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Dawn of the Dinosaurs Triggered by Newly Discovered Mass Extinction Event



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A life scene from 232 million years ago, during the Carnian Pluvial episode, after which dinosaurs took over. A large Rauisuchian lurks in the background, and two species of dinosaurs stand in the foreground. Photo credit: Davide Bonadonna

Huge volcanic eruptions 233 million years ago pumped carbon dioxide, methane and water vapor into the atmosphere. This series of violent explosions on what is now Canada’s west coast led to massive global warming. Our new research has shown that this was a planetary-changing mass extinction that killed many of the dominants Tetrapods and heralded the beginning of the dinosaurs.

The most famous mass extinction occurred at the end of the chalk Period 66 million years ago. At this point, dinosaurs, pterosaurs, marine reptiles and ammonites died out. This event was mainly caused by the impact of a giant asteroid that obscured the sun’s light and caused darkness and freezing, followed by other massive disruptions to the oceans and atmosphere.

Geologists and paleontologists agree on a list of five such events, the last of which was the Cretaceous mass extinction. Our new discovery of a previously unknown mass extinction may therefore seem unexpected. And yet this event, known as the Carnian Pluvial Episode (CPE), appears to have killed as many species as the giant asteroid. Land and sea ecosystems have changed fundamentally as the planet got warmer and drier.

volcano

Huge volcanic eruptions changed life on earth 233 million years ago.

On land, this triggered profound changes in plants and herbivores. With the demise of the dominant herbivorous tetrapods like rhynchosaurs and dicynodonts, the dinosaurs got their chance.

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The dinosaurs originated about 15 million years earlier, and our new study shows that as a result of CPE, they expanded rapidly over the next 10 to 15 million years and became the dominant species in terrestrial ecosystems. The CPE started the “Age of the Dinosaurs” which lasted another 165 million years.

It wasn’t just the dinosaurs that took hold. Many modern groups of tetrapods such as turtles, lizards, crocodiles and mammals date from this newly discovered time of the revolution.

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This event was first perceived independently in the 1980s. However, it was believed to be restricted to Europe. First, about 232 million years ago, geologists in Germany, Switzerland, and Italy saw a large amount of marine faun sales known as the Rheingraben event.

In 1986 I independently recognized this as a worldwide sales between tetrapods and ammonites. But at that time age dating was much weaker than it is now and it was impossible to be certain that both were the same event.

The puzzle pieces started to fit when geologists Mike Simms and Alastair Ruffell spotted an episode of roughly 1 million years of humid climates across the UK and parts of Europe. Then the geologist Jacopo dal Corso discovered a temporal coincidence of the CPE with the height of the eruptions of the Wrangellia basalts.

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Wrangellia is a term geologists give to a narrow tectonic plate attached to the west coast of the North American continent north of Vancouver and Seattle.

Wrangellia Flood Basalts Card

Map showing the distribution of the Wrangellia flood basalts in Alaska, Yukon, and British Columbia. Photo credit: University of British Columbia (EOAS)

Finally off in a review of the evidence TriadThe signature of the CPE was found in aged rocks – not only in Europe, but also in South America, North America, Australia and Asia. This was anything but a Europe-only event. It was global.

volcanic eruptions

The massive Wrangellia eruptions pumped carbon dioxide, methane, and water vapor into the atmosphere, causing global warming and an increase in rainfall around the world. There were up to five eruption pulses associated with warming peaks from 233 million years ago. The eruptions led to acid Rain as the volcanic gases mix with rainwater to plunge the earth in dilute acid. Shallow oceans have also been acidified.

The strong warming drove plants and animals out of the tropics and the acid rain killed plants on land, while the acidification of the ocean attacked all marine organisms with carbonate skeletons. This removed the surfaces of the oceans and land. Life may have started to recover, but when the eruptions stopped, temperatures stayed high while tropical rainfall stopped. This led to the subsequent drying up of the land on which the dinosaurs flourished.

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Most unusual was the pouring over of the ship’s carbonate factory. This is the global mechanism by which calcium carbonate forms great limestone thicknesses and provides material for organisms such as corals and molluscs to build their shells. The CPE marked the beginning of modern coral reefs, as well as many modern groups of plankton, suggesting profound changes in ocean chemistry.

Major extinction events

Summary of major extinction events over time, highlighting the new Carnian Pluvial episode 233 million years ago. Photo credit: D. Bonadonna / MUSE, Trento

Before the CPE, the main source of carbonate in the oceans came from microbial ecosystems such as limestone-dominated mud hills on continental shelves. But after the CPE, it was powered by coral reefs and plankton, where new groups of microorganisms such as dinoflagellates emerged and flourished. This profound change in the fundamental chemical cycles in the oceans marked the beginning of modern marine ecosystems.

And there will be important lessons on how we can help our planet recover from climate change. Geologists need to study the details of Wrangellia’s volcanic activity and understand how these repeated eruptions drove the climate and changed the earth’s ecosystems. There have been a number of volcanic-induced mass extinctions in the history of the earth, and the physical disruptions such as global warming, acid rain, and ocean acidification are among the challenges we see today.

Paleontologists need to work more closely with data from marine and continental fossil records. This will help us understand how the crisis has impacted biodiversity loss, but it will also help us understand how the planet has recovered.

Written by Michael J. Benton, Professor of Vertebrate Paleontology, Bristol University.

Originally published on The Conversation.The conversation

For more information on this research, see Discovery of a New Mass Extinction – Carnian Pluvial Episode – 233 million years ago.

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