Climate

The Asteroid That Killed the Dinosaurs Caused Catastrophic Climate Change

Wildfires caused by the Chicxulub impact propelled soot high into the atmosphere, which blocked out the sun’s rays and cooled global temperatures by 50 degrees Fahrenheit.

Most schoolchildren learn the dinosaurs died out when an asteroid hit the earth.

Fortunately, schoolchildren are spared the gory details.

Scientists now believe that the asteroid that slammed into Mexico’s Yucatan Peninsula 66 million years ago was 6 miles wide — almost big enough to cover San Francisco — and caused cataclysmic destruction on a scale comparable to global thermonuclear war. In the aftermath, about three-quarters of all species on Earth died out.

The asteroid, named Chicxulub, sent huge tsunamis surging across the seas, and caused massive earthquakes and volcanoes. But that was just the beginning.

A massive amount of vaporized rock was propelled high above Earth, where it condensed into tiny particles and fell back down to the surface. Heated by friction, the descending cloud of rock dust reached temperatures hot enough to spark fires, literally broiling the Earth’s surface along with plant and animal life.

In other words, dinosaurs living far away from the Yucatan Peninsula were flambéed from above by the cloud of scorching rock particles falling on them. A thin layer of molten particles is still observable to geologists today.

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New research, however, now suggests that following the asteroid strike global temperatures plunged in a way analogous to the planetary cooling thought to follow a global nuclear war, commonly known as nuclear winter.

The resulting wildfires sparked by the broiling rock dust sent so much soot back up into the sky the sun was blackened out completely for most of the next two years, shutting down photosynthesis and dramatically cooling the planet in one of the most significant known episodes of climate change in Earth’s history.

Global temperatures plummeted by 50 degrees Fahrenheit on land and 20°F over the oceans.

On land, temperatures returned to normal in about seven years, though they were still a couple of degrees Celsius below normal 15 years later, according to Charles Bardeen of the National Center for Atmospheric Research, who led a study of Earth’s climate following the impact. The results were published in the journal Proceedings of the National Academy of Sciences.

Bardeen and his colleagues from NASA and the University of Colorado Boulder used advanced computer models to simulate the climate’s reaction during the years after the asteroid landed.

Rampant, sudden wildfires caused by the meteor impact cooled global temperatures in a way that is thought to be likely following widespread detonations of nuclear weapons, Bardeen said.

“Fires created by an asteroid impact and fires created by a nuclear war can put large amounts of soot high up above where the rain happens, so they can exist for a longer period of time and have these global consequences,” Bardeen said. “As long as that soot gets injected above where the rain would happen, it can stay in the atmosphere for a long time.”

Yet, perhaps surprisingly, the dinosaur-killing asteroid brought climate consequences that likely far exceeded those of a modern day limited nuclear war.

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A war between India and Pakistan, where perhaps 100 Hiroshima-sized nuclear weapons are used, would probably put enough soot into the atmosphere to have a 1-2°C impact on the atmosphere,” Bardeen said.

If the asteroid was so destructive, how did life on Earth survive at all?

Part of the answer lies in the shelter provided by the deepest oceans — places that don’t get much sunlight to begin with, and which were shielded from the fires.

“Oceans are a refuge,” Bardeen said. “Below about 500 meters, temperatures didn’t change much. Things in the deep ocean that might not need light either might have been able to survive feeding on debris that settled down there.”

Bardeen noted that on September 1 the 2.7-mile-wide asteroid Florence, named after Florence Nightingale, the founder of modern nursing, will pass about 4.4 million miles from Earth.

An event like the asteroid that killed the dinosaurs happens perhaps once every 200 million years, Bardeen said. “So it’s not something that we need to be worried about. Smaller ones are more frequent, though.”

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