Silurian

The Silurian is a time in Earth's history. It lasted for 23.5 million years, from 443.1 million years ago to 419.62 million years ago. It was the third and shortest time period of the Paleozoic Era, part of the larger Phanerozoic Eon. Scientists study special layers of rock to learn when this period began and ended.

One big change during the Silurian was the first time plants grew on land. These early vascular plants were different from simpler plants and changed life on Earth. Fungi and small creatures like spiders, millipedes, and insects also began living on land.

Many new kinds of fish appeared in the oceans during the Silurian. These included types like placoderms, acanthodians, and bony fish. Some older kinds of fish, like those without jaws, became less common.

History of study

The Silurian system was first found by a Scottish geologist named Roderick Murchison. He looked at rocks with fossils in south Wales in the early 1830s. He named these rocks after a Celtic tribe in Wales called the Silures. His friend Adam Sedgwick gave him the idea. Sedgwick had already named another time period the Cambrian after a Latin name for Wales.

In 1835, Murchison and Sedgwick told everyone about the Silurian and Cambrian systems. This helped make the modern geological time scale. Later, a scientist named Charles Lapworth helped solve problems by making a new system called the Ordovician.

A French geologist named Joachim Barrande studied Silurian rocks in Bohemia. He split the rocks into different stages. His work made Bohemia a key place for learning about early Silurian fossils.

Subdivisions

Paleogeography

During the Silurian time, a huge landmass called Gondwana sat near the equator. A big ocean covered most of the north. The high water levels and flat lands made many island chains and different environments.

Gondwana slowly moved toward the south, but there was less ice than before. As the ice melted, sea levels rose and covered older land layers. Three land areas—Avalonia, Baltica, and Laurentia—moved closer to the equator, beginning to form a new big landmass called Euramerica.

When early Europe bumped into North America, it pushed up lots of rocks, forming mountains from New York State through Europe and Greenland to Norway. By the end of this time, sea levels fell, leaving dry areas, and the new mountains wore down quickly. The big ocean Panthalassa covered most of the north, with some smaller oceans around.

Climate and sea level

The Silurian period used to be thought of as having steady, warm weather. But we now know the climate changed a lot during this time. The sea levels rose during the first half of the Silurian and then fell for the rest of it. There were fifteen times when the sea rose above the edge of the land.

The Earth was in a warm phase with lots of a gas called CO₂. Glaciers melted away near the South Pole. Layers of broken shells show that strong storms happened often because of the warm oceans.

Flora and fauna

The Silurian period was when life on land began to grow. Scientists think it was a time to recover after a big change in the world before this. During the Silurian, we started to see tiny forests made of moss-like plants and other simple plants along lakes and streams. This was the start of a big change called the Silurian-Devonian Terrestrial Revolution.

The first plants with special tissues that carry water and food appeared in the second half of the Silurian. One of the earliest known plants was Cooksonia. Most places where we find Cooksonia fossils are in the ocean, but they probably lived near rivers and streams. Another plant, Baragwanathia, had branching stems and needle-like leaves. Fossils of this plant have been found in Australia, Canada, and China.

We also know about some of the first animals that lived on land from the Silurian. The oldest known millipede, Kampecaris obanensis, lived in the late Silurian. There were also other small animals like centipedes and spider-like creatures. In the oceans, the first bony fish appeared. These fish had bony scales and could move their jaws. Sea scorpions, called eurypterids, swam in the shallow seas and lakes. Many different kinds of sea creatures lived during this time, including brachiopods, bryozoans, bivalves, chitons, and trilobites. Corals and other reef animals also began to appear and grow in some places.