The Ordovician: The Era of Corals, Trilobites, and Graptolites

The Ordovician lasted about 42 million years

The Ordovician is the second geological period of the Paleozoic Era, spanning from ~485 to ~443 million years ago. This period follows the Cambrian and precedes the Silurian. It is a key time marked by a major diversification of marine life and significant tectonic and climatic changes.

Climate and Environment

During the Ordovician, Earth initially experienced a globally warm climate, with high atmospheric CO\(_2\) levels favoring a high, shallow sea that covered much of the continents. Towards the end of the period, a gradual cooling set in, leading to the first major known glaciation, particularly on the continent of Gondwana, then located at the South Pole.

Biodiversity and Evolution

Marine life exploded in diversity during the Ordovician, a phenomenon often called the "Ordovician radiation". Trilobites, brachiopods, graptolites, and the first reef corals multiplied. The first primitive forms of fish also appeared. This biological dynamism was accompanied by a complexification of marine food chains.

Major Events

The Ordovician ended with a major mass extinction, affecting nearly 85% of marine species, linked to intense climatic cooling and glaciation. This extinction profoundly altered the composition of marine ecosystems and paved the way for evolution in the Silurian.