Llandovery Epoch

The Llandovery Epoch, also called the Early Silurian, was a time that started about 443.1 million years ago and ended around 432.9 million years ago. It was the first part of the Silurian Period in Earth's history. This time came right after the Ordovician-Silurian extinction events. Many plants and animals disappeared, changing the world’s ecosystems.

During the Llandovery Epoch, reefs started to grow in the oceans. These reefs were made by ancient animals like corals. They kept growing into the Devonian Period. But when water got too warm, many corals died because their tiny plant friends could not survive.

The Llandovery Epoch ended with an event called the Ireviken event. This event caused many trilobites, sea creatures with hard shells, to disappear. It also lowered the number of conodonts, small fish-like animals. These changes helped shape life on Earth for millions of years.

Beginning of Silurian

The end of the Ordovician–Silurian extinction event happened when melting glaciers raised sea levels, and the seas then stabilized. As the seas came back, life started to grow again, and many animal groups came back too.

After this big loss of species, communities in the Silurian were simpler at first. The animals that survived could be found all over the world, which was different from before. Even though these events did not change life as much as later extinctions, many species still disappeared quickly, changing the world’s plant and animal life.

The epoch is named after Llandovery in Wales. The exact start of the Silurian is marked by rock layers at Dob's Linn in southern Scotland. These layers help scientists learn when this important time in Earth’s history began.

Subdivisions

The Llandovery Epoch has three main stages: Rhuddanian, Aeronian, and Telychian.

In some areas, like North America and Estonia, these stages have different names. In North America, they are called Ontarian and Alexandrian. In Estonia, they are called Adavere, Raikküla, and Juuru.

Palaeontology

Spores and tiny parts of plants have been found in China and Pennsylvania. During the Llandovery Epoch, some plants began to move to land areas. The earliest known plants with tubes inside, like Cooksonia, appeared a little later.

One interesting fossil from this time is Parioscorpio venator. At first, people thought it might be the earliest animal on land, maybe a scorpion. But later studies showed it was probably a sea animal.

Reef expansion

Barrier reef systems covered more of the ocean floor and grew even in places far from the equator. Tiny plants inside corals, called photo symbionts, may have first appeared then. Tabulate corals formed large structures on the seafloor. Later, in the Devonian Period, warmer water may have caused problems for these corals.

Main article: Barrier reef
Main articles: Tabulate corals, Bioherms

Ireviken event

The Ireviken event was an early extinction event during the Silurian Period, happening around the time of the Llandovery and Wenlock boundary. It was first studied at places such as Ireviken and Gotland.

This event lasted about 200,000 years and affected many sea creatures, especially those in deeper waters. Shallow-water reefs were mostly safe. But many types of graptolites, conodonts, and trilobites disappeared. Scientists found changes in chemical signs in rocks from this time, showing shifts in the world's oceans.