Ordovician period 488. 3 - 443. 7 million years ago ↓ PЄ Є O S D C P T J K PG N
Mean atmospheric O2 content over period duration	ca. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 The Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of The Paleogene (alternatively Palaeogene) is a geologic period and system that began 65 The Neogene is a geologic period and system starting 2303 ± 0 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 13. 5 Vol %[1] (68 % of modern level)
Mean atmospheric CO2 content over period duration	ca. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single 4200 ppm[2] (15 times pre-industrial level)
Mean surface temperature over period duration	ca. "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly 16°C [3] (2°C above modern level)
Key events in the Ordovician view • discuss • edit -490 — – -485 — – -480 — – -475 — – -470 — – -465 — – -460 — – -455 — – -450 — – -445 — –     Cambrian   Tremadocian Floian Dapingian Darriwilian Sandbian Katian Hirnantian Hirnantian Early Ordovician Llanvirn Llandeilo Caradoc Ashgill Silurian     ← First land plant spores[4] O r d o v i c i a n  Palæozoic Key events of the Ordovician period. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Tremadocian is the first internationally-recognized stage of the Ordovician Period of the Paleozoic Era. In Geology, the Arenig group is the name applied to the lowest stage of the Ordovician System The Darriwilian Faunal stage includes most of the Late Llanwirn The Hirnantian is the seventh and final internationally-recognized stage of the Ordovician Period of the Paleozoic Era. The Hirnantian is the seventh and final internationally-recognized stage of the Ordovician Period of the Paleozoic Era. The Early Ordovician, also called the Lower Ordovician by Geologists is the first subdivision of the Ordovician period and marked a great diversification The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 Llandeilo (or Llandilo is a Town in Carmarthenshire, south-west Wales, situated at the crossing of the River Tywi by the A483 Caradoc Vreichvras (more correctly in Welsh, Caradog Freichfras, meaning Caradoc Strong (or Stout Arm) was a semi-legendary ancestor to the kings Ashgill is a village in South Lanarkshire, Scotland. The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The embryophytes are the most familiar group of Plants They include Trees Flowers Ferns Mosses and various other green In Biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" Left: ICS approved stages. Right: "General" stages. Axis scale: millions of years ago.

The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488. The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" 3±1. 7 to 443. 7±1. 5 million years ago (ICS, 2004)^[5]. The International Commission on Stratigraphy (ICS, sometimes referred to by the unofficial " International Stratigraphic Commission " is a daughter or major Subcommittee It follows the Cambrian period and is followed by the Silurian period. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The Ordovician, named after the Welsh 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 periods respectively. The Ordovices were one of the Celtic tribes living in the British Islands before the Roman invasion of Britain. Charles Lapworth ( September 20, 1842 &ndash March 13, 1920) was an English geologist. Adam Sedgwick ( 22 March 1785 &ndash 27 January 1873) was one of the founders of modern Geology. Sir Roderick Impey Murchison 1st Baronet KCB FRS ( 19 February, 1792 &ndash 22 October, 1871) was an influential In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 Lapworth, recognizing that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, realized that they should be placed in a period of their own. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Fauna is all of the Animal life of any particular region or time In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes

While recognition of the distinct Ordovician period was slow in the United Kingdom, other areas of the world accepted it quickly. The United Kingdom of Great Britain and Ireland was the formal name of the United Kingdom from 1 January 1801 until 12 April 1927 It received international sanction in 1906, when it was adopted as an official period of the Paleozoic era by the International Geological Congress. Year 1906 ( MCMVI) was a Common year starting on Monday (link will display full calendar of the Gregorian calendar (or a Common year starting

Ordovician dating

The Ordovician period started at a major extinction event called the Cambrian-Ordovician extinction events some time about 488. The Cambrian–Ordovician extinction event occurred approximately 488 million years ago 3 ± 1. 7 million years ago (Mya) and lasted for about 44. In Astronomy, Geology, and Paleontology, mya or " mya " is an abbreviation for "million years ago". 6 million years. It ended with another major extinction event about 443. 7 ± 1. 5 Ma (ICS, 2004) that wiped out 60% of marine genera. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic A. Melott et al. (ref. 2006) suggested a ten-second gamma ray burst could have destroyed the ozone layer and exposed terrestrial and marine surface-dwelling life to deadly radiation, but most scientists agree that extinction events are complex with multiple causes. Gamma-ray bursts ( GRB s are the most luminous electromagnetic events occurring in the Universe since the Big Bang. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy See below. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488

The dates given are recent radiometric dates and vary slightly from those used in other sources. In Optics, radiometry is the field that studies the Measurement of Electromagnetic radiation, including Visible light. This second period of the Paleozoic era created abundant fossils and in some regions, major petroleum and gas reservoirs. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Petroleum ( L petroleum, from Greek πετρέλαιον, lit This page is about the physical properties of gas as a state of matter

Ordovician subdivisions

The Ordovician Period is usually broken into Early (Tremadoc and Arenig), Middle (Llanvirn [subdivided into Abereiddian and Llandeilian]) and Late (Caradoc and Ashgill) epochs. In Geology, the Arenig group is the name applied to the lowest stage of the Ordovician System In geology Caradoc Series is the name introduced by Roderick Murchison in 1839 for the sandstone series of Caer Caradoc in Shropshire, England 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 (subdivisions of epochs) from youngest to oldest are:

• Hirnantian/Gamach (Late Ordovician: Ashgill)
• Rawtheyan/Richmond (Late Ordovician: Ashgill)
• Cautleyan/Richmond (Late Ordovician: Ashgill)
• Pusgillian/Maysville/Richmond (Late Ordovician: Ashgill)

• Trenton (Middle Ordovician: Caradoc)
• Onnian/Maysville/Eden (Middle Ordovician: Caradoc)
• Actonian/Eden (Middle Ordovician: Caradoc)
• Marshbrookian/Sherman (Middle Ordovician: Caradoc)
• Longvillian/Sherman (Middle Ordovician: Caradoc)
• Soundleyan/Kirkfield (Middle Ordovician: Caradoc)
• Harnagian/Rockland (Middle Ordovician: Caradoc)
• Costonian/Black River (Middle Ordovician: Caradoc)
• Chazy (Middle Ordovician: Llandeilo)
• Llandeilo (Middle Ordovician: Llandeilo)
• Whiterock (Middle Ordovician: Llanvirn)
• Llanvirn (Middle Ordovician: Llanvirn)

• Cassinian (Early Ordovician: Arenig)
• Arenig/Jefferson/Castleman (Early Ordovician: Arenig)
• Tremadoc/Deming/Gaconadian (Early Ordovician: Tremadoc)

Ordovician paleogeography

Sea levels were high during the Ordovician; in fact during the Tremadocian, marine transgressions worldwide were the greatest for which evidence is preserved in the rocks. The Hirnantian is the seventh and final internationally-recognized stage of the Ordovician Period of the Paleozoic Era. A transgression is a geologic event during which Sea level rises relative to the land and the shoreline moves toward higher ground resulting in flooding

During the Ordovician, the southern continents were collected into a single continent called Gondwana. Gondwana (ɡɒnˈdwɑːnə originally Gondwanaland) was a southern Supercontinent that existed about 500 to 200 Ma ago Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. Early in the Ordovician, the continents Laurentia, Siberia, and Baltica were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move towards Laurentia later in the period, causing the Iapetus Ocean to shrink between them. Laurentia (also known as the North American craton) like all Craton land was created as continents moved about the surface of the Earth Siberia is the Craton located in the heart of the region of Siberia. Baltica redirects here For the Russian beer, see Baltika Breweries Baltica is a name applied by geologists to a late- Proterozoic, In Geology, a supercontinent is a Landmass comprising more than one Continental core or Craton. Pannotia, first described by Ian W D Dalziel in 1997 is a hypothetical Supercontinent that existed from the Pan-African orogeny about 600 million years ago to the The Iapetus Ocean was an Ocean that existed in the Southern Hemisphere between Laurentia ( Scotland and North America) and Baltica Also, Avalonia broke free from Gondwana and began to head north towards Laurentia. Avalonia was an ancient Microcontinent or Terrane whose history formed much of the older rocks of Western Europe, Atlantic Canada and parts of the Rheic Ocean was formed as a result of this. The Rheic Ocean was an Ocean in the Paleozoic Era that existed between to the north the Continent of Baltica (northern

Ordovician rocks are chiefly sedimentary. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Because of the restricted area and low elevation of solid land, which set limits to erosion, marine sediments that make up a large part of the Ordovician system consist chiefly of limestone. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Shale and sandstone are less conspicuous. Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains.

A major mountain-building episode was the Taconic orogeny that was well under way in Cambrian times. The Taconic orogeny was a great mountain building period that perhaps had the greatest overall effect on the geologic structure of basement rocks within the New York Bight

By the end of the period, Gondwana had neared or approached the pole and was largely glaciated. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period.

The Ordovician was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate. A calcite sea is one in which low-magnesium Calcite is the primary inorganic marine Calcium carbonate precipitate Carbonate hardgrounds were thus very common, along with calcitic ooids, calcitic cements, and invertebrate faunas with dominantly calcitic skeletons (Stanley and Hardie, 1998, 1999). Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer 1992 Ooids are small ( Sedimentary grains usually composed of Calcium carbonate, but sometimes made up of Iron

Climate

The Early Ordovician climate was thought to be quite warm, at least in the tropics. As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts. Panthalassic Ocean covered much of the northern hemisphere, and other minor oceans included Proto-Tethys, Paleo-Tethys, Khanty Ocean which was closed off by the Late Ordovician, Iapetus Ocean, and the new Rheic Ocean. Panthalassa ( Greek, meaning 'all seas' also known as the Panthalassic Ocean, was the vast global Ocean that surrounded the Supercontinent The Proto-Tethys Ocean was an ancient Ocean that existed from the latest Ediacaran to the Carboniferous (550-330 Ma) The Paleo-Tethys Ocean was an ancient Paleozoic Ocean. It was located between the Paleocontinent Gondwana and the so called Hunic terranes Khanty Ocean was an ancient small ocean that existed near the end of the Precambrian time to the Silurian. The Iapetus Ocean was an Ocean that existed in the Southern Hemisphere between Laurentia ( Scotland and North America) and Baltica The Rheic Ocean was an Ocean in the Paleozoic Era that existed between to the north the Continent of Baltica (northern

As the Ordovician progressed, we see evidence of glaciers on the land we now know as Africa and South America. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a At the time these land masses were sitting at the South Pole, and covered by ice caps. The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. An ice cap is an Ice mass that covers less than 50 000 km² of land area (usually covering a highland area

Ordovician Life

Ordovician fauna

Artist impression of the Ordovician Sea.

Though less famous than the Cambrian explosion, the Ordovician featured an adaptive radiation that was no less remarkable; marine faunal genera increased fourfold, resulting in 12% of all known Phanerozoic marine fauna. The Cambrian explosion or Cambrian radiation was the seemingly rapid appearance of most major groups of complex Animals around, as evidenced by the An adaptive radiation is a rapid Evolutionary radiation characterized by an increase in the morphological and ecological diversity of a single rapidly diversifying lineage A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed ^[6] The trilobite, inarticulate brachiopod, archaeocyathid, and eocrinoid faunas of the Cambrian were succeeded by those which would dominate for the rest of the Paleozoic, such as articulate brachiopods, cephalopods, and crinoids; articulate brachiopods, in particular, largely replaced trilobites in shelf communities. Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also The Archaeocyatha or archaeocyathids ("ancient cups" were Sessile The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the Echinoderms (phylum Echinodermata The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such ^[7] Their success epitomizes the greatly increased diversity of carbonate shell-secreting organisms in the Ordovician compared to the Cambrian. Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 ^[8]

In North America and Europe, the Ordovician was a time of shallow continental seas rich in life. Trilobites and brachiopods in particular were rich and diverse. The first bryozoa appeared in the Ordovician as did the first coral reefs. Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some Coral reefs are Aragonite structures produced by living organisms found in marine waters with little to no nutrients in the water Solitary corals date back to at least the Cambrian. Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with Molluscs, which had also appeared during the Cambrian or the Ediacaran, became common and varied, especially bivalves, gastropods, and nautiloid cephalopods. Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Bivalves are Molluscs belonging to the class Bivalvia. They have two-part shells and typically both valves are symmetrical along the hinge line The class Gastropoda or the gastropods, also previously known as gasteropods, or univalves, and more commonly known as Snails Nautiloids are a group of marine Mollusks in the subclass Nautiloidea, which all possess an external shell the best-known example being the modern Nautiluses It was long thought that the first true vertebrates (fish - Ostracoderms) appeared in the Ordovician, but recent discoveries in China reveal that they probably originated in the Early Cambrian. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Ostracoderms ("shell-skinned" are any of several groups of extinct, primitive jawless Fishes that were covered in an armor of bony plates China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The very first jawed fish appeared in the Late Ordovician epoch. Gnathostomata is the group of Vertebrates with Jaws The group is traditionally a superclass, including the familiar classes of Fish, The Late Ordovician, also called the Upper Ordovician by Geologists is the third epoch of the Ordovician period Now-extinct marine animals called graptolites thrived in the oceans. Graptolites (Graptolithina are Fossil colonial Animals known chiefly from the Upper Cambrian through the Lower Carboniferous ( Mississippian Some cystoids and crinoids appeared.

During the Middle Ordovician there was a large increase in the intensity and diversity of bioeroding organisms. This is known as the Ordovician Bioerosion Revolution (Wilson & Palmer, 2006). Bioerosion describes the Erosion of hard ocean substrates by living organisms by a number of mechanisms It is marked by a sudden abundance of hard substrate trace fossils such as Trypanites, Palaeosabella and Petroxestes.

Trilobites in the Ordovician were very different than their predecessors in the Cambrian, Many trilobites developed bizarre spines and nodules to defend against predators such as primitive sharks and Nautiloid cephalopods while other trilobites such as Aeglina prisca evolved to become swimming forms. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with Sharks ( Superorder Selachimorpha) are a type of Fish with a full cartilaginous Skeleton and a highly streamlined body Some trilobites even developed shovel-like snouts for ploughing through muddy sea bottoms. Another unusual clade of trilobites known as the Trinucleids developed a broad pitted margin around their head shields. ^[9]

Other trilobites such as (Asaphus kowalewski) evolved long eyestalks to assist in detecting predators while some trilobite eyes by contrast took the opposing evolutionary direction and disappeared completely. Asaphus kowalewskii is one of the 35 species of Trilobite of the Genus Asaphus (this particular species is sometimes placed in its own ^[10]

The Upper Ordovician edrioasteroid Cystaster stellatus on a cobble from the Kope Formation in northern Kentucky. The edrioasteroid is about 1. 5 cm in diameter. In the background is the cyclostome bryozoan Corynotrypa. Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some	Fossil Mountain, west-central Utah; Middle Ordovician fossiliferous shales and limestones in the lower half.	Outcrop of Upper Ordovician rubbly limestone and shale, southern Indiana; College of Wooster students.	Outcrop of Upper Ordovician limestone and minor shale, central Tennessee; College of Wooster students.
Trypanites borings in an Ordovician hardground, southeastern Indiana; see Wilson and Palmer (2001). Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer 1992	Petroxestes borings in an Ordovician hardground, southern Ohio; see Wilson and Palmer (2006). Carbonate hardgrounds are surfaces of synsedimentarily cemented carbonate layers that have been exposed on the seafloor (Wilson and Palmer 1992	Outcrop of Ordovician kukersite oil shale, northern Estonia. Kukersite is a marine type Oil shale of Ordovician age found in the Baltic Oil Shale Basin in Estonia and North-West Russia Estonia, officially the Republic of Estonia ( Eesti or Eesti Vabariik) is a Country in Northern Europe in the Baltic region	Fossils in Ordovician kukersite oil shale, northern Estonia. Estonia, officially the Republic of Estonia ( Eesti or Eesti Vabariik) is a Country in Northern Europe in the Baltic region
Brachiopods and bryozoans in an Ordovician limestone, southern Minnesota. Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some	Ordovician bryozoa, Batavia, Ohio. Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some	The Ordovician cystoid Echinosphaerites (an extinct echinoderm) from northeastern Estonia; approximately 5 cm in diameter. Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars)	Prasopora, a trepostome bryozoan from the Ordovician of Iowa. Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some
An Ordovician strophomenid brachiopod with encrusting inarticulate brachiopods and a bryozoan.

Ordovician flora

Green algae were common in the Ordovician and Late Cambrian (perhaps earlier). The green algae (singular green alga) are the large group of Algae from which the Embryophytes (higher plants emerged The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with Plants probably evolved from green algae. The first terrestrial plants appeared in the form of tiny non-vascular plants resembling liverworts. Plants are living Organisms belonging to the kingdom Plantae. The Marchantiophyta are a division of Bryophyte Plants commonly referred to as hepatics or liverworts. Fossil spores from land plants have been identified in uppermost Ordovician sediments, but among the first land fungi may have been Arbuscular mycorrhiza fungi (Glomerales), playing a crucial role in facilitating the colonization of land by plants through mycorrhizal symbiosis, which makes mineral nutrients available to plant cells; such fossilized fungal hyphae and spores from the Ordovician of Wisconsin have been found with an age of about 460 million years ago, a time when the land flora most likely only consisted of plants similar to non-vascular bryophytes. A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ An arbuscular mycorrhiza (plural mycorrhizae or mycorrhizas) is a type of Mycorrhiza in which the Fungus penetrates the cortical cells of the Glomerales is an order of Symbiotic Fungi within the phylum Glomeromycota. Bryophytes are all Embryophytes ('land Plants) that are non-vascular: they have tissues and enclosed reproductive systems but they lack Vascular tissue ^[11]

Marine fungi were abundant in the Ordovician seas to decompose animal carcasses, and other wastes. Decomposition (or spoilage) refers to the break down of tissue of a formerly living Organism into simpler forms of matter

End of the Ordovician

Main article: Ordovician-Silurian extinction events

The Ordovician came to a close in a series of extinction events that, taken together, comprise the second largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct. An extinction event (also known as mass extinction; extinction-level event, ELE is a sharp decrease in the number of Species in a relatively short period The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic The only larger one was the Permian-Triassic extinction event.

The extinctions occurred approximately 444-447 million years ago and mark the boundary between the Ordovician and the following Silurian Period. The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 At that time all complex multicellular organisms lived in the sea, and about 49% of genera of fauna disappeared forever; brachiopods and bryozoans were decimated, along with many of the trilobite, conodont and graptolite families. Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita. Conodonts are extinct chordates resembling eels classified in the class Conodonta. Graptolites (Graptolithina are Fossil colonial Animals known chiefly from the Upper Cambrian through the Lower Carboniferous ( Mississippian

The most commonly accepted theory is that these events were triggered by the onset of an ice age, in the Hirnantian faunal stage that ended the long, stable greenhouse conditions typical of the Ordovician. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets A greenhouse (also called a glasshouse or hothouse) is a building where plants are cultivated The ice age was probably not as long-lasting as once thought; study of oxygen isotopes in fossil brachiopods shows that it was probably no longer than 0. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides 5 to 1. 5 million years. ^[12] The event was preceded by a fall in atmospheric carbon dioxide (from 7000ppm to 4400ppm) which selectively affected the shallow seas where most organisms lived. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it, which have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time. Gondwana (ɡɒnˈdwɑːnə originally Gondwanaland) was a southern Supercontinent that existed about 500 to 200 Ma ago North Africa or Northern Africa is the Northernmost Region of the African Continent, separated by the Sahara from Sub-Saharan

Glaciation locks up water from the world-ocean, and the interglacials free it, causing sea levels repeatedly to drop and rise; the vast shallow intra-continental Ordovician seas withdrew, which eliminated many ecological niches, then returned carrying diminished founder populations lacking many whole families of organisms, then withdrew again with the next pulse of glaciation, eliminating biological diversity at each change. ^[13] Species limited to a single epicontinental sea on a given landmass were severely affected. ^[14] Tropical lifeforms were hit particularly hard in the first wave of extinction, while cool-water species were hit worst in the second pulse. ^[15]

Surviving species were those that coped with the changed conditions and filled the ecological niches left by the extinctions.

At the end of the second event, melting glaciers caused the sea level to rise and stabilise once more. The rebound of life's diversity with the permanent re-flooding of continental shelves at the onset of the Silurian saw increased biodiversity within the surviving Orders.

Notes

1. ^ http://de.wikipedia.org/wiki/Bild:Sauerstoffgehalt-1000mj.svg
2. ^ http://en.wikipedia.org/wiki/Image:Phanerozoic_Carbon_Dioxide.png
3. ^ http://en.wikipedia.org/wiki/Image:All_palaeotemps.png
4. ^ Wellman, C. H. , Gray, J. (2000). "The microfossil record of early land plants". Philosophical Transactions: Biological Sciences 355 (1398): 717-732.  
5. ^ Gradstein, F. M. ; Ogg, J. G. ; Smith, A. G. (2004). A Geologic Time Scale 2004. Cambridge university press.  
6. ^ Dougal Dixon et al. , Atlas of Life on Earth, (New York: Barnes & Noble Books, 2001), p. 87.
7. ^ John D. Cooper, Richard H. Miller, and Jacqueline Patterson, A Trip Through Time: Principles of Historical Geology, (Columbus: Merrill Publishing Company, 1986), pp. 247, 255-9.
8. ^ Ibid. , 255-6.
9. ^ Palaeos Paleozoic : Ordovician : The Ordovician Period
10. ^ A Guide to the Orders of Trilobites
11. ^ Redecker, D. ; Kodner, R.  ; Graham, L. E. (2000). "Glomalean fungi from the Ordovician". Science 289 (5486): 1920-1921. Science is the Academic journal of the American Association for the Advancement of Science and is considered one of the world's most prestigious Scientific doi:10.1126/science.289.5486.1920. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
12. ^ Steven M. Stanley, Earth System History, (New York: W. H. Freeman and Company, 1999), 358.
13. ^ Emiliani, (1992), 491
14. ^ Stanley, 360.
15. ^ Stanley, 360

References

• Ogg, Jim, June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
• Stanley, Steven M. , Earth System History. New York: W. H. Freeman and Company, 1999. ISBN 0-7167-2882-6
• Stanley, S. M. and Hardie, L. A. (1998). "Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry". Palaeogeography, Palaeoclimatology, Palaeoecology 144: 3-19.
• Stanley, S. M. and Hardie, L. A. (1999). "Hypercalcification; paleontology links plate tectonics and geochemistry to sedimentology". GSA Today 9: 1-7.
• Mehrtens, Dr. Charlotte, "Chazy Reef at Isle La Motte". An Ordovician reef in Vermont.
• Adrian Melott et al., "Did a gamma-ray burst initiate the late Ordovician mass extinction?" International Journal of Astrobiology 3 (2004) 55
• BBC News, " Ray burst is extinction suspect", 11 April 2005.
• ABC News, "Ray burst may have wiped out life on Earth", 29 April 2004
• Wilson, M. A. and Palmer, T. J. , 2001. Domiciles, not predatory borings: a simpler explanation of the holes in Ordovician shells analyzed by Kaplan and Baumiller, 2000. Palaios 16:524-525.
• Wilson, M. A. and Palmer, T. J. 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109-112. [1]

External links

• Examples of Ordovician Fossils
• Ordovician fossils of the famous Cincinnatian Group
• The Dry Dredgers, an active group of amateur paleontologists in the Cincinnati area