Sulfur Clouds May Have Killed Dinosaurs : Science: Researchers at JPL and in Moscow theorize that the impact of a giant comet sent poisonous plumes into the atmosphere, causing deadly rains.
Scientists still mourning the demise of the dinosaurs 65 million years ago now suspect that the behemoths may have succumbed to the sulfurous atmosphere created when an immense asteroid smashed into a region of the Yucatan Peninsula uniquely rich in brimstone.
Researchers at the Jet Propulsion Laboratory in Pasadena and the Russian Academy of Sciences in Moscow say the release of sulfur fumes caused by the impact would have been enough to plunge the planet into a global winter lasting decades, shrouding it in sulfuric acid clouds like those veiling the planet Venus.
The discovery provides a key piece of evidence in support of the longstanding theory that an impact could have triggered a global catastrophe lasting long enough to cause mass extinctions. The location of the impact itself--in an area thick with sulfur-bearing rock--was crucial. Had the asteroid hit almost anywhere else, the scientists suggested, dinosaurs might still be with us.
“Sulfur does rather nasty things when it gets vaporized and shot up into the atmosphere,” said Kevin O. Pope, a private research consultant at Geo Eco Arc Research in La Canada, who led the international team of researchers. “That is why it was so lethal to the dinosaurs.”
The researchers base their idea on computerized climate models, crater geology and extensive fieldwork in a sulfur-rich region where an asteroid is believed to have struck Earth about the time dinosaurs became extinct. The work results from an unusual collaboration between U.S. experts in exotic planetary atmospheres and a Russian specialist in the dynamics of how impact craters are formed. They also analyzed car-sized boulders of impact debris quarried near the crater.
The new evidence, detailed in research published in Earth and Planetary Science Letters, a European journal, is the latest addition to a long-running scientific controversy over what killed off the creatures that ruled the planet unchallenged for much of Earth’s history.
There is no shortage of prime suspects. The idea that the dinosaurs were the victims of the impact of a doomsday comet or large asteroid--between 10,000 times and 50,000 times more powerful than the comet that collided with Jupiter this past summer--has been the subject of intense debate since 1980.
But others say the comet scenario is unlikely. Rather, they blame immense lava flows, planetary tidal waves, climate change, and even virulent plagues as the possible culprits in one of nature’s most provocative murder mysteries.
Until now, some researchers were concerned that the impact of a massive asteroid or comet could not by itself cause a long-lasting disruption encompassing enough of the planet to cause the extinction of thousands of species.
For instance, experts have long been tantalized by continent-sized volcanic flows in Earth’s past that appear to coincide with periods of mass extinction. Some scientists, taking a clue from impact basins and ancient volcanic activity on Mars, recently suggested that shock waves from an asteroid’s impact could have caused such catastrophic outpourings of molten rock. The Earth’s crust could focus shock waves from an impact, they say, to trigger huge volcanoes on the opposite side of the planet, called the antipode.
Several scientists have argued that a basalt formation called the Deccan Traps, a flood of lava that covered much of ancient India 65 million years ago, might have been triggered when an asteroid smashed into the Yucatan. At that time, because of continental drift, the two points would have been on opposite sides of the planet. The resulting firestorms, chemical fumes and widespread devastation might have contributed to the planetary disaster.
Dating experts at the Berkeley Geochronology Center, however, dispute the idea. Their research indicates that the lava plume “incubated” in the crust for about 3.5 million years before erupting onto the surface. That makes it less likely that the lava simply burst through the crust in response to the shock of the asteroid.
In the thick deposits of sulfur hydrite rock in the Yucatan, the JPL researchers found another explanation.
The vaporized sulfur released into the atmosphere would have doubled the length of the planetary blackout caused by dust and debris from the impact, causing total darkness for up to six months, said Kevin H. Baines, a JPL planetary scientist. The sulfur particles are significantly lighter than most dust particles and so would stay aloft longer. When they were finally washed out of the air, they would fall as highly acidic rain, deadly to vegetation.
More important is the effect the sulfur would have on the chemistry of the atmosphere, Baines and Pope said. A series of reactions would result in a severe global winter lasting anywhere from a decade to a century, cold enough to leave even the tropics near freezing.
The disaster would unfold in predictable stages. At first, the immense sulfur fumes spewing from the crater would combine with oxygen to form sulfur dioxide. Rising high into the atmosphere, the sulfur dioxide would react with ultraviolet light and water vapor to form sulfuric acid.
The resulting acidic clouds, like those on Venus, would be thick enough to cut the amount of sunlight reaching earth’s surface by about 20%, the researchers said. That is enough to drop temperatures worldwide by more than 20 degrees Fahrenheit.
“The unique aspect of this is the unusual site with the sulfuric element in the ground,” Baines said. “The asteroid not only caused the largest known impact on Earth, but the asteroid hit the one spot on Earth that would cause a worldwide cataclysm,” he said. “Only 5% of the earth has this kind of sulfur-bearing rock.”
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Killer Asteroid? Scientists suspect that dinosaurs may have succumbed to the sulfurous atmosphere created when an immense asteroid smashed into a unique region of the Yucatan Penninsula that is unusally rich in brimestone, leaving a crater 125 miles in diameter. The sulfer fumes released by the impact would have been enough to cause a global winter lasting decades.
