Silurian Period 443.7–416 million years ago PreЄ Є O S D C P T J K Pg N
Mean atmospheric O2 content over period duration	ca. 14 Vol %[1] (70 % of modern level)
Mean atmospheric CO2 content over period duration	ca. 4500 ppm[2] (16 times pre-industrial level)
Mean surface temperature over period duration	ca. 17 °C[3] (3 °C above modern level)
Sea level (above present day)	Around 180m, with short-term negative excursions[4]

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 million years ago (mya), to the beginning of the Devonian Period, about 416.0 ± 2.8 mya (ICS, 2004^[5]). 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 major extinction event when 60% of marine species were wiped out. See Ordovician-Silurian extinction events.

A significant evolutionary milestone during the Silurian was the appearance of jawed and bony fish. Life also began to appear on land in the form of small, moss-like, vascular plants which grew beside lakes, streams, and coastlines. However, terrestrial life would not greatly diversify and impact the landscape until the Devonian.

History of study[link]

The Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, following the convention his friend Adam Sedgwick had established for the Cambrian. In 1835 the two men presented a joint paper, under the title On the Silurian and 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 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 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 established Bohemia as a classic ground for the study of the earliest fossils.

Subdivisions[link]

Llandovery[link]

The Llandovery epoch lasted from 443.7 ± 1.5 to 428.2 ± 2.8 mya, and is subdivided into three stages: the Rhuddanian,^[8] lasting until 439 million years ago, the Aeronian, lasting to 436 million years ago, and the Telychian. The epoch is named for the town of Llandovery in Carmarthenshire, Wales.

Wenlock[link]

The Wenlock, which lasted from 428.2 ± 1.5 to 422.9 ± 2.8 mya, is subdivided into the Sheinwoodian (to 426.2 million years ago) and Homerian ages. It is named after the Wenlock Edge in Shropshire, England. During the Wenlock, the oldest known tracheophytes of the genus Cooksonia, appear. The complexity of slightly younger Gondwana plants like Baragwanathia indicates either a much longer history for vascular plants, perhaps extending into the early Silurian or even Ordovician. See Evolutionary history of plants.

Ludlow[link]

The Ludlow, lasting from 422.9 ± 1.5 to 418.7 ± 2.8 mya, comprises the Gorstian stage, lasting until 421.3 million years ago, and the Ludfordian stage. It is named for the town of Ludlow in Shropshire, England.

[edit] Přídolí

The Pridoli, lasting from 418.7 ± 1.5 to 416 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at natural reserve Homolka a Přídolí near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area.^[9]

Regional stages[link]

In North America a different suite of regional stages is sometimes used:

• Cayugan (Late Silurian - Ludlow)
• Lockportian (middle Silurian: late Wenlock)
• Tonawandan (middle Silurian: early Wenlock)
• Ontarian (Early Silurian: late Llandovery)
• Alexandrian (earliest Silurian: early Llandovery)

Geography[link]

Ordovician-Silurian boundary exposed on Hovedøya, Norway, showing the very marked difference between the light gray Ordovician calcareous sandstone and brown Silurian mudstone. The layers have been inverted (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.^[10] 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 settings.^[10]

During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps 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, Baltica, and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica.

Fossilised Late Silurian shallow sea floor, on display in Bristol City Museum, Bristol, England. From the Wenlock epoch, in the Wenlock limestone, Dudley, West Midlands, England.

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 in a basin 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 strata, leaving traces in the Silurian strata of northern Ohio and Indiana.

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, a seaway of the Iapetus Ocean (now in between Avalonia and Laurentia), and the newly formed Ural Ocean.

Climate and sea level[link]

The 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.^[10] 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 reached.^[10]

During this period, the Earth entered a long warm greenhouse phase, 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 in the Silurian-Devonian boundary, the climate became warmer.

Perturbations[link]

End of Silurian extinction. Click on the picture for more information

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.^[10] The Ireviken event, Mulde event and Lau event each represent isotopic excursions following a minor mass extinction^[11] and associated with rapid sea-level change, in addition to the larger extinction at the end of the Silurian.^[10] Each home 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.^[10]

Flora and fauna[link]

Artist's impression of Silurian fish

Cooksonia, the earliest vascular plant, middle Silurian

The Silurian was the first period to see macrofossils of extensive terrestrial biota, in the form of moss forests along lakes and streams. However, the land fauna did not have a major impact on the Earth until it diversified in the Devonian.^[10]

The first fossil records of vascular plants, that is, land plants with tissues that carry food, appeared in the second half of the Silurian period. The earliest known representatives of this group are the Cooksonia (mostly from the northern hemisphere) and Baragwanathia (from Australia). A primitive Silurian land plant with xylem and phloem but no differentiation in root, stem or leaf, was much-branched Psilophyton, reproducing by spores and breathing through stomata on every surface, and probably photosynthesizing in every tissue exposed to light. Rhyniophyta and primitive lycopods were other land plants that first appear during this period. Neither mosses nor the earliest vascular plants had deep roots. Silurian rocks often have a brownish tint, possibly a result of extensive erosion of the early soils.

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 seas of North America; many of their fossils have been found in New York state. Leeches also made their appearance during the Silurian Period. Brachiopods, bryozoa, molluscs, hederelloids and trilobites were abundant and diverse.

Reef abundance was patchy; sometimes they were everywhere, but at other points they are virtually absent from the rock record.^[10]

Some evidence 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^[12] suggested a food web based on as yet undiscovered detritivores and grazers on microorganisms.^[13]

Notes[link]

References[link]

• Emiliani, Cesare. (1992). Planet Earth : Cosmology, Geology, & the Evolution of 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 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 (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) http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.

External links[link]

Wikimedia Commons has media related to: Silurian

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

Gary Russell

Gary James Russell (born 18 September 1963) is a freelance writer and former child actor. As a writer, he is best known for his work in connection with the television series Doctor Who and its spin-offs in other media. As an actor he is best known for playing Dick Kirrin in the British 1978 television series, The Famous Five.

Biography[link]

Russell was born in Maidenhead, Berkshire, England, UK^{[citation needed]} and currently lives in Cardiff.^{[citation needed]} His on-screen acting career ranged from leading roles in the BBC's adaptation of E. Nesbit's novel The Phoenix and the Carpet and ITV's adaptations of Enid Blyton's Famous Five novels (as Dick) to a very minor walk-on part in the James Bond movie Octopussy.^{[citation needed]} He has also appeared on stage.^{[citation needed]} He was editor of Doctor Who Magazine between 1992 and 1995. He was the producer for the Doctor Who licensed audio drama tie-ins at Big Finish Productions from its inception in 1998 until July 2006, when he stepped down^[1] to work for BBC Wales on Doctor Who and Torchwood.^[2] He has written a number of Doctor Who spin-off novels and in 2000 co-wrote with executive producer Philip Segal the book Doctor Who: Regeneration (HarperCollins, ISBN 0-00-710591-6), the making-of book of the 1996 Doctor Who television movie, as well as the TV movie's novelisation in 1996.

He wrote The Art of The Lord of the Rings, which was also published as three separate books (one for each film), and contributed to Gollum: How We Made Movie Magic with Andy Serkis. His behind-the-scenes book Doctor Who: The Inside Story was published in October 2006, coinciding with his joining the Doctor Who production team. His most recent reference work was also for Doctor Who; published in 2007 by BBC Books, The Doctor Who Encyclopedia is a guide to the current Doctor Who series (2005–present). In 2007, he directed the animated mini series "The Infinite Quest", which tied in with the 2007 television series of Doctor Who.

As of 2011/2012, having left BBC Wales, he has returned to Big Finish to produce the Bernice Summerfield audios and the Gallifrey audios.^[3]

Filmography[link]

• The Airzone Solution (1993) (V)
• Octopussy (1983)
• Schoolgirl Chums (1982) TV Special
• A Shocking Accident (1982)
• Dark Towers (1980) TV Series
• The Famous Five (1978) TV Series
• The Phoenix and the Carpet (1976) (mini) TV Series

Selected bibliography[link]

Comics[link]

• Doctor Who (in Doctor Who Magazine #173, 235-237, 1991, 1996, and in Radio Times issues dated 1 June 1996–2 March 1997)

[edit] IDW Doctor Who comic book

At the 2007 San Diego Comic Con, IDW Publishing announced their intention to publish a new series of Doctor Who comics, which will follow the adventures of the Tenth Doctor and Martha Jones. The first six issues of this series, later collected as Agent Provocateur, were scripted by Russell and published in early 2008. The next run was handled by Tony Lee, as Russell has informally retired from writing original Doctor Who fiction for the rest of his duration at BBC Wales.^[4]

Novels[link]

• Virgin New Adventures:
  • Legacy
  • Deadfall

• Virgin Missing Adventures:
  • Invasion of the Cat-People
  • The Scales of Injustice

• Eighth Doctor Adventures:
  • Placebo Effect

• Past Doctor Adventures:
  • Business Unusual
  • Divided Loyalties
  • Instruments of Darkness
  • Spiral Scratch

• New Series Adventures:
  • Beautiful Chaos
  • The Glamour Chase

• Torchwood:
  • The Twilight Streets

References[link]

External links[link]

• Gary Russell at the Internet Movie Database
• Scales of Injustice E-book on the BBC website
• Interview with Russell on the BBC Doctor Who website
• Interview with Russell in the Pantechnicon Magazine
• Gary Russell at the Internet Speculative Fiction Database

Karen Gillan
Karen Gillan at the San Diego Comic-Con International in July 2011
Born	Karen Sheila Gillan (1987-11-28) 28 November 1987 (age 24) Inverness, Scotland
Occupation	Actress, former model
Years active	2006–present

Karen Sheila Gillan (born 28 November 1987) is a Scottish actress and former model who is mostly known for her portrayal of Amy Pond in the British science fiction series Doctor Who.

Early life[link]

Gillan was born and brought up in Inverness, Scotland.^[1] Her father, Raymond John Gillan, a Day Centre Manager, and mother, Marie Gillan née Paterson, live in Kinmylies. She learned to play the piano when she was seven.^[2] She has no brothers or sisters.^[3] At a young age, she developed a love for acting, joining several local youth theatre groups and taking part in a wide range of productions at her school, Charleston Academy.^[2] When she was sixteen, Gillan decided to use her interest in acting, studying at Edinburgh's Telford College. Later, she got a place at the Italia Conti Academy of Theatre Arts drama school in London on the BA (Hons) Acting degree course.^[4] Gillan moved to London when she was 18 to study at drama school.^[5]

Career[link]

Modelling[link]

Before Gillan became an actress, she was scouted by a modelling agency.^[6]

Gillan worked as a model in 2007's London Fashion Week for designer Allegra Hicks' autumn/winter catwalk show^[6] and the launch party of Nicola Roberts' Dainty Doll Make-Up Range. This was shown in Roberts' episode of the documentary, The Passions of Girls Aloud^{[citation needed]} which premiered on 4 April 2008. Gillan has said she wouldn't give up her acting career to return back to modelling. She stated that she enjoyed modelling but acting was always her main interest and goal.^[7]

Acting[link]

Karen Gillan with Matt Smith, promoting Series 5 of Doctor Who

Gillan's early television acting career included guest appearances on several drama series, with her first ongoing role being a two-year stint as a member of the ensemble cast of the sketch comedy series The Kevin Bishop Show in which she played multiple characters, as well as celebrities such as Katy Perry and Angelina Jolie. She appeared in Channel 4's 'Stacked'; she had the part of Ginny.^[2] Gillan also appeared on TV in a leading role in a horror project entitled The Well, which was broadcast as a series of episodic short films on BBC Two, and then later also as a web series on BBC.co.uk. Part of the BBC's multimedia "switch" programming, the short episodes interconnect with online games that further explore the environments presented in the series.^[8]

She was cast for the role of the Eleventh Doctor's first companion, Amy Pond, on the British sci-fi series Doctor Who in May 2009. She made her first on-screen appearance as Amy Pond in "The Eleventh Hour" with her cousin Caitlin Blackwood portraying a young Amy Pond.^[9][10][11] She was confirmed in Issue 420 of the Doctor Who Magazine to be appearing in the 2011 series. Gillan had appeared in Doctor Who once before in the 2008 episode "The Fires of Pompeii" in the role of a Soothsayer.^[6]

Gillan made her first theatre appearance playing the role of Shirley in John Osborne's play Inadmissible Evidence along with Douglas Hodge.^[12] The play debuted at the Donmar Warehouse on 16 October 2011.^[12]

During August 2011, it was announced Gillan will star in an indie comedy called Not Another Happy Ending along with Emun Elliott.^[13] Filming will take place some time in 2012.^[13]

During an interview at the 2011 San Diego Comic-Con, Gillan revealed she will be returning to Doctor Who for its seventh series.^[14] On 15 December 2011, it was announced Gillan and Arthur Darvill (Rory Williams) would be leaving Doctor Who during the seventh series in 2012.^[15] On 26 January 2012 Karen Gillan played the part of supermodel Jean Shrimpton in the BBC Four film, We'll Take Manhattan which told the story of Shrimpton's relationship with the photographer David Bailey.^[16][17]

She has also been cast as Brittney in a re-working of Shakespeare's Romeo and Juliet called Romeo & Brittney by David Baddiel.^[18][19]

Charity work[link]

In 2011 Gillan helped to promote Fashion Targets Breast Cancer (FTBC)^[20] and also helped celebrate the opening of Squirrel Ward in Great Ormond Street Hospital.^[21]

Filmography[link]

Television

Feature films

Theatre

Self

Video games

Awards[link]

References[link]

External links[link]

Wikimedia Commons has media related to: Karen Gillan

• Karen Gillan at the Internet Movie Database