Transcript for Wrestling with Uncertainty, segment 05 of 16


For billions of years the restless plates that make up the outer crust of the Earth have shifted continuously. Since seven hundred million years ago, the crustal components of North and South America, Africa, and Europe have collided and split apart several times, and their surfaces have moved relative to sea level. In the past ocean waters have covered vast areas of the continents that are now relatively high and dry.

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These movements crumple the earth's crust, forming mountain ranges and basins. As erosion wears the mountains away, debris may slowly bury the hills as it fills adjacent basins with sediment or it may travel a much greater distance. Rivers of increasing size mix the mountain debris with material from plains and farmland, moving it to the edge of the continent and even beyond. Some of this sediment ends its journey in thick accumulations of mud and sand like the delta of the Mississippi. The basins that house these great masses of sediment contain our major petroleum resources. They form when plates converge or continents collide, when continents break apart, or when plates slide past one another. They cover a huge area of the United States.