The end-Triassic extinction along with the end-Permian and end-Cretaceous events are the most severe mass extinctions in the past 270 million years. The exact mechanisms of the end-Triassic extinction have long been debated, but most prominent: carbon dioxide surfaced by volcanic eruptions built up over many millennia, raising temperatures to unsustainable levels for many creatures, and acidifying ocean waters. But a new paper in the Proceedings of the National Academy of Sciences says the opposite: cold, not warmth was the main culprit.
Outcrop area of CAMP rocks in Pangea showing paleolatitudes at CAMP time (201 million years ago) of key localities with the terrestrial end-Triassic extinction including the Newark Basin (NB) in northeastern North America, the Fundy Basin (FB) of Atlantic Canada, and the Central High Atlas (CHA) Basin of Morocco. Image credit: Kent et al., doi: 10.1073/pnas.2415486121.
The end-Triassic mass extinction occurred 201.564 million years ago and resulted in the demise of some 76% of all marine and land species.
This mass extinction coincided with massive volcanic eruptions that split apart the supercontinent Pangea.
Millions of km3 of lava erupted over some 600,000 years, separating what are now the Americas, Europe and North Africa.
The event marked the end of the Triassic period and the beginning of the Jurassic, the period when dinosaurs arose to take the place of Triassic creatures and dominate the planet.
The new study presents evidence that instead of stretching over hundreds of thousands of years, the first pulses of lava that ended the Triassic were stupendous events lasting less than a century each.
In this condensed time frame, sunlight-reflecting sulfate particles were spewed into the atmosphere, cooling the planet and freezing many of its inhabitants.
Gradually rising temperatures in an environment that was hot to begin with — atmospheric carbon dioxide in the Late Triassic was already three times today’s level — may have finished the job later on, but it was volcanic winters that did the most damage.
“Carbon dioxide and sulfates act not just in opposite ways, but opposite time frames,” said Dr. Dennis Kent, a researcher at Lamont-Doherty Earth Observatory.
“It takes a long time for carbon dioxide to build up and heat things, but the effect of sulfates is pretty much instant. It brings us into the realm of what humans can grasp. These events happened in the span of a lifetime.”
The Triassic-Jurassic extinction has long been thought tied to the eruption of the so-called Central Atlantic Magmatic Province (CAMP).
In their study, Dr. Kent and colleagues correlated data from CAMP deposits in the mountains of Morocco, along Nova Scotia’s Bay of Fundy, and New Jersey’s Newark Basin.
Their key evidence: the alignments of magnetic particles in the rocks that recorded the past drifting of Earth’s magnetic pole at the time of the eruptions.
Due to a complex set of processes, this pole is offset from the planet’s unchanging axis of rotation — true north — and to boot, changes position by a few tenths of a degree each year.
Because of this phenomenon, magnetic particles in lavas that were emplaced within a few decades of each other will all point in the same direction, while ones emplaced, say, thousands of years later will point 20 or 30 degrees in a different direction.
What the researchers found was five successive initial CAMP lava pulses spread over about 40,000 years — each with the magnetic particles aligned in a single direction, indicating the lava pulse had emerged in less than 100 years, before drift of the magnetic pole could manifest itself.
These huge eruptions released so many sulfates so quickly that the sun was largely blocked out, causing temperatures to plunge.
Unlike carbon dioxide, which hangs around for centuries, volcanic sulfate aerosols tend to rain out of the atmosphere within years, so resulting cold spells don’t last very long.
But due to the rapidity and size of the eruptions, these volcanic winters were devastating.
The scientists compared the CAMP series to sulfates from the 1783 eruption of Iceland’s Laki volcano, which caused widespread crop failures; just the initial CAMP pulses were hundreds of times greater.
In sediments just below the CAMP layers lie Triassic fossils: large terrestrial and semiaquatic relatives of crocodiles, strange tree lizards, giant, flat-headed amphibians, and many tropical plants. Then they disappear with the CAMP eruptions.
Small feathered dinosaurs had been around for tens of millions of years before this, and survived, eventually to thrive and get much larger, along with turtles, true lizards, and mammals, possibly because they were small and could survive in burrows.
“The magnitude of the environmental effects are related to how concentrated the events are,” said Dr. Paul Olsen, also from Lamont-Doherty Earth Observatory.
“Small events spread out over tens of thousands of years produce much less of an effect than the same total volume of volcanism concentrated in less than a century.”
“The overarching implication being that the CAMP lavas represent extraordinarily concentrated events.”
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Dennis V. Kent et al. 2024. Correlation of sub-centennial-scale pulses of initial Central Atlantic Magmatic Province lavas and the end-Triassic extinctions. PNAS 121 (46): e2415486121; doi: 10.1073/pnas.2415486121
Source : Breaking Science News