Carnian pluvial episode

The Carnian pluvial episode (CPE), often called the Carnian pluvial event, was a time when Earth's climate changed a lot. This happened during the latter part of the Carnian Stage, the first part of the Late Triassic Epoch, about 234–232 million years ago. Volcanic activity near what is now North America caused global warming and more rain on land. It also changed the oceans by reducing carbonate platforms. Pluvial means "related to rain" or "characterized by rain."

The CPE was an important time for life on Earth. Many groups of animals that are important today began to grow and change during this event. The earliest dinosaurs (which include the ancestors of birds), lepidosaurs (the ancestors of modern-day lizards, snakes, and the tuatara), and possibly mammaliaforms (ancestors of mammals) all appeared and diversified. In the oceans, tiny plants called coccoliths and dinoflagellates first showed up. These helped corals grow better by living inside them as symbiotic partners.

We can see evidence of the CPE in rocks from the Carnian all over the world, both on land and under the sea. On land, the dry climate of the supercontinent Pangea became hotter and wetter, with much more rain. In the oceans, less limestone was made, leaving layers of mud as clues. These changes in the rocks show us how the climate changed during the Carnian pluvial event. This change was likely caused by large volcanic eruptions of flood basalts and volcanic CO2 near North America.

History and nomenclature

Scientists noticed big changes in Earth’s rocks from the Carnian time long before they thought about climate changes. They saw a dark layer in the Northern Limestone Alps that broke a long time of calm, sunny rock layers. They called this change the Reingrabener Wende.

In 1989, two scientists, Michael J. Simms and Alastair H. Ruffell, put many clues together and suggested that a time of lots of rain happened in the middle of the Carnian. They called this the Carnian pluvial episode. Their idea slowly gained support, especially after studies in Italy in the late 2000s. Today, scientists still discuss what caused this rainy time and how it changed life on Earth.

Environmental disruption

The Carnian pluvial episode brought more rain to the world, changing the dry weather of the Late Triassic period. We know this from clues like special soil and rocks that form in wet places, and fossil pollen that shows plants lived in humid areas.

The Earth also got warmer, probably because of big volcanic eruptions far off the coast of what is now North America. This warmth changed the oceans and how rocks formed. The wetter weather and warmer temperatures caused more rain and rivers to carry dirt and sand into the seas. This changed how limestone formed and affected many sea creatures.

Effect on life

Many sea creatures like conodonts, ammonoids, crinoids, bryozoa and green algae died out during this time. But other creatures, such as dinosaurs, calcareous nannofossils, corals and conifers, grew and spread.

The climate changes also affected land animals a lot. Some older reptiles, like rhynchosaurs, disappeared. Others, like hyperodapedontines, became common for a short time. New groups, including early aetosaurs and sauropodomorph dinosaurs, began to spread. Scientists discuss whether these changes were caused by the climate event or happened over longer periods.

Plants changed a lot too. Conifers, ferns and other plants became more common. Wet areas like swamps returned, helping more plants to grow. This plant growth may have helped balance the air around them. The first large deposits of tree resin, called amber, appeared during this time. They preserved tiny animals and plants very well.

Possible causes and influences

The Carnian Pluvial Episode happened because of a big area of volcanic rocks called the Wrangellia Large Igneous Province. The volcanoes released gases into the air. This made the Earth warmer and caused more rain. These changes affected both the oceans and the land.

Scientists studied rocks to learn about this time. They found changes in the carbon in the rocks. This showed that lots of new carbon entered the air and oceans. They also found small amounts of mercury, a metal that comes from volcanoes. These clues tell us that the big volcanoes helped change the Earth's climate.