Chapter 16: IMAGES FOR LECTURES
The End of the Dinosaurs
There have been many bad theories to explain dinosaur extinctions. But the most recent work on the KT extinction has centered on two hypotheses that suggest a violent end to the Cretaceous: a large asteroid impact and a giant volcanic eruption.
An Asteroid or Cometary Impact?
Asteroids do hit Earth, and there are many more in close orbits See this page for A Few Web Sites on asteroids
A sane look at asteroid dangers, from Clark Chapman. Chapman, C. R. 2004. The hazard of near-Earth asteroid impacts on earth. Earth and Planetary Science Letters 222: 1-15. Available on the Web
The last great impact on Earth: the probable cometary impact at Tunguska in 1908. From Discover magazine.
Craters
Chicxulub Crater
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Geophysical image of Chicxulub Crater
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Confirmation that there was one (and only one) asteroid strike at the K-T boundary. National Geographic News, November 30, 2006. Only a few scientists have been arguing for two or more strikes, but it's important to get it right.
How about this? Did an impact in India set off the K/T Deccan Traps eruption??? No, this is just more lousy science related to the K/T extinction. Why is this bad science? It calls for an impact even larger than Chicxulub, with the crater now conveniently covered by the Deccan Traps eruption that it allegedly started. Any theory that destroys the evidence by which you might test it is suspect, but why is there no mention of the global impact layer that this event must have caused. (People have looked up and down from the K/T boundary and have found NO (that's ZERO) sign of another impact, let alone a bigger one. Finally, there is no need for any impact to set off the Deccan Traps eruption: it's the breakthrough of a plume, the plume is still active (at Réunion Island), and the environmental insult of the Deccan Traps, coincident with the Chicxulub impact, already is larger than you need for the extinctions that occurred. But then, none of these folks understand paleontology or biology or ecology, and you can bet that the editors did not ask a paleontologist to review the paper(s) mentioned in this story. For more on Abbott and Isley's paper, see this press release from January 2003.
Tektites
Chaos in planets and the K-T extinction? Here we go again (June 28, 2001). IF you impute some chaos to planetary orbits (not unlikely), AND you program a series of computer models with built-in assumptions (as you must), they can simulate a history that has the inner planets changing orbits, BAM!, at 65 Ma. So you generate the K-T asteroid that way. Well, I suspect that it is a surprise to most planetary astronomers that we can post-dict such dramatic events at 65 Ma, and I know that you can get asteroid impacts without any such dramatic changes. So I think this is another loser: at best, it's unnecessary. I'd like to quibble a bit about Bruce Runnegar, too, as he portrays himself here. Bruce is a world-class expert on the paleontology of early molluscs: he is not an astrobiologist except that you get more NASA grant money as an astrobiologist than as a paleontologist. What is an astrobiologist, anyway, except a scientist who has nothing to study? (not an original remark). Well, that feels better. Now I'll give you the Web reference: BBC News OnLine
A Giant Volcanic Eruption?
Did a Catastrophe Cause the Extinctions?
Almost all the scientists directly involved in trying to explain the KT extinctions are emotionally committed to one catastrophic hypothesis or the other, or are emotionally against both. This has resulted in claims that seem to overinterpret the evidence available. One must be prepared to make one's own decision, and certainly all claims must be subject to close scrutiny.
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What Killed The Dinosaurs?
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Go to a special page for treatment of some extreme scenarios: they include the firestorm scenario, the microwave summer, the hypercane scenario, the EDS sex scenario, and possibly others as they appear.
The Ries Crater
A major impact formed the Ries crater in Germany at 15 Ma, throwing huge masses of boulders more than 100 km (60 miles) into Switzerland and the Czech Republic, and droplets of molten rock several hundred kilometers. The Ries impact did not affect even the local mammal fauna. A major impact at 51 Ma formed the Montagnais crater in the North Atlantic, 45 km (28 miles) across, and an impact hit Chesapeake Bay at 35 Ma, causing a crater 90 km (56 miles) across, but neither of them caused an extinction.
Geology of the K/T Boundary
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A fungal spike at the K-T boundary. Press release, March 8, 2004. The paper, by Vajda and McLoughlin, is in Science: open access but you have tio register (free). The fungal spike is in New Zealand. There's a huge fungal spike at the PT boundary, especially in Europe, and is attributed in that case to the decay of forests killed in the extinction event. One of the things that looks quite clear is that the KT forests were NOT burned up in a giant wildfire, otherwise there would have been nothing left to rot.
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Rainforest in North America only 1.4 m.y. after the K-T extinction. Science News. The paper was in Science: Johnson, K.R., and B. Ellis. 2002. A tropical rainforest in Colorado 1.4 million years after the Cretaceous-Tertiary boundary. Science 296:2379-2383.
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However, the post-K-T flora of North America was impoverished. It had only about 40% of the species found in the latest Cretaceous, and was composed almost entirely of the survivors of the extinction. Reference: Wilf, P., and K. R. Johnson. 2004. Land plant extinction at the end of the Cretaceous: a quantitative analysis of the North Dakota megafloral record. Paleobiology 30: 347-368.
Reference list for Chapter 16
Page last updated April 8, 2013.
Links checked March 16, 2013.
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