natural resourceA material or energy source that people take from nature and use, such as water, oil, copper ore, soil, wood or heat from inside Earth.A geologist studying a natural resource asks first what process concentrated it there and second how fast nature can replace it.
renewable resourceA resource that natural processes replace within about a human lifetime, such as surface water, a planted forest or the steady flow of heat from Earth's interior. It can still run short in a place where people use it faster than it is replaced.A hydrologist calls river water a renewable resource but still measures whether a city is taking more each year than the river carries.
nonrenewable resourceA resource that takes far longer than a human lifetime to form, such as petroleum, copper ore or thick fertile topsoil, so the supply shrinks as people use it.Because copper ore is a nonrenewable resource, a mine's output eventually falls and companies turn to recycling for more metal.
sustainableDescribes a way of using a resource that leaves enough for future generations: the rate of use is no greater than the rate at which the resource is replaced or recovered.Pumping an aquifer is sustainable only when the amount pumped each year is no larger than the amount that soaks back in.
groundwaterWater that has soaked into the ground and fills the pores and cracks in sediment and rock below the surface.During a dry summer the stream kept flowing because groundwater was seeping into it from the gravel beneath the valley.
aquiferA body of porous rock or sediment, such as gravel, sand or sandstone, that stores groundwater and lets it flow well enough to supply a well.The well driller stopped at 60 meters because the sandstone aquifer there yields more water than the clay above it.
rechargeThe water that reaches an aquifer by soaking down from rain, snowmelt, rivers or irrigation. The recharge rate is how much arrives per year.After three wet winters the recharge was enough to raise the water table by two meters.
petroleumCrude oil: a liquid mixture of hydrocarbons that formed over millions of years when the remains of tiny marine organisms were buried, heated and chemically changed deep in sedimentary rock.Petroleum migrated upward through the porous sandstone until a layer of shale stopped it.
geologic trapAn arrangement of rock layers, such as an upward fold or a fault, where a sealing layer stops rising oil and gas and holds them in a porous reservoir rock.The drilling team mapped a geologic trap by finding where the sandstone arched up beneath a shale cap.
oreRock that holds a valuable mineral or metal in a high enough concentration that mining it can pay.A rock with 0.5 percent copper counts as ore today, while a rock with 0.05 percent copper is just rock.
hydrothermal fluidHot water, often released by cooling magma or heated by it, that dissolves metals and carries them through cracks in rock, then leaves them behind as minerals when it cools.Quartz veins in the Sierra foothills mark the paths where hydrothermal fluid once flowed and dropped its gold.
geothermal energyEnergy from the heat of Earth's interior, carried to the surface by hot water or steam and used to warm buildings or to spin turbines that make electricity.Geothermal energy is easiest to capture where magma sits close to the surface, which is why plants cluster near plate boundaries and volcanoes.
