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Unformatted text preview: GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Cenozoic Overview Lecture Goals : A) The end of the Mesozoic (Die dinosaurs die!) B) Cenozoic time frame and key events C) Paleoceanography (Messinian Salinity Crisis) Textbook reference: Levin (2003) 7 th edition, Chapters 13 & 14; Levin (2006) 8 th edition, Chapters 15 & 16 A) The end of the Mesozoic There isn’t a human being alive today (well maybe a few in the jungles of Papua New Guinea) who isn’t aware that something really bad happened to mark the end of the Mesozoic era. Some refer to this disaster as the terminal Cretaceous event . Others simply state that “it’s when the dinosaurs bit the big one”. In reality, more than just the dinosaurs died off at this time. This, perhaps the 3 rd greatest mass extinction in Earth history, also saw the extinction of the ammonites and several other orders and families of animals. The event has been the subject of several (mostly bad) Hollywood blockbuster movies and is a constant reminder about just how precarious life is on a planet orbiting a sun in the vast and not entirely empty wastelands of space. So what happened 65 million years ago? What caused the terminal Cretaceous event? Why did the dinosaurs die off? These are questions that have bugged scientists for decades. The most widely accepted idea today is that a large asteroid/comet impacted the Earth leaving a crater 170 km wide near what is today Chicxulub on the Yucatan Peninsula of Mexico. The idea that an extraterrestrial impact might cause mass extinctions was not new. Anyone who looked at the full moon on a cloudless night could see huge impact craters and most would ponder the effects of similar events on the Earth’s ecosystems. But finding the location of impact sites on a planet mostly covered in water with active erosion and plate tectonics is not easy. There are plenty of craters on the Earth, but few if any can be linked to a specific mass extinction event. The Permian- Triassic extinction is suspected by many as being the result of a great impact, but no crater has (yet) been found to prove it. In 1980, two clever father and son geologists (Walter and Luis Alvarez ) published some geochemical analyses from sedimentary rocks that straddled the K-T boundary . They were particularly interested in the concentration of heavy metals not normally found in the surface rocks of the Earth. One of these, iridium, is common in metallic asteroids (and presumably the metallic core of the Earth), and when the Alverezes found “high concentrations” of it in clay minerals right at the K-T boundary (10 times the concentration above and below the clay), they proposed that this was proof positive that an asteroid caused the extinction of the dinosaurs. I was not convinced by this argument at that time. My problem with this evidence was that it was not collected in a random fashion. The Alverezes sampled just across the K-T boundary in only a few places on the planet. Who was to say that these so-called planet....
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This note was uploaded on 02/04/2012 for the course GLY 112 taught by Professor Haywick during the Spring '12 term at S. Alabama.
- Spring '12