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The Silurian
Silurian
is a geologic period and system spanning 24.6 million years from the end of the Ordovician
Ordovician
Period, at 443.8 million years ago (Mya), to the beginning of the Devonian
Devonian
Period, 419.2 Mya.[8] As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian
Silurian
is set at a series of major Ordovician–Silurian extinction events
Ordovician–Silurian extinction events
when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian
Silurian
was the diversification of jawed and bony fish. Multi-cellular life also began to appear on land in the form of small, bryophyte-like and vascular plants that grew beside lakes, streams, and coastlines, and terrestrial arthropods are also first found on land during the Silurian. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian.

Contents

1 History of study 2 Subdivisions

2.1 Llandovery 2.2 Wenlock 2.3 Ludlow 2.4 Přídolí 2.5 Regional stages

3 Geography 4 Climate and sea level

4.1 Perturbations

5 Flora and fauna 6 Notes 7 References 8 External links

History of study[edit]

Life
Life
timeline

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-4500 — – -4000 — – -3500 — – -3000 — – -2500 — – -2000 — – -1500 — – -1000 — – -500 — – 0 —

water

Single-celled life

photosynthesis

Eukaryotes

Multicellular life

Land life

Dinosaurs    

Mammals

Flowers

 

Earliest Earth
Earth
(−4540)

Earliest water

Earliest life

LHB meteorites

Earliest oxygen

Atmospheric oxygen

Oxygen
Oxygen
crisis

Earliest sexual reproduction

Ediacara biota

Cambrian
Cambrian
explosion

Earliest humans

P h a n e r o z o i c

P r o t e r o z o i c

A r c h e a n

H a d e a n

Pongola

Huronian

Cryogenian

Andean

Karoo

Quaternary

Axis scale: million years Orange labels: ice ages. Also see: Human
Human
timeline and Nature timeline

The Silurian
Silurian
system was first identified by British geologist Roderick Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales
Wales
in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, from the Latin
Latin
name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian
Silurian
rocks and the land inhabited by the Silures (cf. Geologic map of Wales, Map of pre-Roman tribes of Wales). In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian
Cambrian
Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, which was the germ of the modern geological time scale. As it was first identified, the "Silurian" series when traced farther afield quickly came to overlap Sedgwick's "Cambrian" sequence, however, provoking furious disagreements that ended the friendship. Charles Lapworth resolved the conflict by defining a new Ordovician
Ordovician
system including the contested beds. An early alternative name for the Silurian
Silurian
was "Gotlandian" after the strata of the Baltic island of Gotland. The French geologist Joachim Barrande, building on Murchison's work, used the term Silurian
Silurian
in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian
Silurian
rocks of Bohemia
Bohemia
into eight stages. His interpretation was questioned in 1854 by Edward Forbes, and the later stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia
Bohemia
as a classic ground for the study of the earliest fossils. Subdivisions[edit] Llandovery[edit] See also: Llandovery
Llandovery
Group The Llandovery
Llandovery
Epoch lasted from 443.8 ± 1.5 to 433.4 ± 2.8 mya, and is subdivided into three stages: the Rhuddanian,[9] lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years ago, and the Telychian. The epoch is named for the town of Llandovery
Llandovery
in Carmarthenshire, Wales. Wenlock[edit] See also: Wenlock (Silurian) The Wenlock, which lasted from 433.4 ± 1.5 to 427.4 ± 2.8 mya, is subdivided into the Sheinwoodian (to 430.5 million years ago) and Homerian ages. It is named after Wenlock Edge
Wenlock Edge
in Shropshire, England. During the Wenlock, the oldest-known tracheophytes of the genus Cooksonia, appear. The complexity of slightly later Gondwana
Gondwana
plants like Baragwanathia, which resembled a modern clubmoss, indicates a much longer history for vascular plants, extending into the early Silurian
Silurian
or even Ordovician.[citation needed] The first terrestrial animals also appear in the Wenlock, represented by air-breathing millipedes from Scotland.[10] Ludlow[edit] See also: Ludlow
Ludlow
Group The Ludlow, lasting from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, and the Ludfordian stage. It is named for the town of Ludlow
Ludlow
(and neighbouring Ludford) in Shropshire, England. Přídolí [edit] The Přídolí, lasting from 423 ± 1.5 to 419.2 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague
Prague
suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area.[11] Regional stages[edit] In North America a different suite of regional stages is sometimes used:

Cayugan (Late Silurian
Silurian
– Ludlow) Lockportian (Middle Silurian: late Wenlock) Tonawandan (Middle Silurian: early Wenlock) Ontarian (Early Silurian: late Llandovery) Alexandrian (Earliest Silurian: early Llandovery)

In Estonia
Estonia
the following suite of regional stages is used:[12]

Ohessaare stage (Late Silurian
Silurian
– early Přídolí) Kaugatuma stage (Late Silurian
Silurian
– late Přídolí) Kuressaare stage (Late Silurian
Silurian
– late Ludlow) Paadla stage (Late Silurian
Silurian
– early Ludlow) Rootsiküla stage (Middle Silurian: late Wenlock) Jaagarahu stage (Middle Silurian: middle Wenlock) Jaani stage (Middle Silurian: early Wenlock) Adavere stage (Early Silurian: late Llandovery) Raikküla stage (Early Silurian: middle Llandovery) Juuru stage (Earliest Silurian: early Llandovery)

Geography[edit]

Ordovician- Silurian
Silurian
boundary on Hovedøya, Norway, showing gray Ordovician
Ordovician
sandstone and brown Silurian
Silurian
mudstone. The layers have been overturned by the Caledonian orogeny.

With the supercontinent Gondwana
Gondwana
covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe.[13] The high sea levels of the Silurian
Silurian
and the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and thus a rich diversity of environmental settings.[13] During the Silurian, Gondwana
Gondwana
continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian
Silurian
icecaps were less extensive than those of the late- Ordovician
Ordovician
glaciation. The southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian
Silurian
sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia
Laurentia
drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. When the proto-Europe collided with North America, the collision folded coastal sediments that had been accumulating since the Cambrian off the east coast of North America and the west coast of Europe. This event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway. At the end of the Silurian, sea levels dropped again, leaving telltale basins of evaporites extending from Michigan to West Virginia, and the new mountain ranges were rapidly eroded. The Teays River, flowing into the shallow mid-continental sea, eroded Ordovician Period strata, forming deposits of Silurian
Silurian
strata in northern Ohio and Indiana. The vast ocean of Panthalassa
Panthalassa
covered most of the northern hemisphere. Other minor oceans, include two phases of the Tethys, the Proto-Tethys and Paleo-Tethys, the Rheic Ocean, the Iapetus Ocean
Iapetus Ocean
(a narrow seaway between Avalonia
Avalonia
and Laurentia), and the newly formed Ural Ocean. Climate and sea level[edit] The Silurian
Silurian
period enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the Ordovician
Ordovician
before it, and the extreme heat of the ensuing Devonian.[13] Sea levels rose from their Hirnantian
Hirnantian
low throughout the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller scale patterns are superimposed on this general trend; fifteen high-stands can be identified, and the highest Silurian
Silurian
sea level was probably around 140 m higher than the lowest level reached.[13] During this period, the Earth
Earth
entered a long, warm greenhouse phase, supported by high CO2 levels of 4500 ppm, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole
South Pole
until they almost disappeared in the middle of Silurian. The period witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations. Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces. Later in the Silurian, the climate cooled slightly, but closer to the Silurian- Devonian
Devonian
boundary, the climate became warmer.[citation needed] Perturbations[edit] The climate and carbon cycle appears to be rather unsettled during the Silurian, which has a higher concentration of isotopic excursions than any other period.[13] The Ireviken event, Mulde event and Lau event each represent isotopic excursions following a minor mass extinction[14] and associated with rapid sea-level change, in addition to the larger extinction at the end of the Silurian.[13] Each one leaves a similar signature in the geological record, both geochemically and biologically; pelagic (free-swimming) organisms were particularly hard hit, as were brachiopods, corals and trilobites, and extinctions rarely occur in a rapid series of fast bursts.[13] Flora and fauna[edit] The Silurian
Silurian
was the first period to see megafossils of extensive terrestrial biota, in the form of moss-like miniature forests along lakes and streams. However, the land fauna did not have a major impact on the Earth
Earth
until it diversified in the Devonian.[13] The first fossil records of vascular plants, that is, land plants with tissues that carry water and food, appeared in the second half of the Silurian
Silurian
period.[15] The earliest-known representatives of this group are Cooksonia. Most of the sediments containing Cooksonia
Cooksonia
are marine in nature. Preferred habitats were likely along rivers and streams. Baragwanathia
Baragwanathia
appears to be almost as old, dating to the early Ludlow (420 million years) and has branching stems and needle-like leaves of 10–20 cm. The plant shows a high degree of development in relation to the age of its fossil remains. Fossils of this plant have been recorded in Australia,[16] Canada[17] and China.[18] Eohostimella heathana is an early, probably terrestrial, "plant" known from compression fossils[19] of early Silurian
Silurian
(Llandovery) age.[20] The chemistry of its fossils is similar to that of fossilised vascular plants, rather than algae.[19] The first bony fish, the Osteichthyes, appeared, represented by the Acanthodians covered with bony scales; fish reached considerable diversity and developed movable jaws, adapted from the supports of the front two or three gill arches. A diverse fauna of eurypterids (sea scorpions)—some of them several meters in length—prowled the shallow Silurian
Silurian
seas of North America; many of their fossils have been found in New York state. Leeches also made their appearance during the Silurian
Silurian
Period. Brachiopods, bryozoa, molluscs, hederelloids, tentaculitoids, crinoids and trilobites were abundant and diverse.[citation needed] Endobiotic symbionts were common in the corals and stromatoporoids.[21][22] Reef abundance was patchy; sometimes fossils are frequent but at other points are virtually absent from the rock record.[13] The earliest-known animals fully adapted to terrestrial conditions appear during the Mid-Silurian, including the millipede Pneumodesmus.[10] Some evidence also suggests the presence of predatory trigonotarbid arachnoids and myriapods in Late Silurian facies.[23] Predatory invertebrates would indicate that simple food webs were in place that included non-predatory prey animals. Extrapolating back from Early Devonian
Devonian
biota, Andrew Jeram et al. in 1990[24] suggested a food web based on as-yet-undiscovered detritivores and grazers on micro-organisms.[25]

Cooksonia, the earliest vascular plant, middle Silurian

Silurian
Silurian
sea bed fossils collected from Wren's Nest Nature Reserve, Dudley UK

Crinoid
Crinoid
fragments in a Silurian
Silurian
(Pridoli) limestone (Saaremaa, Estonia)

Silurian
Silurian
sea bed fossils collected from Wren's Nest Nature Reserve, Dudley UK

Artist's impression of Silurian
Silurian
underwater fauna

Eurypterus, a common Upper Silurian
Silurian
eurypterid

Poraspis

Notes[edit]

^ Image:Sauerstoffgehalt-1000mj.svg ^ File:OxygenLevel-1000ma.svg ^ Image: Phanerozoic
Phanerozoic
Carbon Dioxide.png ^ Image:All palaeotemps.png ^ Haq, B. U.; Schutter, SR (2008). "A Chronology of Paleozoic Sea-Level Changes". Science. 322 (5898): 64–68. Bibcode:2008Sci...322...64H. doi:10.1126/science.1161648. PMID 18832639.  ^ Jeppsson, L.; Calner, M. (2007). "The Silurian
Silurian
Mulde Event and a scenario for secundo—secundo events". Earth
Earth
and Environmental Science Transactions of the Royal Society of Edinburgh. 93 (02): 135–154. doi:10.1017/S0263593300000377.  ^ Munnecke, A.; Samtleben, C.; Bickert, T. (2003). "The Ireviken Event in the lower Silurian
Silurian
of Gotland, Sweden-relation to similar Palaeozoic and Proterozoic
Proterozoic
events". Palaeogeography, Palaeoclimatology, Palaeoecology. 195 (1): 99–124. doi:10.1016/S0031-0182(03)00304-3.  ^ "International Chronostratigraphic Chart v.2015/01" (PDF). International Commission on Stratigraphy. January 2015.  ^ Named for the Cefn-Rhuddan Farm in the Llandovery
Llandovery
area. ^ a b Paul Selden & Helen Read (2008). "The oldest land animals: Silurian
Silurian
millipedes from Scotland" (PDF). Bulletin of the British Myriapod
Myriapod
& Isopod Group. 23: 36–37.  ^ Manda, Štěpán; Frýda, Jiří (2010). "Silurian- Devonian
Devonian
boundary events and their influence on cephalopod evolution: evolutionary significance of cephalopod egg size during mass extinctions". Bulletin of Geoscience. 85 (3): 513–40. doi:10.3140/bull.geosci.1174.  ^ http://stratigraafia.info/materjalid/eesti_strat/Silurian_2015.pdf ^ a b c d e f g h i Munnecke, Axel; Calner, Mikael; Harper, David A.T.; Servais, Thomas (2010). " Ordovician
Ordovician
and Silurian
Silurian
sea–water chemistry, sea level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology. 296 (3–4): 389–413. doi:10.1016/j.palaeo.2010.08.001.  ^ Samtleben, C.; Munnecke, A.; Bickert, T. (2000). "Development of facies and C/O-isotopes in transects through the Ludlow
Ludlow
of Gotland: Evidence for global and local influences on a shallow-marine environment". Facies. 43: 1. doi:10.1007/BF02536983.  ^ Rittner, Don (2009). Encyclopedia of Biology. Infobase Publishing. p. 338. ISBN 9781438109992.  ^ Lang, W.H.; Cookson, I.C. (1935). "On a flora, including vascular land plants, associated with Monograptus, in rocks of Silurian
Silurian
age, from Victoria, Australia". Philosophical Transactions of the Royal Society of London B. 224 (517): 421–449. doi:10.1098/rstb.1935.0004.  ^ Hueber, F.M. (1983). "A new species of Baragwanathia
Baragwanathia
from the Sextant Formation (Emsian) Northern Ontario, Canada". Botanical Journal of the Linnean Society. 86 (1–2): 57–79. doi:10.1111/j.1095-8339.1983.tb00717.x.  ^ Bora, Lily (2010). Principles of Paleobotany. Mittal Publications. pp. 36–37.  ^ a b Niklas, Karl J. (1976). "Chemical Examinations of Some Non-Vascular Paleozoic
Paleozoic
Plants". Brittonia. New York Botanical Garden Press. 28 (1): 113. doi:10.2307/2805564. JSTOR 2805564.  ^ Edwards, D. & Wellman, C. (2001), "Embryophytes on Land: The Ordovician
Ordovician
to Lochkovian (Lower Devonian) Record", in Gensel, P. & Edwards, D., Plants Invade the Land : Evolutionary and Environmental Perspectives, New York: Columbia University Press, pp. 3–28, ISBN 978-0-231-11161-4 , p. 4 ^ Vinn, O.; wilson, M.A.; Mõtus, M.-A. (2014). "Symbiotic endobiont biofacies in the Silurian
Silurian
of Baltica". Palaeogeography, Palaeoclimatology, Palaeoecology. 404: 24–29. doi:10.1016/j.palaeo.2014.03.041. Retrieved 2014-06-11.  ^ Vinn, O.; Mõtus, M.-A. (2008). "The earliest endosymbiotic mineralized tubeworms from the Silurian
Silurian
of Podolia, Ukraine". Journal of Paleontology. 82 (2): 409–414. doi:10.1666/07-056.1. Retrieved 2014-06-11.  ^ Garwood, Russell J.; Edgecombe, Gregory D. (September 2011). "Early Terrestrial Animals, Evolution, and Uncertainty". Evolution: Education and Outreach. New York: Springer Science+Business Media. 4 (3): 489–501. doi:10.1007/s12052-011-0357-y. ISSN 1936-6426. Retrieved 2015-07-21.  ^ Jeram, Andrew J.; Selden, Paul A.; Edwards, Dianne (1990). "Land Animals in the Silurian: Arachnids and Myriapods from Shropshire, England". Science. 250 (4981): 658–61. Bibcode:1990Sci...250..658J. doi:10.1126/science.250.4981.658. PMID 17810866.  ^ DiMichele, William A; Hook, Robert W (1992). "The Silurian". In Behrensmeyer, Anna K. Terrestrial Ecosystems Through Time: Evolutionary Paleoecology of Terrestrial Plants and Animals. pp. 207–10. ISBN 978-0-226-04155-1. 

References[edit]

Emiliani, Cesare. (1992). Planet Earth : Cosmology, Geology, & the Evolution of Life
Life
& the Environment. Cambridge University Press. (Paperback Edition ISBN 0-521-40949-7) Mikulic, DG, DEG Briggs, and J Kluessendorf. 1985. A new exceptionally preserved biota from the Lower Silurian
Silurian
of Wisconsin, USA. Philosophical Transactions of the Royal Society of London, 311B:75-86. Moore, RA, DEG Briggs, SJ Braddy, LI Anderson, DG Mikulic, and J Kluessendorf. 2005. A new synziphosurine (Chelicerata: Xiphosura) from the Late Llandovery
Llandovery
(Silurian) Waukesha Lagerstatte, Wisconsin, USA. Journal of Paleontology:79(2), pp. 242–250. Ogg, Jim; June, 2004, Overview of Global Boundary Stratotype Sections and Points (GSSP's) https://web.archive.org/web/20060716071827/http://www.stratigraphy.org/gssp.htm Original version accessed April 30, 2006, redirected to archive on May 6, 2015.

External links[edit]

Wikisource has original works on the topic: Paleozoic#Silurian

Wikimedia Commons has media related to Silurian.

Palaeos: Silurian UCMP Berkeley: The Silurian Paleoportal: Silurian
Silurian
strata in U.S., state by state USGS: Silurian
Silurian
and Devonian
Devonian
Rocks (U.S.) " International Commission on Stratigraphy (ICS)". Geologic Time Scale 2004. Retrieved September 19, 2005.  Examples of Silurian
Silurian
Fossils GeoWhen Database for the Silurian

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Geologic history of Earth

Cenozoic
Cenozoic
era¹ (present–66.0 Mya)

Quaternary
Quaternary
(present–2.588 Mya)

Holocene
Holocene
(present–11.784 kya) Pleistocene
Pleistocene
(11.784 kya–2.588 Mya)

Neogene
Neogene
(2.588–23.03 Mya)

Pliocene
Pliocene
(2.588–5.333 Mya) Miocene
Miocene
(5.333–23.03 Mya)

Paleogene (23.03–66.0 Mya)

Oligocene
Oligocene
(23.03–33.9 Mya) Eocene
Eocene
(33.9–56.0 Mya) Paleocene
Paleocene
(56.0–66.0 Mya)

Mesozoic
Mesozoic
era¹ (66.0–251.902 Mya)

Cretaceous
Cretaceous
(66.0–145.0 Mya)

Late (66.0–100.5 Mya) Early (100.5–145.0 Mya)

Jurassic
Jurassic
(145.0–201.3 Mya)

Late (145.0–163.5 Mya) Middle (163.5–174.1 Mya) Early (174.1–201.3 Mya)

Triassic
Triassic
(201.3–251.902 Mya)

Late (201.3–237 Mya) Middle (237–247.2 Mya) Early (247.2–251.902 Mya)

Paleozoic
Paleozoic
era¹ (251.902–541.0 Mya)

Permian
Permian
(251.902–298.9 Mya)

Lopingian
Lopingian
(251.902–259.8 Mya) Guadalupian
Guadalupian
(259.8–272.3 Mya) Cisuralian
Cisuralian
(272.3–298.9 Mya)

Carboniferous
Carboniferous
(298.9–358.9 Mya)

Pennsylvanian (298.9–323.2 Mya) Mississippian (323.2–358.9 Mya)

Devonian
Devonian
(358.9–419.2 Mya)

Late (358.9–382.7 Mya) Middle (382.7–393.3 Mya) Early (393.3–419.2 Mya)

Silurian
Silurian
(419.2–443.8 Mya)

Pridoli (419.2–423.0 Mya) Ludlow
Ludlow
(423.0–427.4 Mya) Wenlock (427.4–433.4 Mya) Llandovery
Llandovery
(433.4–443.8 Mya)

Ordovician
Ordovician
(443.8–485.4 Mya)

Late (443.8–458.4 Mya) Middle (458.4–470.0 Mya) Early (470.0–485.4 Mya)

Cambrian
Cambrian
(485.4–541.0 Mya)

Furongian (485.4–497 Mya) Series 3 (497–509 Mya) Series 2 (509–521 Mya) Terreneuvian
Terreneuvian
(521–541.0 Mya)

Proterozoic
Proterozoic
eon² (541.0 Mya–2.5 Gya)

Neoproterozoic era (541.0 Mya–1 Gya)

Ediacaran
Ediacaran
(541.0-~635 Mya) Cryogenian (~635-~720 Mya) Tonian (~720 Mya-1 Gya)

Mesoproterozoic era (1–1.6 Gya)

Stenian (1-1.2 Gya) Ectasian (1.2-1.4 Gya) Calymmian (1.4-1.6 Gya)

Paleoproterozoic era (1.6–2.5 Gya)

Statherian (1.6-1.8 Gya) Orosirian
Orosirian
(1.8-2.05 Gya) Rhyacian (2.05-2.3 Gya) Siderian
Siderian
(2.3-2.5 Gya)

Archean
Archean
eon² (2.5–4 Gya)

Eras

Neoarchean (2.5–2.8 Gya) Mesoarchean (2.8–3.2 Gya) Paleoarchean
Paleoarchean
(3.2–3.6 Gya) Eoarchean
Eoarchean
(3.6–4 Gya)

Hadean
Hadean
eon² (4–4.6 Gya)

 

 

kya = thousands years ago. Mya = millions years ago. Gya = billions years ago.¹ = Phanerozoic
Phanerozoic
eon. ² = Precambrian
Precambrian
supereon. Source: (2017/02). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units USGS Retrieved 10 March 2013.

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