Silurian

Silurian
443.8 ± 1.5 – 419.2 ± 3.2 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Map of Earth during the early Silurian, c. 440 Ma
Chronology
−444 — – −442 — – −440 — – −438 — – −436 — – −434 — – −432 — – −430 — – −428 — – −426 — – −424 — – −422 — – −420 — – −418 — Paleozoic Ordovician Silurian Devonian Llandovery Wenlock Ludlow Přídolí Rhuddanian Aeronian Telychian Sheinwoodian Homerian Gorstian Ludfordian             ← Lau event ← Mulde event[1] ← Ireviken event[2] Subdivision of the Silurian according to the ICS, as of 2021.[3] Vertical axis scale: millions of years ago.
Etymology
Name formality	Formal
Synonym(s)	Gotlandian
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Period
Stratigraphic unit	System
First proposed by	Roderick Murchison, 1835
Time span formality	Formal
Lower boundary definition	FAD of the Graptolite Akidograptus ascensus
Lower boundary GSSP	Dob's Linn, Moffat, United Kingdom 55°26′24″N 3°16′12″W / 55.4400°N 3.2700°W / 55.4400; -3.2700
Lower GSSP ratified	1984[4][5]
Upper boundary definition	FAD of the Graptolite Monograptus uniformis
Upper boundary GSSP	Klonk, Czech Republic 49°51′18″N 13°47′31″E / 49.8550°N 13.7920°E / 49.8550; 13.7920
Upper GSSP ratified	1972[6]
Atmospheric and climatic data
Sea level above present day	Around 180 m, with short-term negative excursions[7]

The Silurian (/sɪˈljʊəri.ən, saɪ-/ sih-LURE-ee-ən, sy-)^[8][9][10] 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 Mya.^[11] The 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 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,^[12][13] dikaryan fungi started expanding and diversifying along with glomeromycotan fungi,^[14] and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized.^[15]

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)，^[16] although this corresponded to sharp decline of jawless fish such as conodonts and ostracoderms.