This Month in Science: What Happened to the Dinosaurs?

Despite the dreams of Hollywood, it’s unlikely that anyone will ever see a live Tyrannosaurus rex, Triceratops, Brachiosaurus, or any other ancient dinosaur. All of these dinosaur species are extinct—they no longer exist. Around 65.5 million years ago, all of the non-avian (unrelated to birds) dinosaurs died during what is called the Cretaceous-Paleogene (abbreviated K-Pg) extinction event1. You may also see it referred to as the Cretaceous-Tertiary, or K-T extinction. The Tertiary period was renamed the Paleogene period, but both terms are commonly used. This extinction event killed more than just the dinosaurs, eliminating 80 percent of the animal species alive at the time2.

While we know when the dinosaurs died, we don’t know exactly what killed them. There are several theories, but the prevailing one is the asteroid impact theory1. In 1980, Walter Alvarez, an experimental physicist, and his son Luis Alvarez, a geologist, published a paper stating that they discovered the iridium all over the world at the K-Pg boundary—a thin layer of rock that represents the boundary between the Cretaceous and Paleogene periods3. Iridium is a metal that is rarely found on Earth, but commonly found in asteroids. They suggested that the iridium deposits were a result of a massive asteroid crashing into Earth. The impact launched iridium debris into the sky that subsequently fell all over the planet4.

Initially met with skepticism, the theory gained more traction when the discovery of the Chicxulub crater, off the Yucatan peninsula in Mexico, was made public in the 1990s5. The crater was found in 1978 by geophysicists Glen Penfield and Antonio Camargo, who were working for an oil company. The discovery was kept a secret6, but after it was made public, researchers found that the Chicxulub crater strongly supported the asteroid impact theory5.

The crater is over 110 miles wide. Scientists estimate that the asteroid had to be about 6 miles across to create such a large crater. The asteroid impacted the Earth with the force of a 100 million megaton blast7. The collision caused tsunamis and earthquakes, and it ejected sediment and vaporized rock into the atmosphere1. Some scientists suggested that when the debris rained back down to Earth, the heat it radiated could have started forest fires across the globe8.

The initial impact was fatal to creatures in the immediate area. The resulting tsunamis and earthquakes led to the demise of many other animals, but they would have affected only a portion of the globe9. Researchers theorize that the bulk of the extinction resulted from impact debris blanketing the Earth’s atmosphere and blocking out sunlight1. Without adequate sunlight, global temperatures dropped and vegetation withered, reducing the available food for many dinosaurs and other species. As the herbivores struggled to find food, their populations waned. This depleted the food source available for carnivores, and they too died out.

An alternate theory suggests that a series of volcanic eruptions that formed the Deccan Traps in India led to the mass extinction. The Deccan Traps are lava beds that cover 200,000 square miles. The eruptions that formed the Deccan Traps erupted for around one million years and spanned the time before and after the K-Pg extinction10. While the eruptions released greenhouse gases and likely contributed to climate change, the geologic data obtained from the K-Pg boundary is stronger for the impact hypothesis than for volcanic eruption.

It is also possible that the extinction was not the result of one catastrophic event, but the cumulative effect of multiple factors. Volcanic eruptions, multiple asteroid impacts, and climate change may have all worked in tandem to end the 180 million-year reign of the dinosaurs. Ongoing research at the crater site and at a recently discovered site in North Dakota will provide more clues about what happened 65.5 million years.

The North Dakota site, named Tanis, is part of the Hell Creek Formation. Research suggests that the site represents a snapshot in time, immediately after the impact. It is thought that the asteroid impact caused a massive inundation of water to sweep through the area, burying nearby life, and preserving it for millions of years11. There are also rumors of dinosaur fossils at the site, but this has yet to be confirmed.

Come to the Museum and check out our newest traveling exhibit, Dinosaur Discovery. Act like a paleontologist and explore both real and replica dinosaur fossils. The exhibit was developed by the Virginia Museum of Natural History. Cape Fear Museum is also hosting the North Carolina Fossil Fair on November 2, 2019. Talk to fossil enthusiasts while they share their passion and knowledge of paleontology with the public.

References:

  1. Shulte, Peter et al. 2010. The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary. Science.
  2. https://www.britannica.com/science/K-T-extinction
  3. W. Alvarez, W. Alvarez, F. Asaro, and H.V. Michel 1980. Extraterrestrial cause for the Cretaceous—Tertiary Extinction. Science 208: 1095-1108.
  4. https://www.sciencenewsforstudents.org/article/dinosaurs-extinction-asteroid-eruptions-doom
  5. https://www.space.com/19681-dinosaur-killing-asteroid-chicxulub-crater.html
  6. http://www.chicxulubcrater.org/
  7. https://www.lpi.usra.edu/science/kring/Chicxulub/regional-effects/
  8. Melosh, H. J., et al. 1990. Ignition of global wildfires at the Cretaceous/Tertiary boundary. Nature343: 251-254. Microwave summer
  9. https://www.nytimes.com/2019/03/29/science/dinosaurs-extinction-asteroid.html
  10. https://www.sciencemag.org/news/2019/02/did-volcanic-eruptions-help-kill-dinosaurs
  11. https://www.sciencenews.org/article/new-fossils-north-dakota-dinosaur-killing-asteroid-impact

Previous Columns

May 2019: Hurricane Season
April 2019: Quantum Levitation
March 2019: Venus Flytrap
February 2019: A Shifting Magnetic Field
January 2019: Giant Ground Sloth
December: Snowflakes
November: Citizen Science
October: Parker Solar Probe Voyaging to the Sun
August: Sea Turtle Season
July: Plastic Free July
June 2018: All About Alligators


Source: National Geographic

Map of Chicxulub Crater location.
Source: Google Maps/UT Jackson School of Geosciences

Illustration of Chicxulub crater soon after impact, 65.5 million years ago.
Source: Detlev van Ravenswaay/Science

The Deccan Traps in India.
Source: Mark Richards/UC Berkeley (photo); Paul Renne/Berkeley Geochronology Center (map)/ScienceNews
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