Life takes root on land
Silurian
Paleozoic Era · 443.8 – 419.2 million years ago
The Silurian Period lasted from about 443.8 to 419.2 million years ago, roughly 25 million years, making it the shortest period of the Paleozoic. It began as life recovered from the end-Ordovician mass extinction and saw the first vascular plants take hold on land.
In the seas, coral reefs spread across warm tropical shelves, jawed fish diversified and sea scorpions grew to impressive sizes. Meanwhile, colliding continents raised the Caledonian mountains, whose worn-down roots still shape the landscapes of Scotland, Norway and eastern North America.
Key facts
- Began
- 443.8 MaMillion years ago
- Ended
- 419.2 MaMillion years ago
- Duration
- 24.6 million years
- Era
- Paleozoic“Ancient life”
- Global temperature
- ~18°CRoughly 14–21°C · today 14.5°C
- Plants on land
- Mosses & liverworts
- Atmospheric CO₂
- High, perhaps ~3,000–4,500 ppm; poorly constrained
- Oxygen
- Probably approaching modern levels late in the period
- Sea level
- High, with broad tropical seas over continents
- Continents
- Laurentia, Baltica and Avalonia merge; Gondwana in south
- Signature life
- Cooksonia, eurypterids, coral reefs, early jawed fish
- Began with
- Recovery from the end-Ordovician extinction
- Ended with
- No mass extinction; gradual transition to Devonian
Ages follow the International Chronostratigraphic Chart (ICS). Global temperatures are rough reconstructions after Scotese et al. (2021); ancient CO₂, oxygen and sea-level values carry large uncertainties.
Epochs of the Silurian
- Llandovery443.8 Ma – 433.4 Ma
- Wenlock433.4 Ma – 427.4 Ma
- Ludlow427.4 Ma – 423 Ma
- Pridoli423 Ma – 419.2 Ma
Continents and oceans
The defining event of the Silurian was a slow continental collision. Laurentia, Baltica and Avalonia converged as the Iapetus Ocean closed, welding together to form Laurussia, also called Euramerica.
The collision built the Caledonian mountain belt, stretching through what are now Scandinavia, Scotland, Ireland, Greenland and the northern Appalachians. To the south, Gondwana still covered the South Pole, separated from Laurussia by the widening Rheic Ocean.
Much of Laurussia lay in the tropics and was flooded by shallow, warm seas. Reefs grew along their edges, and in some restricted basins, such as the Michigan Basin, evaporation left thick deposits of salt.
Climate and atmosphere
After the Hirnantian ice age, the climate warmed into a largely greenhouse state, although glacial deposits in South America show that some ice persisted in the early Silurian. Carbon dioxide was probably several times higher than today, but estimates for this period are particularly uncertain.
The Silurian was less stable than it once seemed. Several sharp swings in the carbon cycle, including the Ireviken and Lau events, coincided with extinctions among conodonts, graptolites and reef animals, and the Lau event produced one of the largest carbon-isotope shifts of the past 500 million years.
Life in the Silurian
Silurian life rebuilt quickly after the Ordovician extinction. The seas filled with reef builders and new kinds of fish, while plants and small arthropods began to establish the first true land ecosystems.
On land
Cooksonia, a plant just a few centimetres tall with forked stems tipped by spore capsules, is among the oldest known vascular plants, from around 430 million years ago. By the late Silurian, millipedes, early centipedes and spider-like arachnids lived among these tiny plants.
Reefs
Tabulate and rugose corals, stromatoporoid sponges and bryozoans built extensive reefs in tropical seas. Reef limestones of this age form Wenlock Edge in England and much of the island of Gotland in Sweden.
Sea scorpions
Eurypterids, or sea scorpions, thrived in coastal and brackish waters. Eurypterus is common in rocks of New York State, and pterygotids such as Acutiramus grew to perhaps 2 metres long, among the largest arthropods ever.
Jawed fish
Jawed fish diversified, including spiny acanthodians and armoured placoderms. Entelognathus, a placoderm from China, has jaw bones resembling our own, and Guiyu, from about 423 million years ago, is one of the oldest well-preserved bony fish.
Timeline of key events
- 443.8 Ma
Silurian begins
The period starts at Dob's Linn, Scotland, as marine life recovers from the end-Ordovician extinction.
- 433 Ma
Ireviken event
A carbon-cycle disturbance near the start of the Wenlock causes extinctions among conodonts and graptolites.
- 430 Ma
Cooksonia on land
Some of the earliest known vascular plants grow along damp shorelines and river banks.
- 425 Ma
Caledonian collision peaks
Baltica and Laurentia collide head-on, raising high mountains across Scandinavia and Greenland.
- 424 Ma
Lau event
One of the largest carbon-isotope excursions of the Phanerozoic coincides with marine extinctions.
- 423 Ma
Early bony fish
Guiyu, one of the oldest well-preserved bony fish, lives in the seas of what is now China.
- 419.2 Ma
Transition to the Devonian
The appearance of the graptolite Monograptus uniformis at Klonk, Czech Republic, marks the start of the Devonian.
How the Silurian ended
The Silurian ended quietly, without a mass extinction. Its boundary with the Devonian, about 419.2 million years ago, is defined at Klonk in the Czech Republic by the first appearance of the graptolite Monograptus uniformis.
As the Caledonian mountains rose, rivers began carrying red sand and gravel into nearby basins. These deposits, the Old Red Sandstone, span the Silurian–Devonian transition and record a land surface increasingly shaped by plants.
Where to see Silurian fossils
The Silurian was first defined in the Welsh Borderland, and Wenlock Edge and Dudley in England remain classic places to see reef fossils and trilobites. The Herefordshire Lagerstätte preserves tiny animals in three dimensions, and the island of Gotland in Sweden offers spectacular fossil reefs.
In North America, the Bertie Group of New York and Ontario is renowned for eurypterids, and the Niagara Escarpment exposes Silurian reef rocks. The Waukesha Biota of Wisconsin preserves rare soft-bodied animals.
Surprising facts about the Silurian
- The oldest known charcoal comes from late Silurian rocks, showing that wildfires were already burning and that oxygen was high enough to sustain them.
- A Silurian trilobite, Calymene blumenbachii, was so common in the limestone quarries of Dudley, England, that it became known as the 'Dudley bug' and appears on the town's coat of arms.
- The Silurian–Devonian boundary at Klonk, Czech Republic, was the very first golden spike (GSSP) ever ratified, in 1972, setting the model for defining geological time worldwide.
- The name Silurian comes from the Silures, a tribe in Roman-era Wales, and was introduced by Roderick Murchison in 1835.
- Some Silurian sea scorpions were larger than a human, making them among the biggest arthropods that have ever lived.
- Cooksonia had no leaves or roots; it photosynthesised through its slender green stems, which branched in simple Y-shapes.
Where it sits in deep time
The globe beside this article shows Earth 430 million years ago, reconstructed from the PALEOMAP paleo-elevation models. Step to another period and watch the continents drift into place.