Llandovery Epoch

The Llandovery Epoch, also known as the Early Silurian, was a time period that began around 443.1 million years ago and ended about 432.9 million years ago. It was the first part of the Silurian Period in Earth's history. This epoch came right after the Ordovician-Silurian extinction events, which caused many plants and animals to disappear, changing the world’s ecosystems.

During the Llandovery Epoch, reefs began to form widely in the oceans. These reefs were built by ancient animals like corals, and they kept growing into the Devonian Period. However, when water temperatures rose too high, many corals died because their tiny plant friends, called symbionts, could no longer survive.

The Llandovery Epoch came to an end with an event known as the Ireviken event. This event caused many trilobites, which were sea creatures with hard shells, to vanish, and it also greatly reduced the number of conodonts, small fish-like animals. These changes helped shape life on Earth for millions of years to come.

Beginning of Silurian

The end of the Ordovician–Silurian extinction event happened when melting glaciers raised sea levels, which then stabilized. As the seas returned, life began to recover, and many animal groups bounced back.

After this big loss of species, communities in the Silurian were simpler at first. The animals that survived were found all over the world, unlike before. Even though these events didn’t change life as much as later extinctions did, many species still disappeared quickly, shaping the world’s biodiversity.

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 figure out when this important time in Earth’s history began.

Subdivisions

The Llandovery Epoch is divided into three main stages: Rhuddanian, Aeronian, and Telychian.

In some places, like North America and Estonia, people use different names for these stages. For example, in North America, the stages are called Ontarian and Alexandrian, while in Estonia, they are called Adavere, Raikküla, and Juuru.

Palaeontology

Spores and plant microfossils have been found in China and Pennsylvania. During the Llandovery Epoch, there was some movement of plants to land areas, but the earliest known vascular plants, like Cooksonia, appeared only in middle Silurian rocks.

One interesting fossil found from this time is Parioscorpio venator. It was first thought to be the earliest land animal, possibly a scorpion, but later studies suggested it was actually a marine arthropod.

Reef expansion

Barrier reef systems covered more of the ocean floor than they do today and grew even in places far from the equator. It’s possible that the tiny plants that live inside corals, called photo symbionts, first appeared during this time. Tabulate corals formed large, important 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, occurring around the time of the Llandovery and Wenlock boundary. It was first studied at locations such as Ireviken and Gotland.

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