Toarcian

The Toarcian is a time period in Earth's history, part of the Early or Lower Jurassic, which lasted from about 184.2 million years ago to 174.7 million years ago. It came after the Pliensbachian and was followed by the Aalenian. Scientists use the Toarcian to help understand how Earth and its living things changed long ago.

The beginning of the Toarcian Age was marked by a big change called the Toarcian Oceanic Anoxic Event. During this time, the oceans lost oxygen, which caused many sea creatures to die out and led to higher temperatures all over the world. This event made the fossils found from this time very different from those before it.

At the end of the Toarcian, Earth experienced a cooling period known as the Comptum Cooling Event. However, scientists are still discussing whether this cooling happened all around the world or just in some places.

Stratigraphic definitions

The Toarcian gets its name from the city of Thouars in the Loire Valley of France. This time period was first described in 1842 by a scientist named Alcide d'Orbigny after he studied rock strata near Thouars.

In Europe, the Toarcian is part of a layer of rocks called the Lias. Scientists mark the beginning of the Toarcian by looking for the first appearance of a special type of fossil shell called the ammonite genus Eodactylites. The end of the Toarcian is marked by the appearance of another ammonite genus called Leioceras.