Dinosaur Asteroid Hit the ‘Worst Possible Place’

GEOGRAPHY

Had the asteroid struck a different location, the outcome might have been very different. (BBC)

Zoom in on the Chicxulub impact crater, ground zero for the demise of the dinosaurs.

This impact was actually the least of the dinosaurs’ worries.
Illustration by Franco Tempesta, National Geographic

Discussion Ideas

  • How did an asteroid, comet, or other space rock lead to the demise of the dinosaurs?
    • The impactor didn’t directly cause any extinctions. Instead, it induced a “global winter” (sometimes called an “impact winter”).
      • The global winter was created by the injection of tons of sulfur into Earth’s atmosphere. The sulfur was emitted as tons of gypsum (a common sulfate mineral) evaporated upon the asteroid’s impact. As sulfur enters the stratosphere, it forms sulfuric acid. Sulfuric acid aerosols cooled Earth’s surface by reflecting solar radiation and inhibiting atmospheric circulation. (This process, called stratospheric aerosol injection, is a candidate for climate engineering to mitigate the current trend of global warming.)
      • The global winter led to the demise of about 75% of all life on Earth, including all non-avian dinosaurs. This phenomenon, called the Cretaceous-Paleogene extinction event, began almost immediately. “All these fossils occur in a layer no more than 10 centimeters (4 inches) thick,” says one paleontologist. “They died suddenly and were buried quickly … [T]his is a moment in geological time. That’s days, weeks, maybe months. But this is not thousands of years; it’s not hundreds of thousands of years. This is essentially an instantaneous event.”

 

This lovely illustrated image of Mexico’s Yucatan Peninsula shows a subtle indication of the Chicxulub impact crater in the upper left. Most scientists now agree that this impact was the cause of the Cretaceous-Paleogene extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs, as well as the majority of all life on Earth.
Image courtesy SRTM Team NASA/JPL/NIMA

  • Where on Earth did the space rock hit?
    • The overwintering asteroid crashed into the Gulf of Mexico, just off the northwest corner of the Yucatan Peninsula in what is today Mexico. The impact crater is known as the Chicxulub crater. The Chicxulub impactor is estimated to have been about 15 kilometers (9.3 miles) wide, and left a crater about 180 kilometers (110 miles) in diameter and 20 kilometers (12 miles) deep.

 

 

  • Did anything survive the Cretaceous-Paleogene extinction event? The shallow seas of Chicxulub may have been the worst place for an impact for the dinosaurs, but was it one of the best places any other animals?
    • Yes! In particular, the Cretaceous-Paleogene extinction event allowed mammals and plants to (slowly) undergo remarkable evolutions and adaptations during the Paleogene. This was a triumph of the little guy, bottom dwellers, and non-picky eaters.
      • little guys: Few tetrapods weighing more than about 25 kilograms (55 pounds) seem to have survived. The largest reptiles to survive included crocodilians and turtles. Birds survived, as did all major mammal lineages (if not specific species).
      • bottom dwellers: Deep-sea organisms were better able to survive the Cretaceous-Paleogene extinction event, as they rely less on phytoplankton than those in the epipelagic, or sunlight zone.
      • non-picky eaters: Terrestrial plant life was radically disrupted, which had the most staggering impact on life (and death) across the planet. Lacking nutrient-rich autotrophs as a food source, strict herbivores went extinct. So did strict carnivores. Omnivores, insectivores, and scavengers were better able to survive the event, likely due to an increase in their food sources.

 

TEACHERS TOOLKIT

BBC: Dinosaur asteroid hit ‘worst possible place’

Nat Geo: Chicxulub Impact Crater illustration

Nat Geo: What is a crater? reference

Wikipedia: Cretaceous–Paleogene extinction event (featured article)

Wikipedia: Chicxulub crater (featured article)

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s