Scientists Develop Clearer Idea of How Dino-Killing Asteroid Changed Earth's Environment

The last days of the dinosaurs occurred during the Cretaceous Period, when an object known as the Chicxulub impactor struck a shallow sea near what is now the Yucatan Peninsula. Stocktrek Images/Getty Images
The last days of the dinosaurs occurred during the Cretaceous Period, when an object known as the Chicxulub impactor struck a shallow sea near what is now the Yucatan Peninsula. Stocktrek Images/Getty Images

On this solar-powered planet, we get a little nervous about the things that take the light away: total solar eclipses have been causing mild to moderate trepidation in humans for millennia; our languages reflect distinct biases towards light and against dark ("ray of hope" vs. "darkest hour"); even regular old nighttime can be problematic for some of us.

Picture, then, what it must have been like for the dinosaurs just before they bought the proverbial farm. You're probably familiar with the basics of what happened 66 million years ago: a massive asteroid hit Earth — in Mexico's Yucatán Peninsula, which was at the time a shallow sea— and suddenly (relative to the long stretch of planetary history) there were no more dinos.

At least that's the sanitized version of the story. For some lucky organisms, death was quick, but others probably had to spend some time staggering around in a pitch-dark nightmare land.

It was probably terrible, but we don't know much about what the environmental aftermath of the asteroid's impact was actually like. And that lack of precise knowledge makes it tough to know much about why some species died and others survived. A new study published in the Proceedings of the National Academy of Sciences used advanced computer modeling techniques to figure out exactly what kind of wretched hellscape drove roughly three quarters of the planet's species — including all the nonavian dinosaurs and a disproportionately high number of marine species — to extinction.

"Our study picks up the story after the earthquakes and the tsunamis and the broiling."
Charles Bardeen, National Center for Atmospheric Research

The researchers found that the Chicxulub asteroid that ushered in the Cretaceous-Paleogene (K-Pg) extinction most likely triggered all sorts of cataclysmic natural disasters like earthquakes, tsunamis, and volcanic eruptions, in addition to wildfires ignited by the vaporized molten rock that rained down on every corner of the planet.

"The extinction of many of the large animals on land could have been caused by the immediate aftermath of the impact, but animals that lived in the oceans or those that could burrow underground or slip underwater temporarily could have survived," says lead author Charles Bardeen, a scientist at the National Center for Atmospheric Research, in a press release. "Our study picks up the story after the initial effects — after the earthquakes and the tsunamis and the broiling. We wanted to look at the long-term consequences of the amount of soot we think was created and what those consequences might have meant for the animals that were left."

It is not an insignificant amount of soot we're talking about here. The scientists estimate these worldwide wildfires that started after the asteroid hit launched around 15 billion tons (13.6 billion metric tons) of fine soot into the atmosphere, making daytime about as light as a moonlit night. Average temperatures on Earth's surface and at sea plummeted, with a 50 degree Fahrenheit (28 degree Celsius) drop over land, and a drop of 20 degree Fahrenheit (11 degree Celsius) over the oceans.

For more than a year and a half, photosynthesis would have been impossible for the terrestrial plants that weren't destroyed by the fires. And in the oceans, the phytoplankton would have been hit hard enough to tank the marine food chain. For a few months, our planet's energy source was removed, and a lot of animals starved.

Interestingly enough, the research team's models found that a fraction of soot in the atmosphere probably would have entirely shut down photosynthesis for a year: Actually, only 5 billion tons (4.5 billion metric tons) of soot would have done the trick. They also found that as Earth's seas, surface and lower atmosphere below the soot level cooled, all that soot absorbed the sun's light, heating and changing the chemistry of the upper atmosphere — destroying the ozone layer in the process. All the water in the atmosphere caused by the sudden warming eventually condensed into ice, creating a feedback loop that would very suddenly scoured all the soot out of the atmosphere over the course of just a few months.

The research team acknowledges the model isn't perfect. For instance, the simulations were run based on Earth as it is today and not during the Cretaceous Period, which means the continents were in different places and the concentration of atmospheric gases would have been slightly different. Also, the model didn't account for any sulfur released from volcanic eruptions resulting from the asteroid impact. However, the study provides a window into what existence would have been like for the final dinosaurs. And what the study revealed holds lessons for what our planet could be like if we involve ourselves in nuclear war:

"The amount of soot created by nuclear warfare would be much less than we saw during the K-Pg extinction," said Bardeen. "But the soot would still alter the climate in similar ways, cooling the surface and heating the upper atmosphere, with potentially devastating effects."