Previously unknown mass extinction & rapid diversification: Carnian Pluvial Episode

[rogue06]

A team of researchers have discovered evidence of a mass extinction event which took place in the Late Triassic during an event known as the Carnian Pluvial Episode (CPE) some 233 mya, triggering the age when dinosaurs dominated the world by clearing a path for them to thrive in.

At this time the continents had all bunched together to form Pangea, with a dry and hot climate which is not uncommon for supercontinents. The desert age peaked in the Carnian, between 237 to 227 mya, but this changed rather abruptly for a relatively short period of time and likely triggered by massive volcanic eruptions in the Wrangellia Terrane^[1] of western Canada that laid down a thick layer of basalt (volcanic rock) and unleashed vast amounts of greenhouse gases such as carbon dioxide.

The team leader, Jacopo Dal Corso of both the China University of Geosciences and School of Earth and Environments, University of Leeds, United Kingdom observed that, "The eruptions were so huge, they pumped vast amounts of greenhouse gases like carbon dioxide, and there were spikes of global warming."

The climate change prompted a sharp increase in rainfall, leading to a humid period that lasted for one million years. Drought-tolerant plants were replaced by ones adapted to more humid conditions, and dolomite formation reveal that the water table became much higher. What is termed "The Great Wet" can be observed in rocks in Nova Scotia, Colorado, Morocco, China, India and Papua New Guinea, and others as well. New rivers formed, extending deltas and depositing sediments into the sea which was changing.

While this long rainy period has been known since the 1980s when geologists uncovered it, the accompanying mass extinction wasn't. Relatively short in length compared to some of the others in Earth's history, the CPE nevertheless significantly impacted life on Earth.

The climate change caused massive loss of biodiversity on land and ocean as can be seen by the disappearance of 33% of marine genera (the taxological ranking above species) which, according to the study, is "bigger than the well-known early Jurassic and Cretaceous extinctions." Conodonts, ammonoids, bryozoa, and green algae were all severely affected the CPE.

This was also a time that witnessed the arrival of new plants, animals, and marine life -- a massive biological radiation or diversification event. The change fostered the development of new plant life and the proliferation of the modern conifer forests, forming ecosystems more like those we see today. It was also the period where numerous groups of animals (like turtles, crocodiles, lizards, and mammals) first appeared.

More than the terrestrial flora and fauna, marine life such as modern-style coral reefs, several modern groups of plankton, and significant ocean chemistry and carbonate cycle changes resulted from this event.

And the end of the CPE was marked by the return of arid conditions, but new groups had taken over after the extinction event, which prompted the formation of and transition toward more modern-like ecosystems. As Professor Dal Corso said, the newly discovered extinction event played a significant role in "helping to reset life on land and in the oceans, marking the origins of modern ecosystems."

As for dinosaurs, both the start of the CPE and its end benefitted them

As one of the researchers, Mike Benson a paleontologist at the University of Bristol, said "We now know that dinosaurs originated some 20 million years before this event, but they remained quite rare and unimportant until the Carnian Pluvial Episode hit. It was the sudden arid conditions after the humid episode that gave dinosaurs their chance."

As the study noted "Latest dating has confirmed a temporal link between the CPE and the Carnian dinosaur diversification event, which took place across Pangea right after the CPE."

Source: Triassic period ended with 'lost' mass extinction and a million-year rain storm, study claims

Did a "lost" extinction 230 million years ago empty the oceans and pave the way for dinosaurs?


Long ago, before the dawn of the age of dinosaurs, a heavy rain descended upon the supercontinent of Pangaea — and it kept raining for more than 1 million years.

This epic rainy spell — known now as the Carnian Pluvial Episode (CPE) — occurred roughly 233 million years ago and was a stark shift from the typically arid conditions of the late Triassic period. But stormy skies weren't the only change Earth was facing. According to a study published Sept. 16 in the journal Science Advances, new fossil evidence suggests that the CPE was in fact a major extinction event — driven by volcanic eruptions and climate change — that resulted in the deaths of one-third of all marine species, plus a significant number of terrestrial plants and animals.

This "lost" extinction event doesn't quite reach the death toll of the five major mass extinctions typically discussed by the scientific community (the Permian-Triassic extinction, which occurred just 20 million years earlier, may have wiped out 90% of living species, for example). However, the study authors argue, the CPE isn't just important for what was lost — but also for what was gained. Far from just a period of death, the CPE was a period of "turnover," the researchers wrote, effectively paving the way for the dominion of the dinosaurs and the evolution of many terrestrial animal groups that still roam the Earth today.

"A key feature of the CPE is that extinction was very rapidly followed by a big radiation [of new species]," lead study author Jacopo Dal Corso, a geology professor at the China University of Geosciences in Wuhan, told reporter Scott Norris of Eos.org. "A number of groups that have a central role in today's ecosystems appeared or diversified for the first time in the Carnian [an age within the Triassic that lasted from 237 to 227 million years ago]."

Those groups include modern coral reefs and plankton in the oceans, Dal Corso told Eos, as well as the appearance of land-based fauna such as frogs, lizards, crocodilians, turtles and a diverse new swath of dinosaurs (who would thrive on Earth for the next 150 million years). Conifer trees also made their first appearance during the Carnian, further planting the roots of many modern ecosystems and inviting the "dawn of the modern world," the authors wrote in their new paper.

So, what brought on the world-changing rain in the first place? It's hard to say for certain, but the study authors believe the answers may lie in a continent-spanning lava field known as the Wrangellia Province, which runs for thousands of miles across the western coast of modern-day Canada. This massive igneous province was laid down by violent volcanism during the Carnian, and overlaps (at least partially) with the CPE.

Prior studies estimate that those mighty eruptions released at least 5,000 gigatons of carbon into the atmosphere (that's hundreds of times more than annual global emissions today), likely kicking off the extreme climate change that followed. The world became significantly more humid, heavy rains became the norm, the oceans acidified and entire species died in droves, paving the way for strange new plants and animals to slowly take over.

That's the story that the researchers envision in their new study, anyway. However, they acknowledge, much more work is needed to understand the full scope of the CPE and its possible triggers. There may have been other volcanic events at play beyond Wrangellia, the team wrote, but pinpointing them will be a challenge, as vast amounts of volcanic basalts from the Triassic period have already subducted into the Earth. Our ever-changing planet is eating its own history, leaving stones and bones as the only clues.


Source

© Copyright Original Source

The entire paper, Extinction and dawn of the modern world in the Carnian (Late Triassic), can be read at the provided link, and here is the Abstract from it:

Abstract

The Carnian Pluvial Episode (Late Triassic) was a time of global environmental changes and possibly substantial coeval volcanism. The extent of the biological turnover in marine and terrestrial ecosystems is not well understood. Here, we present a meta-analysis of fossil data that suggests a substantial reduction in generic and species richness and the disappearance of 33% of marine genera. This crisis triggered major radiations. In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals. Although there is uncertainty on the precise age of some of the recorded biological changes, these observations indicate that the Carnian Pluvial Episode was linked to a major extinction event and might have been the trigger of the spectacular radiation of many key groups that dominate modern ecosystems.

1. stretches from Alaska through southwestern Yukon and along the Coast of British Columbia in Canada - named for the Wrangell Mountains