Smithsonian National Museum of Natural History: Dinosaurs PaleobiologyNational Museum of Natural HistorySmithsonian Institution
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What Is a Dinosaur? | Anatomy & Evolution | General Behavior | Where Did They Live?| Why Did They Go Extinct?

Why Did They Go Extinct?
Introduction | Alvarez Hypothesis: Origin and Evidence | Effects of the Asteroid Impact | Other Extinction Hypotheses | Deep-sea Evidence for the Impact Hypothesis | Post Extinction Recovery | References  

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Effects of the Asteroid Impact
The devastation caused by such an event is difficult to imagine. The asteroid would have hit with the force of 100,000 billion tons of TNT. This would have generated an earthquake one thousand times greater than the largest ever recorded, with winds of over 400 kph. A massive fireball would have boiled nearby seas, destroying everything for thousands of kilometers. Forests throughout most of North America and some of South America would have been flattened by the shock wave. Evidence of a giant tsunami has been found around the Gulf of Mexico and Caribbean, as well as in Spain and Brazil. It may have had an effect as far away as New Zealand. Map showing asteroid impact in Gulf of Mexico
Despite the enormity of the destruction from the initial impact, the dinosaurs and their contemporaries might have survived and eventually recovered, but the subsequent long-term effects of the blast were even more deadly. Ninety thousand cubic kilometers of debris would have been blasted into the atmosphere, some reaching into space only to re-enter at high speeds. This could have heated the atmosphere sufficiently to ignite global forest fires. While the heavier pieces of ejecta settled back down on Earth, fine dust particles would have remained in the atmosphere and significantly blocked sunlight, causing an effect called an “impact winter”. There is much debate about the duration and severity of the impact winter following the K/T impact, but the darkness and cold temperatures might have reduced photosynthesis and collapsed food chains globally.

The amount of carbon and sulfur contained in the rock at the impact site would have aggravated these devastating effects. As much as 100 billion tons of sulfur and 10 trillion tons of carbon would have been vaporized by the impact and blown into the atmosphere. The resulting sulfate aerosols would have stayed in the atmosphere for several years; the resulting carbon dioxide would have stayed airborne for several hundred years. Initially the sulfate aerosols would have contributed to global cooling by blocking out the sun, before precipitating as acid rain. After the dust and sulfates settled out and ended the cooling, global warming would have begun. The carbon dioxide levels, being two to three times normal, would have caused extreme greenhouse conditions, raising global temperatures by as much as 10°C. Although some life forms may have survived the years of darkness and freezing temperatures, many surely died out in the subsequent centuries of heat.

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