Rhaetian

The Rhaetian was the last age of the Triassic Period. It came after the Norian and was followed by the Hettangian, the first age of the Jurassic. Scientists use special methods to decide when the Rhaetian began and ended. They agree it ended about 201.4 million years ago.

In 2010, scientists tried to find the start of the Rhaetian by looking for a tiny sea creature called Misikella posthernsteini. There is still debate about when this happened. Studies from places like the Newark basin in the eastern United States and Turkey have offered different ideas. In 2024, the start of the Rhaetian was updated to about 205.7 million years ago.

During the Rhaetian, big changes were happening to the Earth's continents. The supercontinent Pangaea was starting to break apart, although the Atlantic Ocean had not yet formed. This was a time of important changes in Earth's history.

Stratigraphic definitions

The Rhaetian is named after the Rhaetian Alps, a mountain chain in Switzerland, Italy, and Austria. It was first described by scientists in 1856.

The start of the Rhaetian is marked by certain fossils, like a type of tiny tooth-shaped creature called Misikella posthernsteini. These fossils help scientists know when this time period begins. The end of the Rhaetian is marked by the appearance of a specific type of ammonite called Psiloceras.

Duration

The Rhaetian is the last part of the Triassic Period. It comes after the Norian and before the Hettangian, the first part of the Jurassic.

Scientists study rock layers to learn when the Rhaetian began. Some think it was short, about 2 to 4.5 million years. They looked at rocks in Turkey and Sicily. Others think it was longer, from 5 to 10 million years. They studied rocks in Italy and Austria.

Recent studies suggest the Rhaetian began about 205.5 million years ago. They studied ash layers in Peru and British Columbia. The end of the Rhaetian, called the Rhaetian-Hettangian boundary, happened about 201.4 million years ago. This was found by studying ash layers and fossils in Peru.

Notable formations

Some important rock layers from the Rhaetian time include the Lower Elliot Formation in South Africa, the Exter Formation in Germany, the 'Grès infraliasiques' Formation near Saint-Nicolas-de-Port in France, and the Penarth Group in England and Wales, part of the UK. These rock layers help scientists learn about Earth during the Rhaetian age.