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What if the Chicxulub meteor Had Missed the Earth?

A map of the Chicxulub crater
A map of the Chicxulub crater made from data gathered aboard the space shuttle in 2003. You can see the rim of the crater in the upper left. See more dinosaur pictures.

On the northern coast of the Yucatan Peninsula, near the town of Chicxulub, Mexico, is a crater about 120 miles (193 kilometers) in diameter. The asteroid that created this crater was about 6 miles (10 kilometers) wide and hit the Earth 65 million years ago. In spite of these immense measurements, the crater is hard to see, even if you're standing on its rim. To get a good map, NASA researchers examined it from space.

Ten years before the 1990 discovery of the Chicxulub crater, physicist Luis Alvarez and geologist Walter Alvarez, a father-son team, proposed a theory about the impact that created it. They noted increased concentrations of the element iridium in 65-million-year-old clay. Iridium is rare on Earth, but it's more common in some objects from space, like meteors and asteroids. According to the Alvarez theory, a massive asteroid had hit the Earth, blanketing the world in iridium. But a shower of particles wasn't the only effect of the collision -- the impact caused fires, climate change and widespread extinctions. At the same time, dinosaurs, which until then had managed to survive for 180 million years, died out. Geophysicist Doug Robertson of the University of Colorado at Boulder theorizes that the impact heated the Earth's atmosphere, causing most big dinosaurs to die within hours [source: Robertson].

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This mass extinction definitely happened. Fossil evidence shows that about 70 percent of species living on Earth at the time became extinct [source: NASA]. The massive die-off marks the border between the Cretaceous and Tertiary periods of the Earth's history, which are also known as the Age of Reptiles and the Age of Mammals, respectively. Today, scientists call the extinction the K-T event after the German spellings of "Cretaceous" and "Tertiary."

The K-T event had an enormous effect on life on Earth, but what would have happened if the asteroid had missed? Would it have led to a world where people and dinosaurs would coexist -- or one in which neither could live?

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If the meteor had missed, would kids play with toy dinosaurs or real ones?
If the meteor had missed, would kids play with toy dinosaurs or real ones?
Ronnie Kaufman/Larry Hirshowitz/Blend Images/Getty Images

In a world where an asteroid whizzed past Earth instead of crashing down with the force of 100 million tons of TNT, life could have progressed much differently. Sixty-five million years ago, some of the animals and plants that are common today were just getting started. These include placental mammals and angiosperms, or flowering plants. Insects that rely on flowers, such as bees, were also relatively new. Many of these life forms thrived after the K-T event, and without the mass extinction to clear the way, they may not have found ecological niches to fill. In this scenario, today's world might be full of reptiles and short on mammals -- including people.

But even if the asteroid hadn't hit, dinosaurs and other Cretaceous life forms might have become extinct anyway. Some dinosaur species had started to dwindle long before the asteroid's impact. This has led most researchers to conclude that the asteroid was just one aspect of a complex event. Other global catastrophes, like massive volcanic eruptions in what is now India, most likely played a role. Also, the Earth's changing landscape as the supercontinent Pangaea broke up into today's continents probably had something to do with it, too.

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Then there's another argument -- that the Chicxulub asteroid hit the Earth too early to have caused the extinction. Researchers Gerta Keller and Markus Harting both conclude that the impact took place 300,000 years before the end of the Cretaceous period. Keller, of Princeton University, theorizes that the Chicxulub impact was one of at least three massive collisions [source: Schultz]. Harting, of the University of Utrecht, argues that the iridium layer didn't come from the Chicxulub asteroid but from another event, such as a series of meteors burning up in the atmosphere. He bases this theory on spheroid particles ejected during the impact. Most of these are in an older layer of the Earth than the K-T iridium layer [source: Cairns]. According to both of these points of view, the absence of the Chicxulub asteroid strike may not have had a big effect on the K-T extinction.

It's hard to come to a definitive conclusion about what the world would look like today without the Chicxulub impact. But the question of whether people and dinosaurs could have coexisted is a captivating one. The idea is present in everything from the Congo legend of Mokele-Mbembe to "King Kong" and an episode of the BBC series "Horizon" called "My Pet Dinosaur." Then, of course, there's the prevailing scientific theory about the origin of birds -- that they are, in essence, living dinosaurs. You can read more about all the competing theories on the next page.

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Sources

  • Cairns, Ann. "More Evidence Chicxulub Was Too Early." Geological Society of America. Press release. 3/29/2006. (9/4/2008) http://www.geosociety.org/news/pr/06-14.htm
  • Kring, David A. "Chicxulub Impact Event." NASA/UA Space Imagery Center's Impact Cratering Series. (9/4/2008) http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html
  • NASA Jet Propulsion Lab. "K-T Event." (9/4/2008) http://www2.jpl.nasa.gov/sl9/back3.html
  • National Geographic News. "'Dinosaur-Killer' Crater Imaged for First Time." 3/7/2003. (9/4/2008) http://news.nationalgeographic.com/news/2003/03/0307_030307_impactcrater.html
  • Rincon, Paul. "Dinosaur Impact Theory Challenged." BBC News. 3/1/2004. (9/4/2008) http://news.bbc.co.uk/2/hi/science/nature/3520837.stm
  • Robertson, Doug. "Study: Dinosaurs Died Within Hours After Asteroid Hit Earth 65 Million Years Ago." University of Colorado at Boulder. Press release. 3/24/2004. (9/4/2008) http://www.colorado.edu/news/releases/2004/168.html
  • Schultz, Steven. "Dinosaur Dust-up." Princeton Weekly Bulletin. 9/22/2003. (9/4/2008) http://www.princeton.edu/pr/pwb/03/0922/
  • University of California Museum of Paleontology, Berkley. "Tour of Geologic Time." (9/4/2008) http://www.ucmp.berkeley.edu/exhibits/geologictime.php

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