Silurian period


Also found in: Dictionary, Thesaurus, Medical.
Related to Silurian period: Permian period, Devonian period, Carboniferous period

See also: Geologic Timescale (table)Geologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
..... Click the link for more information.

Silurian period

(sĭlo͝or`ēən, sī–) [from the Silures, ancient tribe of S Wales, where the period was first studied; named by the British geologist R. I. MurchisonMurchison, Sir Roderick Impey
, 1792–1871, British geologist. He served in the Napoleonic Wars but after the peace turned his attention to science. In the 1830s he undertook the investigation of previously undifferentiated rock strata in Wales and England; as a result of
..... Click the link for more information.
], third period of the Paleozoic eraPaleozoic era
, a major division (era) of geologic time (see Geologic Timescale, table) occurring between 570 to 240 million years ago. It is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (see each listed individually).
..... Click the link for more information.
 of geologic time (see Geologic TimescaleGeologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
..... Click the link for more information.
, table) lasting from 405 to 435 million years ago. The continents in the Silurian period remained much as they had been in the preceding Ordovician periodOrdovician period
[from the Ordovices, ancient tribe of N Wales], second period of the Paleozoic era of geologic time (see Geologic Timescale, table) from 505 to 438 million years ago.
..... Click the link for more information.
, with approximately the same areas being subject to flooding by shallow seas. The earth was relatively tectonically inactive during the Silurian. The Appalachian Mountains, which uplifted during the Ordovician, were being eroded. Large coral reefs and algae were abundant, indicating that warm, shallow seas predominated. Major evaporite basins, including the circular Michigan Basin, showed evidence of subsidence. The transition between the Ordovician and Silurian rocks is not clearly marked in the United States. The Medina sandstone extending from New York to Alabama has been assigned to both periods but is generally considered to be Silurian. Three main series, based on the succession of strata in New York state, are usually distinguished—the lower Silurian (Medinan, or Alexandrian, series), the middle Silurian (Niagaran series), and the upper Silurian (Cayugan series). The early Silurian deposits in the East are commonly sandstone, shale, and conglomerate, comprising erosion products from high-standing mountains; in the West, marine limestone predominates. There were also desert conditions, under which the Salinan "red beds" of the Appalachian area and the salt deposits of New York, Michigan, Ontario, and Ohio were formed. Some areas were later reflooded, depositing Cobleskill and Rondout limestone of New York. The Silurian of the Far West is as yet not well established. In North America, the Silurian ended quietly; however, in the British Isles, Scandinavia, and France, as a result of the Caledonian disturbance, great mountains continued to be thrust up. Economic resources of the Silurian strata, besides salt, are iron ore (near Birmingham, Ala.) and quartz sandstone, used in glass manufacture. Dominating the life of the Silurian were marine invertebrates, including crinoids and cystoids, mollusks, and eurypterids, invertebrates related to crabs and insects. Members of the trilobite family were still numerous; primitive fishes increased in number. Also notable in the Silurian fauna were scorpions, possibly the first animals to live on land and take their oxygen from the air.
References in periodicals archive ?
Until now, the oldest shark remains had hailed from the Silurian period, some 25 million years younger.
Dudley's ancient fossil history dates back 420 million years to the Silurian period.
The fossils come from the city of Ludlow in Shropshire, England, where they were embedded within rocks from Earth's Silurian period, report Andrew J.
13]C excursions followed at the beginning and top of the late Pridoli with a continuation into the Devonian, evidencing that the carbon cyclic development had become labile again by the end of the Silurian Period.
The first land animals appear in the fossil record at the end of the Silurian period and the beginning of the Devonian period, roughly 400 million years ago.
Donald Mikulic of the Illinois State Geological Survey in Champaign and co-workers report in the May 10 SCIENCE on the discovery of 15 different types of soft-bodied animals dating back 430 million years to the Silurian period.
The Ice Age occurred in the Ordovician and Silurian Periods of geological time (part of the Early Palaeozoic Era), an interval that witnessed a major diversification of early marine animals including trilobites and primitive fish as well as the emergence of the first land plants.