Its use resulted in many letters from scientists and geologists who argued that it was impossible for a reptilian lifeform to have existed in the Silurian period.

* The earlier Doctor Who and the Silurians had resulted in many letters from scientists and geologists who argued that it was impossible for a reptilian lifeform to have existed in the Silurian era.

* Silurian ( Doctor Who ), a fictional race of humanoid reptiles

The Silurian leader Eldane ( Stephen Moore ) recognises that humans and Silurians have the potential to reach some common ground in the future, and allows the Doctor and some of his allies to depart, leaving two humans behind with the Silurians to act as ambassadors to the human race when the Silurians re-awaken in a thousand years.

The older Silurian tells the Doctor how their race retreated underground when they saw the Moon approaching Earth millions of years before.

The Doctor and Liz, meanwhile, repair the reactor, and go to the underground base, where the younger Silurian realises he has been duped into sending his race back to sleep.

In the 1840s fossils of brachiopods and trilobites from the Silurian period were discovered at Woolshed Creek near Duntroon.

The Ordovician, named after the Celtic tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods respectively.

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.

The Ordovician and Silurian periods were warm greenhouse periods, with the highest sea levels of the Paleozoic ( 200 m above today's ); the warm climate was interrupted only by a ~ 30 Ma cool period, the Early Palaeozoic Icehouse, culminating in the Hirnantian glaciation.

The base of the Silurian is set at a major extinction event when 60 % of marine species were wiped out.

During the early Silurian, they developed specialized cells, which were lignified ( or bore similar chemical compounds ) to avoid implosion ; this process coincided with cell death, allowing their innards to be emptied and water to be passed through them.

About 1900, large oil reserves were discovered in Silurian and Devonian carbonate reservoirs in east-central Kentucky.

Many Ordovician, Silurian, and Devonian agnathans were armored with heavy bony-spiky plates.

Later in history more sedimentary rocks were deposited forming the Smyrna Mills Formation during the Silurian, consisting of shales, limestones, and conglomerates.

By the early Silurian, the gills were becoming adapted for filter feeding and during the Devonian and Carboniferous periods siphons first appeared which, with the newly developed muscular foot, allowed the animals to bury themselves deep in the sediment.

Many of the original Silurian stories were novelised.

The Bar Harbor Formation, which is made up predominantly of sands and silts, and Cranberry Island Formation, made up from volcanic ash and magmatic debris, occurred under similar circumstances in the Silurian and Devonian periods, and were deposited on top of the Ellsworth Schist.

The result was the establishment of the Silurian system under which were grouped, for the first time, a remarkable series of formations, each replete with distinctive organic remains other than and very different from those of the other rocks of England.

These researches, together with descriptions of the coalfields and overlying formations in South Wales and the English border counties, were embodied in The Silurian System ( 1839 ).

The chief geological investigation of the last decade of his life was devoted to the Highlands of Scotland, where he wrongly believed he had succeeded in showing that the vast masses of crystalline schists, previously supposed to be part of what used to be termed the Primitive formations, were really not older than the Silurian period, for that underneath them lay beds of limestone and quartzite containing Lower Silurian ( Cambrian ) fossils.

There is an unconformity where Silurian strata were exposed to erosion and are missing.

The accumulations of Old Red Sandstone, laid down from 408 to 370 million years ago, were created as earlier Silurian rocks, uplifted by the formation of Pangaea, eroded and then were deposited into river deltas.

Iapetus closed up completely at the end of the Silurian period ( 443-415 million years ago ) and the Wicklow Mountains were uplifted during the main phase of the Caledonian orogeny at the start of the Devonian period ( 415-358 million years ago ) when the continents of Baltica and Laurentia collided.

Towards the end of the Silurian the Iapetus would have fully closed, and England and Scotland were joined.

Breaking into Quinn's office, the Doctor finds a globe that depicts the Earth's continents, as they were 200 million years ago, which the Doctor identifies as during the Silurian period.

Sedimentary layers laid down between 435 and 408 Ma ( Silurian epoch ) were deformed and metamorphosed into schists, greywackes and quartzites ( such as in the area of Castro Laboreiro ).

They were formed during the Caledonian orogeny of the Silurian period and then rejuvenated in the Hercynian orogeny of the Upper Carboniferous period.

The Shawangunk Conglomerate was deposited over the Martinsburg Shale in thick braided rivers during the Silurian ( about 420 million years ago ); both sequences of sedimentary rock were subsequently deformed and uplifted during the Permian ( about 270 million years ago ).

The first vertebrates appeared in the form of primitive fish, which greatly diversified in the Silurian and Devonian.

Xylem cells are specialised for conduction of water, and first appeared in plants during their transition to land in the Silurian period more than 425 million years ago ( see Cooksonia ).

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.

This class of arthropod is thought to be among the first animals to have colonised land during the Silurian geologic period.

The geologic period Silurian was first described by Roderick Murchison in rocks located in the original lands of the Silures, hence the name.

The first armored agnathans — the Ostracoderms, precursors to the bony fish and hence to the tetrapods ( including humans )— are known from the middle Ordovician, and by the Late Silurian the agnathans had reached the high point of their evolution.

The first sarcopterygians, found in the uppermost Silurian ( ca 418 Ma ), closely resembled the Acanthodians ( the " spiny fish ", a taxon that went extinct at the end of the Paleozoic ).

Sir Roderick Impey Murchison, 1st Baronet KCB DCL FRS FRSE FLS PRGS PBA MRIA ( 22 February 1792 – 22 October 1871 ) was a Scottish geologist who first described and investigated the Silurian system.

Macroscopic remains of true vascular plants are first found in the fossil record during the Silurian Period of the Paleozoic era.

In the first two instances ( Sanquhar and Thornhill ) the Carboniferous sediments lie in hollows worn out of the old Silurian tableland.

* Sir Roderick Murchison KCB FRS, Scottish geologist who first described and investigated the Silurian system.

Since the mechanism is faulty, the younger Silurian will stay awake to operate it and sacrifice his life, while the new leader of the Silurians having orders to return to the area in 50 years and exterminate Humanity as the colony's first order of business.

The two ancient continents moved toward one another through the Cambrian and Ordovician periods, with tectonic folding during the Silurian pushing the first Scottish land above water.

They evolved in the sea at the beginning of the Silurian Period, some 50 million years before the first sharks appeared.

The first identifiable placoderms evolved in the late Silurian ; they began a dramatic decline during the Late Devonian extinctions, and the class was entirely extinct by the end of the Devonian.

Since Alfred Eisenack first recognised and named the group in 1930, the Chitinozoa have proven incredibly useful as a stratigraphic markers in biostratigraphy during the Ordovician, Silurian and Devonian periods.

He discovered secondary ( Cretaceous ) fossils in Queensland in 1860, he was also the first to indicate the presence of Silurian rocks, and to determine the age of the coal-bearing rocks in New South Wales.

creek the Rev W B Clarke first recognised Silurian fossils.

He discovered them around 1844 century and it was the first time that Silurian rocks were identified in Australia, and at the time were the oldest known rocks in Australia.

A new species of Lower Silurian ( middle Llandovery ) phacopsid trilobite, Acaste birminghamensis, was first collected from exposures on Red Mountain

Pterygotus first arose during the Silurian period, and eventually died out during the early to mid-Devonian.

Pterygotus was featured in the Silurian portion of the first episode of the BBC series Walking with Monsters, where it menaced a Brontoscorpio that was pursuing the Devonian jawless fish Cephalaspis.