Environmental Problems, Their Causes, and Sustainability 1

distribution facilities. Compare humanresources, natural resources.manure See animal manure, greenmanure.marasmus Nutritional deficiency diseasecaused by a diet that does not have enoughcalories and protein to maintain goodhealth. See kwashiorkor, malnutrition.marginal benefit Increase in benefit whena seller produces one more unit of a productor service. Compare marginal cost.marginal cost Increase in total cost resultingfrom producing one more unit of a goodor service. Compare marginal benefit.mass The amount of material in anobject.mass depletion Widespread, often globalperiod during which extinction rates arehigher than normal but not high enough toclassify as a mass extinction. Compare backgroundextinction, mass extinction.mass extinction A catastrophic, widespread,often global event in which majorgroups of species are wiped out over a shorttime compared with normal (background)extinctions. Compare background extinction,mass depletion.mass number Sum of the number ofneutrons (n) and the number of protons (p)in the nucleus of an atom. It gives theapproximate mass of that atom. Compareatomic number.mass transit Buses, trains, trolleys, andother forms of transportation that carrylarge numbers of people.material efficiency Total amount of materialneeded to produce each unit of goods orservices. Also called resource productivity.Compare energy efficiency.matter Anything that has mass (theamount of material in an object) and takesup space. On the earth, where gravity ispresent, we weigh an object to determine itsmass.matter quality Measure of how useful amatter resource is, based on its availabilityand concentration. See high-quality matter,low-quality matter.matter-recycling economy Economy thatemphasizes recycling the maximumamount of all resources that can be recycled.The goal is to allow economic growth tocontinue without depleting matterresources and without producing excessivepollution and environmental degradation.Compare high-throughput economy, lowthroughputeconomy.mature community Fairly stable, selfsustainingcommunity in an advanced stageof ecological succession; usually has adiverse array of species and ecologicalniches; captures and uses energy and cyclescritical chemicals more efficiently than simpler,immature communities. Compareimmature community.maximum sustainable yield See sustainableyield.MDC See developed country.median lethal dose (LD50) Amount of atoxic material per unit of body weight oftest animals that kills half the test populationin a certain time.megacity City with 10 million or morepeople.meltdown The melting of the core of anuclear reactor.mesosphere Third layer of the atmosphere;found above the stratosphere. Comparestratosphere, troposphere.mesotrophic lake Lake with a moderatesupply of plant nutrients. Compareeutrophic lake, oligotrophic lake.metabolism Ability of a living cell ororganism to capture and transform matterand energy from its environment to supplyits needs for survival, growth, and reproduction.metamorphic rock Rock producedwhen a preexisting rock is subjected to hightemperatures (which may cause it to meltpartially), high pressures, chemically activefluids, or a combination of these agents.Compare igneous rock, sedimentary rock. Seerock cycle.metastasis Spread of malignant (cancerous)cells from a tumor to other parts of thebody.metropolitan area See urban area.microclimates Local climatic conditionsthat differ from the general climate of aregion. Various topographic features of theearth’s surface such as mountains and citiestypically create them.microevolution The small geneticchanges a population undergoes. Comparemacroevolution.micronutrients Chemical elements thatorganisms need in small or even traceamounts to live, grow, or reproduce. Examplesare sodium, zinc, copper, chlorine, andiodine. Compare macronutrients.microorganisms Organisms such as bacteriathat are so small that they can be seenonly by using a microscope.micropower systems Systems of smallscaledecentralized units that generate1–10,000 kilowatts of electricity. Examplesinclude microturbines, fuel cells, and householdsolar panels and solar roofs.midsuccessional plant species Grassesand low shrubs that are less hardy thanearly successional plant species. Compareearly successional plant species, late successionalplant species.mineral Any naturally occurring inorganicsubstance found in the earth’s crust asa crystalline solid. See mineral resource.mineral resource Concentration of naturallyoccurring solid, liquid, or gaseousmaterial in or on the earth’s crust in a formand amount such that extracting and convertingit into useful materials or items iscurrently or potentially profitable. Mineralresources are classified as metallic (such asiron and tin ores) or nonmetallic (such as fossilfuels, sand, and salt).minimum-tillage farming See conservation-tillagefarming.minimum viable population (MVP) Estimateof the smallest number of individualsnecessary to ensure the survival of a populationin a region for a specified timeperiod, typically ranging from decades to100 years.mixture Combination of one or more elementsand compounds.model An approximate representation orsimulation of a system being studied.molecule Combination of two or moreatoms of the same chemical element (suchas O 2 ) or different chemical elements (suchas H 2 O) held together by chemical bonds.Compare atom, ion.monoculture Cultivation of a single crop,usually on a large area of land. Comparepolyculture, polyvarietal cultivation.more developed country (MDC) Seedeveloped country.mountaintop removal Type of surfacemining that uses explosives, massiveshovels, and even larger machinery calleddraglines to remove the top of a mountainto expose seams of coal underneath amountain. Compare area strip mining, contourstrip mining.multiple use Use of an ecosystem such asa forest for a variety of purposes such astimber harvesting, wildlife habitat, watershedprotection, and recreation. Comparesustainable yield.municipal solid waste Solid materialsdiscarded by homes and businesses in ornear urban areas. See solid waste.mutagen Chemical or form of radiationthat causes inheritable changes (mutations)in the DNA molecules in the genes foundin chromosomes. See carcinogen, mutation,teratogen.mutation A random change in DNA moleculesmaking up genes that can yieldchanges in anatomy, physiology, or behaviorin offspring. See mutagen.mutualism Type of species interaction inwhich both participating species generallybenefit. Compare commensalism.native species Species that normally liveand thrive in a particular ecosystem. Compareindicator species, keystone species, nonnativespecies.natural capital See natural resources.natural gas Underground deposits ofgases consisting of 50–90% by weightmethane gas (CH 4 ) and small amounts ofheavier gaseous hydrocarbon compoundssuch as propane (C 3 H 8 ) and butane (C 4 H 10 ).natural greenhouse effect Heat buildupin the troposphere because of the presenceof certain gases, called greenhouse gases.Without this effect, the earth would benearly as cold as Mars, and life as we knowit could not exist. Compare global warming.natural ionizing radiation Ionizingradiation in the environment from naturalsources.GLOSSARYG11