Jun 19, 2017

Massive Volcanic Eruptions Triggered the Dinosaur Age

An artists depiction of a dinosaur and other animals escaping from an erupting volcano 235 million years ago in northwestern Argentina. Around 35 million years earlier, researchers believe that volcanic eruptions triggered the dawn of dinosaurs.
Intense volcanic eruptions, along with a devastating meteor strike, likely contributed to the extinction of non-avian dinosaurs around 66.5 million years ago. Now new research shows that volcanic eruptions at the end of the Triassic period (252–201 million years ago) triggered the Dinosaur Age, meaning these animals were bookended by some of Earth’s most extreme and fiery conditions.

The new evidence for volcanism, reported in the journal Proceedings of the National Academy of Sciences, corroborates earlier studies suggesting multiple volcanic eruptions occurred over a long period approximately 200–201 million years ago.

“The total duration of the end-Triassic volcanism is at least 700,000 years, and our paper supports the hypothesis that volcanic activity occurred on-and-off over that time, rather than being continuous for 700,000 years,” lead author Lawrence Percival of the University of Oxford said.

“How long the individual mega eruptions lasted isn’t something we can really answer at this time, but it is likely, based on other studies, that they would have lasted years–decades, with groups of such mega eruptions lasting hundreds–thousands of years,” he added.

Percival, along with colleagues Micha Ruhl, Stephen Hesselbo, Hugh Jenkyns, Tamsin Mather, and Jessica Whiteside, analyzed volcanic rocks and sediments dating to the latter part of the Triassic. The materials were sourced from the UK, Austria, Argentina, Greenland, Canada, and Morocco.

The field site in Morocco, where evidence for end-Triassic volcanism was found.
While studying these rocks and sediments, which once covered a huge area spanning four continents, the scientists focused on mercury content. They explained that volcanoes give off mercury gas emissions, which accumulates in sediments.

Their investigation found that nearly all of the sediment deposits showed large increases in mercury content beginning at the end-Triassic point in history.

“The mercury concentrations are shown to be in sediments of the same age as hugely extensive lava flows, further strengthening the case for volcanism being the source of this mercury,” Percival said.

He continued that the mercury increase was found to occur in the same sediments that record increased carbon dioxide during the end of the Triassic, supporting a volcanic origin for both gases.

This period further coincides with the end-Triassic mass extinction, which was once of the largest extinctions of animal life on record. Its long casualty list, including large crocodile-like reptiles and several marine invertebrates, amounted to around 76 percent of all terrestrial and marine species. The mass extinction also caused tremendous changes to land vegetation.

On the upside, it was during this time of death and destruction that dinosaur evolution really took off. Dinosaurs, which first emerged around 230 million years ago, were able to fill ecological niches left behind by the animals that went extinct. Some early mammals and amphibians benefitted from the food chain vacancies, too.  

As for how volcanism impacted the end-Triassic environment, Percival said, “The favored model is typically a short, sharp period of intense global cooling due to the initial release of sulphur aerosols and ash into the atmosphere, partly blocking sunlight, followed by more prolonged global warming caused by long-term volcanic carbon dioxide release.”

If Triassic animals like the giant croc-resembling reptiles were not directly burned to a crisp, they would have then experienced horrific climatic conditions challenging, and then ultimately ending, their existence.

Now two big questions remain. The first is: If the non-avian dinosaurs survived the end-Triassic volcanism, why did volcanic activity at the end-Cretaceous help to wipe them out? The researchers are not sure, but believe that the meteor impact 65.5 million years ago was a game changer, and that ecological factors were different during each extinction episode.

An artist’s recreation of the extinction of dinosaurs in the Deccan Traps of Western Ghats, India.
The second question is: If widespread volcanic activity coincided with two of the worst mass extinctions on Earth, could such massive eruptions happen again?

The researchers said that most of the huge volcanic events that took place over the past 200 million years on our planet were linked to the breakup of the supercontinent Pangea. Throughout the Dinosaur Age, Pangea continued to split into the continents seen today, and almost every split shows evidence for tremendous volcanism. Africa and South America, for example, retain evidence of similar lava flows of the same age preserved on their Atlantic coasts.

Read more at Discovery News

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