Part 1 of 3. The history of North America, from how it was created to the evolution of life on the continent, is charted by Kirk Johnson of the Smithsonian Institution's National Museum of Natural History. First up: the forces that created North America. Johnson travels to the Grand Canyon, where billion year-old rock layers are observed; and visits Alaska, where a fossil proves that palm trees once flourished there. Also: a gigantic lava flows that once threatened to split the continent.
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