Silurian is a geologic period and system spanning 24.6 million
years from the end of the
Ordovician Period, at 443.8 million years
ago (Mya), to the beginning of the
Devonian Period, 419.2
Silurian is the shortest period of the Paleozoic
Era. 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 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 was the
diversification of jawed fish 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.
1 History of study
2.5 Regional stages
4 Climate and sea level
5 Flora and fauna
8 External links
History of study
Life timelineThis box:
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(−4540)←Earliest water←Earliest life←Earliest
AgesAxis scale: million years
(See also: Human timeline, and Nature timeline.)
Silurian system was first identified by British geologist Roderick
Murchison, who was examining fossil-bearing sedimentary rock strata in
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
for Wales. This naming does not indicate any correlation between the
occurrence of the
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
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 system including
the contested beds. An early alternative name for the
"Gotlandian" after the strata of the Baltic island of Gotland.
The French geologist Joachim Barrande, building on Murchison's work,
used the term
Silurian in a more comprehensive sense than was
justified by subsequent knowledge. He divided the
Silurian rocks of
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
Bohemia as a classic ground for the study of the earliest
Llandovery Epoch lasted from 443.8 ± 1.5 to 433.4
± 2.8 mya, and is subdivided into three stages: the
Rhuddanian, 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 in Carmarthenshire,
See also: Wenlock (Silurian)
The Wenlock, which lasted from 433.4 ± 1.5 to 427.4
± 2.8 mya, is subdivided into the
430.5 million years ago) and
Homerian ages. It is named after
Wenlock Edge in Shropshire, England. During the Wenlock, the
oldest-known tracheophytes of the genus Cooksonia, appear. The
complexity of slightly later
Gondwana plants like Baragwanathia, which
resembled a modern clubmoss, indicates a much longer history for
vascular plants, extending into the early
Silurian or even
Ordovician. The first terrestrial animals
also appear in the Wenlock, represented by air-breathing millipedes
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 (and neighbouring Ludford) in Shropshire,
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
Slivenec in the Czech Republic.
Přídolí is the old name of a cadastral field area.
In North America a different suite of regional stages is sometimes
Silurian – Ludlow)
Lockportian (Middle Silurian: late Wenlock)
Tonawandan (Middle Silurian: early Wenlock)
Ontarian (Early Silurian: late Llandovery)
Alexandrian (Earliest Silurian: early Llandovery)
Estonia the following suite of regional stages is used:
Ohessaare stage (Late
Silurian – early Přídolí)
Kaugatuma stage (Late
Silurian – late Přídolí)
Kuressaare stage (Late
Silurian – late Ludlow)
Paadla stage (Late
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)
Silurian boundary on Hovedøya, Norway, showing brownish
Ordovician mudstone and later dark deep-water
Silurian shale. The
layers have been overturned by the Caledonian orogeny.
With the supercontinent
Gondwana covering the equator and much of the
southern hemisphere, a large ocean occupied most of the northern half
of the globe. The high sea levels of the
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
During the Silurian,
Gondwana continued a slow southward drift to high
southern latitudes, but there is evidence that the
were less extensive than those of the late-
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 sediments overlie eroded Ordovician
sediments, forming an unconformity. The continents of Avalonia,
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 strata in northern Ohio
The vast ocean of
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 (a narrow seaway
Avalonia and Laurentia), and the newly formed Ural Ocean.
Climate and sea level
Silurian period enjoyed relatively stable and warm temperatures,
in contrast with the extreme glaciations of the
Ordovician before it,
and the extreme heat of the ensuing Devonian. Sea levels
rose from their
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
sea level was probably around 140 m higher than the lowest level
During this period, the
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 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
Devonian boundary, the climate became warmer.[citation
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. The Ireviken event,
Mulde event and Lau
event each represent isotopic excursions following a minor mass
extinction and associated with rapid sea-level change, in
addition to the larger extinction at the end of the
Silurian. 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.
Flora and fauna
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
Earth until it diversified in the Devonian.
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 period. The earliest-known representatives of
this group are Cooksonia. Most of the sediments containing Cooksonia
are marine in nature. Preferred habitats were likely along rivers and
Baragwanathia appears to be almost as old, dating to the
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,
Canada and China.
Eohostimella heathana is an
early, probably terrestrial, "plant" known from compression
fossils of early
Silurian (Llandovery) age.
The chemistry of its fossils is similar to that of fossilised vascular
plants, rather than algae.
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
Silurian seas of North America; many of their fossils have
been found in New York state. Leeches also made their appearance
Silurian Period. Brachiopods, bryozoa, molluscs,
hederelloids, tentaculitoids, crinoids and trilobites were abundant
and diverse. Endobiotic symbionts were common
in the corals and stromatoporoids.
Reef abundance was patchy; sometimes fossils are frequent but at other
points are virtually absent from the rock record.
The earliest-known animals fully adapted to terrestrial conditions
appear during the Mid-Silurian, including the millipede
Pneumodesmus. Some evidence also suggests the presence of
predatory trigonotarbid arachnoids and myriapods in Late Silurian
facies. Predatory invertebrates would indicate that simple
food webs were in place that included non-predatory prey animals.
Extrapolating back from Early
Devonian biota, Andrew Jeram et al. in
1990 suggested a food web based on as-yet-undiscovered
detritivores and grazers on micro-organisms.
Cooksonia, the earliest vascular plant, middle Silurian
Silurian sea bed fossils collected from Wren's Nest Nature Reserve,
Crinoid fragments in a
Silurian (Pridoli) limestone (Saaremaa,
Silurian sea bed fossils collected from Wren's Nest Nature Reserve,
Artist's impression of
Silurian underwater fauna
Eurypterus, a common Upper
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.
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Original version accessed April 30, 2006, redirected to archive on May
Wikisource has original works on the topic: Paleozoic#Silurian
Wikimedia Commons has media related to Silurian.
UCMP Berkeley: The Silurian
Silurian strata in U.S., state by state
Devonian Rocks (U.S.)
International Commission on Stratigraphy (ICS)". Geologic Time Scale
2004. Retrieved September 19, 2005.
GeoWhen Database for the Silurian
Silurian (Chronostratography scale)
vteGeological history of EarthCenozoic
Quaternary (present–2.588 Mya)
Holocene (present–11.784 kya)
Pleistocene (11.784 kya–2.588 Mya)
Neogene (2.588–23.03 Mya)
Pliocene (2.588–5.333 Mya)
Miocene (5.333–23.03 Mya)
Paleogene (23.03–66.0 Mya)
Oligocene (23.03–33.9 Mya)
Eocene (33.9–56.0 Mya)
Paleocene (56.0–66.0 Mya)
Mesozoic era(66.0–251.902 Mya)
Cretaceous (66.0–145.0 Mya)
Late (66.0–100.5 Mya)
Early (100.5–145.0 Mya)
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 (201.3–251.902 Mya)
Late (201.3–237 Mya)
Middle (237–247.2 Mya)
Early (247.2–251.902 Mya)
Paleozoic era(251.902–541.0 Mya)
Permian (251.902–298.9 Mya)
Lopingian (251.902–259.8 Mya)
Guadalupian (259.8–272.3 Mya)
Cisuralian (272.3–298.9 Mya)
Carboniferous (298.9–358.9 Mya)
Pennsylvanian (298.9–323.2 Mya)
Mississippian (323.2–358.9 Mya)
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 (419.2–443.8 Mya)
Pridoli (419.2–423.0 Mya)
Ludlow (423.0–427.4 Mya)
Wenlock (427.4–433.4 Mya)
Llandovery (433.4–443.8 Mya)
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 (485.4–541.0 Mya)
Furongian (485.4–497 Mya)
Miaolingian (497–509 Mya)
Series 2 (509–521 Mya)
Terreneuvian (521–541.0 Mya)
Proterozoic eon(541.0 Mya–2.5 Gya)
Neoproterozoic era (541.0 Mya–1
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 (1.8–2.05 Gya)
Rhyacian (2.05–2.3 Gya)
Siderian (2.3–2.5 Gya)
Archean eon (2.5–4 Gya)Eras
Neoarchean (2.5–2.8 Gya)
Mesoarchean (2.8–3.2 Gya)
Paleoarchean (3.2–3.6 Gya)
Eoarchean (3.6–4 Gya)
Hadean eon (4–4.6 Gya) kya = thousands years ago. Mya =
millions years ago. Gya = billions years ago.
See also: Geologic time scale,