The Silurian was described in the 1830s by Englishman Sir Roderick Impey Murchison after rock formations in South Wales. The period was named after a Celtic tribe, the Silures, that lived around regions of the current Welsh-English border.

Paleogeography

Throughout the Silurian, the Gondwana continent continued to move southward. Present-day South-West Africa was located near the South Pole, while the smaller continents gathered around the equator and the tropics.

The end of the Silurian is marked by the collision of the Laurentia, Baltica, and Avalonia continents and the closure of the Iapetus Ocean between them. A new large continent was created, known under various names: Laurosia, Laurussia, Euroamerica, or the "Old Red" continent (after the colour of the sandstone formed in that region). This event is called the Caledonian Orogeny, and it led to the formation of mountain ranges stretching through Europe, Greenland, to North America.

Climate

The Silurian was a transitional period between the cold Late Ordovician and the hot Devonian. The warm climate caused the melting of glaciers, which led to the rise of global sea levels.

Life on Earth

Reefs

Reefs were formed by corals, sponges (stromatoporoids), bryozoans, and coralline algae that used structural mineral substances in their cells.

Graptolites

Silurian was a time of graptolite renissance. The genus Mongraptus, a common cosmopolitan graptolite of that time, split into many species that are useful index fossils. Silurian graptolite shales are of interest to geologists looking for hydrocarbon deposits.

Origin of jaws

In vertebrates, the development of jaws was a completely new invention. They evolved from gill arches and took on new functions. Hard mouthparts were more efficient for feeding and began to displace more primitive types. The oldest vertebrates with jaws were armoured fishes.

Life on land

The first vascular plants, rhyniophytes, appeared at the beginning of the Silurian. They did not have leaves, roots, the ability to expand in width, or the ability to conduct water via the stem. Early terrestrial floral communities homed the early faunal land life. Early terrestrial animals were millipede-like animals that fed on dead organic matter, predated on by relatives of modern centipedes.

Do you know...

The sea level in the Silurian was 200 meters higher than today.