Environmental Problems, Their Causes, and Sustainability 1

ported from their sources by water, wind, or gravity todownstream, downwind, or downhill sites. These sedimentsare deposited in layers that accumulate overtime and increase the weight and pressure on underlyinglayers. A combination of pressure and dissolvedminerals seeping through the layers of sediment crystallizeand bind sediment particles together to formsedimentary rock.Examples are sandstone and shale (formed frompressure created by deposited layers of sediment),dolomite and limestone (formed from the compactedshells, skeletons, and other remains of dead organisms),and lignite and bituminous coal (derived fromplant remains). Some types of sedimentary rock are theresult of crystals precipitating out of or growing in solutionsand then being compacted in layers or dryingout to leave crystals behind. An example is rock salt,which we know as table salt or sodium chloride (NaCl).The third type is metamorphic rock, producedwhen a preexisting rock is subjected to high temperatures(which may cause it to melt partially), highpressures, chemically active fluids, or a combination ofthese agents. These forces can change or transform arock by reshaping its internal crystalline structure andits physical properties and appearance. Examples areanthracite (a form of coal), slate (formed when shaleand mudstone are heated), and marble (producedwhen limestone is exposed to heat and pressure).The interaction of physical and chemical processesthat changes rocks from one type to another is calledthe rock cycle (Figure 16-9). It recycles the earth’s threetypes of rocks over millions of years and is the slowestof the earth’s cyclic processes. It also concentrates theplanet’s nonrenewable mineral resources on which wedepend. Without the incredibly slow rock cycle youwould not exist.ErosionTransportationWeatheringDepositionSedimentary rockSandstone, limestoneIgneous rockGranite, pumice,basaltHeat, pressureCoolingHeat, pressure,stressMagma(molten rock)MeltingMetamorphic rockSlate, marble,gneiss, quartziteFigure 16-9 Natural capital: the rock cycle is the slowest of the earth’s cyclic processes. The earth’s materials are recycled overmillions of years by three processes: melting, erosion, and metamorphism, which produce igneous, sedimentary, and metamorphicrocks. Rock of any of the three classes can be converted to rock of either of the other two classes, or can be recycled within itsown class.http://biology.brookscole.com/miller14339