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November’s Science on Tap Question

How likely is it that an asteroid similar to the one that created the Chicxulub crater will crash into Earth, causing another extinction event like the one that killed the dinosaurs?
November 1, 2019
November’s Science on Tap Question

Photo credit Thomas Breher l Pixabay.

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The short answer is not very, for a couple reasons. The long answer is that the asteroid’s initial impact isn’t believed to have killed off most life on Earth 65 million years ago. There are currently two competing theories about what actually led to the world-wide extinction of over 75% of life on Earth.

One theory is that while many species located in the Chicxulub crater would certainly have perished instantly from the impact and blast force, that doesn’t really explain the global scope of the extinctions. Many of today’s scientists believe the mass extinctions were more likely caused by the ensuing climate change created by the enormous amounts of debris released into the air when the asteroid hit. Once released into the atmosphere, this layer of ash, dust, and other debris would have effectively blocked much of the sun’s radiation from reaching the earth’s surface and resulted in plummeting temperatures.  Also known as an “impact winter,” the drastic change in environment would have been too much, in too short a time, for the vast majority of plant and animal life to adapt and save their species.

An alternative theory is that debris (ejecta) from the impact was thrown into the upper reaches of the atmosphere and into low orbit.  Scientists surmise that then, within 24 hours, most of that super-heated material fell back to Earth within 24 hours.  These millions of airborne, incandescent heaters in the sky would have cooked the surface of the earth to hundreds, possibly even thousands of degrees F.  In this scenario, any life on the surface was most certainly dead within 24 hours of the asteroid’s impact. Scientists supporting this theory also believe climate change would have followed, leading to additional extinctions.

So, let’s go back to the short answer. There are a few, very simple reasons that most scientists agree that Earth’s risk of another catastrophic asteroid impact is pretty low:

  • While minivan-size or smaller asteroids do collide with Earth about thirty times a year, most of them burn up rather spectacularly in the atmosphere don’t even reach the ground.
  • Larger asteroids, those over 30 meters in size, are capable of devastating a city-size area, but occur only about once every two centuries.
  • Then there are the really big ones, the ones seen in Hollywood movies that could mean the end of life as we know it. Fortunately, the odds of one of these hitting is exceptionally low (1 in 50,000 chance in every 100 years).
  • And finally, there are many heavily invested organizations, including NASA and the Lab, with programs dedicated to detecting Near Earth Objects (NEO)–asteroids or comets passing within 30 million miles of Earth–and formulating plans to mitigate the risk these NEOs pose to Earth. In fact, According to NASA’s NEO program, no known asteroid larger than 140 meters in size has a significant chance to hit Earth in the next 100 years.

More information on the Lab’s research into asteroid risk mitigation can be found here.