Environmental Problems, Their Causes, and Sustainability 1

Collision between twoTectonic platecontinentsOceanic tectonic platePlate movementSubductionzoneSpreadingcenterOceanicOceanic crusttectonic platePlate movementOceanic crustOceantrenchContinentalcrustContinentalcrustMaterial coolsas it reachesthe outer mantleCold densematerial fallsback throughmantleMantleconvectioncellHot materialrisingthroughthe mantleTwo plates movetowards each other.One is subductedback into the mantleon falling convectioncurrent.Hot outercoreInnercoreMantleFigure 16-3 Natural capital: the earth’s crust is made up of a series of rigid plates, called tectonicplates, which move around in response to forces in the mantle.earth’s climate and concentrate many of the mineralswe extract and use.The theory of plate tectonics also helps explainhow certain patterns of biological evolution occurred.By reconstructing the course of continental drift overmillions of years, scientists can trace how species migratedfrom one area to another when continents thatare now far apart were still joined together. As the continentsseparated, populations became geographicallyand reproductively isolated, and speciation occurred.In other words, tectonic plates have played a major butmostly unnoticed role in the drama of life that continuesto unfold on our planetary home.What Types of Boundaries Occurbetween the Earth’s Plates? Moving Apart,Colliding, and SlidingThe earth’s tectonic plates move apart, pushtogether, and slide past one another.Lithospheric plates have three types of boundaries(Figure 16-5, p. 336). One is a divergent plate boundary,where the plates move apart in opposite directions.A second type is a convergent plate boundary,where the plates are pushed together by internalforces (Figure 16-5, middle). When an oceanic platecollides with a continental plate, the continental plate334 CHAPTER 16 Geology and Nonrenewable Mineral Resources