North America, Triassic period. Image 4 of 9. Computer artwork of the Triassic period stage (approximately 251 to 199 million years ago) of a sequence showing the formation of the North American continent. The continents are slowly moved over the surface of the Earth by currents in the fluid mantle below the crust. Over millions of years the continents moved into the positions they are in today. The present day position of the United States of America (USA) is shown outlined in white. For North America at different points throughout prehistory, see images E402/163 to E402/171.
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