far back in time; this is accomplished on human mitochondrial DNA by sequencing the hypervariable control regions, sometimes the complete molecule of the mitochondrial DNA, as a genealogical DNA test. HVR1, for example, consists of about 440 base pairs.
These 440 base pairs are compared to the same regions of other individuals to determine maternal lineage. Most the comparison is made with the revised Cambridge Reference Sequence. Vilà et al. have published studies tracing the matrilineal descent of domestic dogs from wolves. The concept of the Mitochondrial Eve is based on the same type of analysis, attempting to discover the origin of humanity by tracking the lineage back in time. MtDNA is conserved, its slow mutation rates make it useful for studying the evolutionary relationships—phylogeny—of organisms. Biologists can determine and compare mtDNA sequences among different species and use the comparisons to build an evolutionary tree for the species examined. However, due to the slow mutation rates, it is hard to distinguish between related species to any large degree, so other methods of analysis must be used. Entities subject to uniparental inheritance and with little to no recombination may be expected to be subject to Muller's ratchet, the accumulation of deleterious mutations until functionality is lost.
Animal populations of mitochondria avoid this through a developmental process known as the mtDNA bottleneck. The bottleneck exploits random processes in the cell to increase the cell-to-cell variability in mutant load as an organism develops: a single egg cell with some proportion of mutant mtDNA thus produces an embryo in which different cells have different mutant loads. Cell-level selection may act to remove those cells with more mutant mtDNA, leading to a stabilisation or reduction in mutant load between generations; the mechanism underlying the bottleneck is debated, with a recent mathematical and experimental
Ordovician
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago to the start of the Silurian Period 443.8 Mya. The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, placed them in a system of their own; the Ordovician received international approval in 1960, when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambrian period, although the end of the period was marked by the Ordovician–Silurian extinction events.
Invertebrates, namely molluscs and arthropods, dominated the oceans. The Great Ordovician Biodiversification Event increased the diversity of life. Fish, the world's first true vertebrates, continued to evolve, those with jaws may have first appeared late in the period. Life had yet to diversify on land. About 100 times as many meteorites struck the Earth per year during the Ordovician compared with today; the Ordovician Period began with a major extinction called the Cambrian–Ordovician extinction event, about 485.4 Mya. It lasted for about 42 million years and ended with the Ordovician–Silurian extinction events, about 443.8 Mya which wiped out 60% of marine genera. The dates given are recent radiometric dates and vary from those found in other sources; this second period of the Paleozoic era created abundant fossils that became major petroleum and gas reservoirs. The boundary chosen for the beginning of both the Ordovician Period and the Tremadocian stage is significant, it correlates well with the occurrence of widespread graptolite and trilobite species.
The base of the Tremadocian allows scientists to relate these species not only to each other, but to species that occur with them in other areas. This makes it easier to place many more species in time relative to the beginning of the Ordovician Period. A number of regional terms have been used to subdivide the Ordovician Period. In 2008, the ICS erected a formal international system of subdivisions. There exist Baltoscandic, Siberian, North American, Chinese Mediterranean and North-Gondwanan regional stratigraphic schemes; the Ordovician Period in Britain was traditionally broken into Early and Late epochs. The corresponding rocks of the Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column; the faunal stages from youngest to oldest are: Late Ordovician Hirnantian/Gamach Rawtheyan/Richmond Cautleyan/Richmond Pusgillian/Maysville/Richmond Middle Ordovician Trenton Onnian/Maysville/Eden Actonian/Eden Marshbrookian/Sherman Longvillian/Sherman Soudleyan/Kirkfield Harnagian/Rockland Costonian/Black River Chazy Llandeilo Whiterock Llanvirn Early Ordovician Cassinian Arenig/Jefferson/Castleman Tremadoc/Deming/Gaconadian The Tremadoc corresponds to the Tremadocian.
The Floian corresponds to the lower Arenig. The Llanvirn occupies the rest of the Darriwilian, terminates with it at the base of the Late Ordovician; the Sandbian represents the first half of the Caradoc. During the Ordovician, the southern continents were collected into Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician, the continents of Laurentia and Baltica were still independent continents, but Baltica began to move towards Laurentia in the period, causing the Iapetus Ocean between them to shrink; the small continent Avalonia separated from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia. The Taconic orogeny, a major mountain-building episode, was well under way in Cambrian times. In the early and middle Ordovician, temperatures were mild, but at the beginning of the Late Ordovician, from 460 to 450 Ma, volcanoes along the margin of the Iapetus Ocean spewed massive amounts of carbon dioxide, a greenhouse gas, into the atmosphere, turning the planet into a hothouse.
Sea levels were high, but as Gondwana moved south, ice accumulated into glaciers and sea levels dropped. At first, low-lying sea beds increased diversity, but glaciation led to mass extinctions as the seas drained and continental shelves became dry land. During the Ordovician, in fact during the Tremadocian, marine transgressions worldwide were the greatest for which evidence is preserved; these volcanic island arcs collided with proto North America to form the Appalachian mountains. By the end of the Late Ordovician the volcanic emissions had stopped. Gondwana had by that time neared the South Pole and was glaciated
