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American Museum of Natural History – Dinosaurs: Ancient Fossils, New Discoveries da_ExtinctionAtTheKT_SCRIPT_v47 - Script SECTION VI. Extinction [one plasma monitor, runs 4.5 minutes) Scientists: Denton Ebel AMNH Ph: 212/769-5381; E-mail: [email protected] Gerta Keller Dept of Geosciences 308 Guyot Hall, Princeton University, Princeton, NJ 08544. Ph: 609/258-4117; E-mail: [email protected] __________________________________________________________________ NARRATOR: One of the most puzzling questions about nonavian dinosaurs isn’t about how they lived. It’s about how they died. ON-SCREEN TITLE: Extinction at the K-T ON-SCREEN INTER-TITLE: IMPACT NARRATOR: There is no doubt that a meteorite—either an asteroid or comet— collided with Earth 65 million years ago. Denton Ebel: We know, from modeling of nuclear explosions and other physical models of the atmosphere, that an impact of this size would cause massive, massive devastation. Tidal waves, huge winds and hurricanes, dust that would block out the sun. The vapor would go high up into space and rain down on Earth as fine, condensed dust, depositing a layer, iridium-rich, all across the globe. Iridium is found at the K-T boundary all over the world in a thin layer. Iridium is not abundant in crustal rocks or volcanic rocks, but it is abundant in meteorites. ON-SCREEN INTER-TITLE: VOLCANISM NARRATOR: There is also evidence that massive volcanic eruptions occurred around this same time. The Deccan Traps is an immense volcanic plateau, over a mile thick in places, that covers much of western India. Its formation, over the course of hundreds of thousands of years, may have been as destructive as a sudden impact. Beginning around 66 million years ago, molten magma from deep inside Earth erupted to the surface, creating an active fissure hundreds of miles long. The massive volcanism unleashed huge concentrations of gases into the atmosphere. Gerta Keller: I study mass extinctions and their causes, and in particular, I look for evidence of meteor impacts and volcanism and how it affects life on Earth. I use foraminifera for such studies. 1 American Museum of Natural History – Dinosaurs: Ancient Fossils, New Discoveries da_ExtinctionAtTheKT_SCRIPT_v47 - Script Fossilized foraminifera, or forams, are tiny microorganisms. I use forams because they contain information about environmental changes in their shells. Because there are tens of thousands of forams in a single piece of rock like this, this can tell us a lot about the environment in which the dinosaurs and the forams lived. NARRATOR: Many species of forams declined and eventually became extinct soon after the Deccan Traps eruptions began. Such evidence suggests that the Deccan Traps volcanism altered global temperatures, causing major ecological changes around the globe for hundreds of thousands of years. ON-SCREEN INTER-TITLE: SEA LEVELS NARRATOR: Climate change over an even longer period of time also may have played a role. 100 million years ago, inland seas flooded Earth’s continents. Over the course of millions of years, these shallow inland seas gradually retreated to the lower ocean basins. Scientists theorize that without the temperature regulating effect of inland seas, climate across the globe became more extreme with hotter summers and colder winters. Many species declined over the last 10 million years of the Cretaceous. NARRATOR: From existing evidence, we know that at the end of their reign, dinosaurs faced long-term climate changes, intense volcanic activity and, finally, a massive extraterrestrial impact. All three profoundly would have affected life on Earth. And while most scientists agree that the impact played a major role in the K-T extinction, they continue to investigate the effects of volcanism and long-term climate change. As we continue to gather information and study clues from 65 million years ago, we come closer to revealing the complex picture of life—and death—at the K-T boundary. 2