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Dino-killing asteroid could have thrust Earth into 2 years of darkness

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https://phys.org/news/2017-08-dino-killing-asteroid-earth-years-darkness.html

 

Tremendous amounts of soot, lofted into the air from global wildfires following a massive asteroid strike 66 million years ago, would have plunged Earth into darkness for nearly two years, new research finds. This would have shut down photosynthesis, drastically cooled the planet, and contributed to the mass extinction that marked the end of the age of dinosaurs.

extract:

Scientists also calculate that the force of the impact would have launched vaporized rock high above Earth's surface, where it would have condensed into small particles known as spherules. As the spherules fell back to Earth, they would have been heated by friction to temperatures high enough to spark global fires and broil Earth's surface. A thin layer of spherules can be found worldwide in the geologic record.


Read more at: https://phys.org/news/2017-08-dino-killing-asteroid-earth-years-darkness.html#jCp

 

the paper:

http://www.pnas.org/content/early/2017/08/15/1708980114

On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections:

Significance

A mass extinction occurred at the Cretaceous−Paleogene boundary coincident with the impact of a 10-km asteroid in the Yucatán peninsula. A worldwide layer of soot found at the boundary is consistent with global fires. Using a modern climate model, we explore the effects of this soot and find that it causes near-total darkness that shuts down photosynthesis, produces severe cooling at the surface and in the oceans, and leads to moistening and warming of the stratosphere that drives extreme ozone destruction. These conditions last for several years, would have caused a collapse of the global food chain, and would have contributed to the extinction of species that survived the immediate effects of the asteroid impact.

Abstract

Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous−Paleogene boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wildfires ignited after the impact of a 10-km-diameter asteroid on the Yucatán Peninsula 66 million y ago. Following injection into the atmosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injection of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth’s surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photosynthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.

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Probably a well known occurrence, so why did I post it? I believe it shows the power of science, the scientific method, and logical reasoning.

Edited by beecee

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As a former biomedical scientist, forgive me for being a bit sceptical but, it goes with the territory.  The modelling activity was very interesting however...

Quote

 

While the scientists think the new study gives a robust picture of how large injections of soot into the atmosphere can affect the climate, they also caution that the study has limitations.

For example, the simulations were run in a model of modern-day Earth, not a model representing what Earth looked like during the Cretaceous Period, when the continents were in slightly different locations. The atmosphere 66 million years ago also contained somewhat different concentrations of gases, including higher levels of carbon dioxide.

Additionally, the simulations did not try to account for volcanic eruptions or sulfur released from the Earth's crust at the site of the asteroid impact, which would have resulted in an increase in light-reflecting sulfate aerosols in the atmosphere.

The study also challenged the limits of the computer model's atmospheric component, known as the Whole Atmosphere Community Climate Model (WACCM).

"An asteroid collision is a very large perturbation—not something you would normally see when modeling future climate scenarios," Bardeen said. "So the model was not designed to handle this and, as we went along, we had to adjust the model so it could handle some of the event's impacts, such as warming of the stratosphere by over 200 degrees Celsius."

 



Read more at: https://phys.org/news/2017-08-dino-killing-asteroid-earth-years-darkness.html#jCp

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Surely the strength of this kind of research is that it throws up unexpected results, or uses simplifications, that inspire the next team of researchers to dig more deeply. Eventually we arrive at a satisfactory concensus.

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I suppose the only 'recent' event that blacked out the whole world would have been the Krakatoa explosion in 18 hundred and something? We were taught at school (although I have been caught out before parroting something I heard from school only to find it is untrue) that the explosion was heard about 7 times as the shockwave echoed round the earths atmosphere and that the ash particulates blocked out the sun worldwide for a few days.  

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