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Unformatted text preview: Clean Air Act of 1970 which banned the use of lead in gasoline. Lead will always be in the atmosphere but his efforts have greatly reduced its effects. 2. The KT boundary is a geological point referring to 65 million years ago when the dinosaurs and about half of the worlds other species of animals suddenly vanished from the fossil record. The iridium levels in the KT boundary were extremely high compared to normal iridium levels on earth. As iridium is abundant in most asteroids and comets, these high levels suggested that an asteroid struck the earth at the time of the KT boundary. This theory had been proposed in the past but there was never compelling evidence....
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- Winter '07