Overview

The Silurian is a geologic interval often described as the period Silurian, spanning roughly from about 443 million to 419 million years ago. It follows the Ordovician and precedes the Devonian. As the third period of the Paleozoic era within the Phanerozoic eon, the Silurian is notable for biological recovery after a major extinction and for key steps in the colonization of land.

Environment and geology

Global climate in the Silurian warmed following the glaciation that ended the preceding interval. Sea levels rose and shallow continental shelves became widespread, producing extensive carbonate deposition. Rocks that define the start and end of the Silurian are well identified in the field and by characteristic fossil assemblages, although precise numerical boundaries remain refined as geochronology improves. The period includes named subdivisions such as Llandovery, Wenlock, Ludlow and Pridoli, used by geologists to organize strata and events.

Life and ecosystems

Marine ecosystems rebounded strongly after the End-Ordovician extinction, leading to flourishing reefs formed by corals and sponge-like stromatoporoids, and a diversified fauna of brachiopods, mollusks, trilobites and jawless fish. Notable Silurian organisms include large eurypterids (sea scorpions) and early vertebrates. Terrestrial life made its first substantial advances: small vascular plants and simple lichens and microbial mats began to stabilize soils, and arthropods such as millipede-like myriapods and primitive arachnids appear in the fossil record.

Major geological and biological developments

  • Reef expansion and carbonate platform development across shallow seas.
  • Orogenic activity as continents such as Baltica and Laurentia converged, driving mountain building and changing paleogeography.
  • Early evolution of land plants (small, simple vascular forms) and the first clear evidence of terrestrial animals.
  • Continued diversification of marine invertebrates and early vertebrate lineages.

History of study and significance

The Silurian was first defined in the 19th century based on rock sequences in Britain and has since been recognized worldwide in geologic studies by correlating fossil assemblages and rock types. Its importance lies in bridging the major biotic crisis at the end of the Ordovician and the innovations that preface the Devonian 'Age of Fishes', making it a key interval for understanding the early steps of life onto land and the restructuring of marine ecosystems.

For more on terminology, stratigraphic subdivisions and detailed fossil records, see specialist summaries and regional stratigraphic charts linked from general references (Paleozoic, Phanerozoic sources) and field guides to Silurian sections and fossils (period overview, comparative intervals).

Eon context and the place of the Silurian within Earth history remain central to teaching and research, and its rock records continue to inform models of climate, sea level and early terrestrialization.