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Ancient Extinction Has Ominous Lessons for Today: Study

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Scientists have nailed down the cause of a planet-wide catastrophe that wiped out nearly all living species 200 million years ago and paved the way for the rise of the dinosaurs. The culprit was carbon dioxide, the same greenhouse gas that’s causing global warming today says a new report.

The new study, which was published Thursday in the journal Science, said that unlike the current spate of warming, the gases that triggered the so-called End-Triassic Extinction (ETE) event came from an enormous series of volcanic eruptions, not from the burning of fossil fuels.

A study in the journal Science said that unlike the current spate of warming, the gases that triggered the so-called End-Triassic Extinction (ETE) event came from an enormous series of volcanic eruptions.
Credit: flickr/Óli Jón

Nevertheless, the result — a rapid rise in global temperatures and a change in ocean chemistry making seawater more acidic — is in many ways similar to what’s happening today, said Terrence Blackburn of the Carnegie Institution of Washington, who along with several colleagues authored the report.

“There’s a lot to be learned about how climate, life and the oceans respond to CO2,” Blackburn said in an interview.

To put it simply, things didn’t go well for vast numbers of plants and animals. No one knows the details of how many species perished, but it’s almost certainly the case that organisms that had evolved to thrive in conditions that existed just prior to the ETE couldn’t cope with changes in temperature, weather patterns and ocean chemistry that came with the massive spike in CO2 — the same general kinds of changes climate scientists believe are underway once again.

Scientists had long suspected that a gigantic series of volcanic eruptions triggered by the breakup of the world’s single continent, Pangaea, was the cause of the ETE, but while the eruptions and the extinctions broadly coincided, the timing of the former wasn’t known with enough precision to qualify it as a smoking gun. Indeed, some geologists had argued that the eruptions actually came after the extinction.

To nail down the timing more precisely, Blackburn and his colleagues collected zircon crystals from some of the 2.5 million cubic miles of cooled lava spewed out of those ancient volcanoes — including samples from the Palisades, a line of cliffs that residents of Manhattan’s Upper West Side can easily see from across the Hudson River.

Scientists had long suspected that a gigantic series of volcanic eruptions triggered by the breakup of the world’s single continent, Pangaea.
Credit: flickr/Narisa

Inside those crystals, the scientists were able to find samples of uranium that had partly decayed into lead. The relative amounts of those two elements allowed them to calculate how long the decay process had been going on, and thus when the eruptions happened. There were four separate pulses of volcanism, it turns out, spread out over some 600,000 years. But one powerful pulse came at 201 million years before the present, which puts the eruption at more or less exactly the same time as the extinction event.

Precisely how much CO2 would have entered the atmosphere is unknown. “There’s still some debate,” Blackburn said. “Some say the atmospheric concentration doubled, some say it tripled.”

Whatever the amount, the devastating effects on life are clear from the fossil record. For the dinosaurs, of course, the End-Triassic Extinction was a blessing, giving them a clear evolutionary playing field on which to flourish. The world was all theirs for the next 135 million years or so, until an asteroid slammed into Earth about 65 million years ago, causing the fifth mass extinction in the planet’s history and giving mammals a chance to take over.

Today, thanks to greenhouse gases from the burning of fossil fuels; deforestation and other changes wrought by human activity, biologists believe a sixth great extinction is under way. This time, there isn’t a volcano or asteroid to blame.  

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Comments

By FishOutofWater (Jacksonville NC)
on March 21st, 2013

“samples of uranium that had partly decayed into lead”

Not exactly. Trace amounts of Uranium were incorporated in to the crystal structure of zircon.  Uranium is radioactive with a very well known decay rate. Geochemists measured the precise amount of decay of uranium to lead to determine the precise age of the zircon crystal.

Reply to this comment

By Addinall (Brisbane/QLD/4010)
on March 23rd, 2013

That is strange as the global “average” temperature was 25C throughout the WHOLE of the Triassic period.  The steep climb from 10C (Ice age) to
27C (no ice anywhere on Earth) started in the early Permian.  The end of the Permian saw CO2 levels at about 1800ppm and CO2 DECLINED throughout the Triassic halfway into the Jurassic.  Mid point during the Jurassic CO2 level increased remarkable quickly to around 3000ppm.  During this increease in CO2 saturation of the atmosphere, the global “average” temperature plummeted from 25C back into a semi-glacial state of about 16C.

Then during the Cretaceous, CO2 in the atmosphere steadily DECLINED to about 1700 ppm aqnd at the same time as this decline, the temperature INCREASED back up to 25C.

http://www.addinall.net/climate_history.gif
http://www.scotese.com/climate.htm

As you can see from these charts, Earth is still very much in an ice age, and the level of atmospheric CO2 is at a historically quite low level.

There was no “massive spike” in the level of CO2 during the Triassic.  THere was a steady DECLINE in atmospheric CO2.  The “massive spike” occured in the mid to late Jurassic, when the temperatures fell several degrees and causing the poles to freeze once again.

Reply to this comment

By Dave (Basking Ridge, NU 07920)
on March 24th, 2013

@Addinall

I was surprised by the highly categorical nature of your comment given that accepted paleoclimate data, especially for deep time such as that measured in 100’s Ma bp, is understandably, typically imprecise. In fact it looks to me like you are quoting an out of date GEOCARB model minus the huge uncertainty range that goes with it as if it is historical fact. A later GEOCARB model and also other relevant models as well as various discrete proxy measurement data for this broad period are pertinent. 

If confirmed, the direct connections between a sharp rise in CO2, global temperature and the fourth mass extinction event would indeed be an aggressive history lesson. 

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