Silurian

EtymologyName formalityFormalSynonym(s)Gotlandian
Usage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitPeriodStratigraphic unitSystemFirst proposed byRoderick Murchison, 1835Time span formalityFormalLower boundary definitionFAD of the GraptoliteLower boundary GSSPDob's Linn, Moffat, United Kingdom
55°26′24″N3°16′12″W / 55.4400°N 3.2700°W / 55.4400; -3.2700Lower GSSP ratified1984Upper boundary definitionFAD of the Graptolite Monograptus uniformisUpper boundary GSSPKlonk, Czech Republic
49°51′18″N13°47′31″E / 49.8550°N 13.7920°E / 49.8550; 13.7920Upper GSSP ratified1972Atmospheric and climatic dataSea level above present dayAround 180 m, with short-term negative excursions

The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at 443.1 Ma (million years ago) to the beginning of the Devonian Period, 419.62 Ma. The Silurian is the third and shortest period of the Paleozoic Era, and the third of twelve periods of the Phanerozoic Eon. 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 a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.

One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized.

Another significant evolutionary milestone during the Silurian was the diversification of jawed fish, which include placoderms, acanthodians (which gave rise to cartilaginous fish) and osteichthyan (bony fish, further divided into lobe-finned and ray-finned fishes), although this corresponded to sharp decline of jawless fish such as conodonts and ostracoderms.