Rhaetian

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

Scientists know the end of the Rhaetian well, but they still talk about when it began.

In 2010, scientists looked for a special tiny sea creature called Misikella posthernsteini to help decide when the Rhaetian began. But there is still debate about the exact time. An important place for studying this time is the Newark basin in the eastern United States.

New studies using radiometric dating of fossils from Peru suggest that the Rhaetian might have started around 205.7 million years ago. This is different from older ideas.

During the Rhaetian, the big landmass called Pangaea began to break apart, but the Atlantic Ocean had not yet formed.

Stratigraphic definitions

The Rhaetian is named after the Rhaetian Alps, a mountain chain in Switzerland, Italy, and Austria. Scientists first described this time period in 1856.

The start of the Rhaetian is marked by special fossils, like a tiny sea creature called Misikella posthernsteini. These fossils help scientists know when this time period begins. At the end of the Rhaetian, another special fossil called Psiloceras appears, marking the start of the next time period, the Hettangian.

Duration

The Rhaetian is the last part of the Triassic Period. It comes after the Norian and before the Hettangian, which is the first part of the Jurassic Period. Scientists study rocks around the world to learn when the Rhaetian began and ended.

Some scientists thought the Rhaetian was a short time, less than 5 million years. They studied rocks in places like Turkey and Sicily. Others thought it was longer, between 5 to 10 million years. They looked at rocks in Italy, Austria, and Japan.

Recent studies suggest the Rhaetian began about 205.5 million years ago. The end of the Rhaetian is about 201.4 million years ago. These dates help us understand the Rhaetian and its place in Earth's history.

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 layers help scientists learn about the Earth from long ago.