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  1. 1. viiiTopographic Map of the WorldCredit: NASA–SRTM
  2. 2. ix
  3. 3. xCredit: Mark Ernste
  4. 4. 1In our solar system, a single plan-et—the Earth—supports human life.World population is increasing. Yetfor the moment, the Earth remainsthe only home for the human species. Theway in which we care for this planet willaffect our future and the future of our chil-dren for generations to come.Seen from space, the Earth is largely ablue planet around which swirls of whiteclouds constantly move. The Earth’s blueareas are its oceans. Oceans account forapproximately 70 per cent of the Earth’stotal surface area; the remaining 30 percent is land. The total size of the terrestrialsurface is approximately 149 million km2(59.6 million square miles) (McNeill 2000;Grace n.d.).The Earth’s land surface is rich in itsvariety. The highest point on the Earth’sland surface is Mount Everest, a breathtak-ing 8 850 m (29 035 ft) above sea level.The lowest point is the Dead Sea, which is,on average, about 400 m (1 312 ft) belowsea level. Terrestrial surfaces gain and loseheat much more quickly than oceans and aregion’s distance from the equator dramat-ically affects its climate. Landsnearest the equator tend to bethe warmest. Those that lie inthe middle latitudes typicallyhave cooler climates, but arenot as cold as lands near thepoles. Some 20 per cent ofthe Earth’s terrestrial surface is covered bysnow. Another 20 per cent is mountainous.Just 30 per cent of the Earth’s land surfaceis suitable for farming.Most people are accustomed to see-ing the world around them as a relativelystable place, a generally nurturing environ-ment that has allowed the human race toexpand and develop in countless ways. Infact, the Earth is constantly changing, asis our understanding of it (Figure 1.1).Some changes to the Earth’s surface occuron microscopic levels. Other changes takeplace on a scale so large as to be almostinconceivable. Some types of change areinstantaneous, while other types occurslowly, unfolding over centuries, millennia,and even eons. Some changes are causedby the actions of people. Many others arepart of natural, inexorable cycles that canonly be perceived when cataclysmic eventsoccur or through painstaking research.1Credit: Blue Marble (NASA 2002)Introducing the PlanetA Story of Change“The only thing permanentis change.”— The Buddha (Siddartha Gautama)Figure 1.1: The Earth’s surface has changed dramaticallyover time—as has our understanding of it. Early ideasabout the shapes and locations of the continents, forexample, were far different from what is known about theland surface today.Credit:
  5. 5. 2Agents of Environmental ChangeFrom the Earth’s earliest beginnings, forcessuch as climate, wind, water, fire, earth-quakes, volcanic eruptions, and the im-pacts of meteors and comets have shapedthe Earth’s terrestrial environments. Thesesame forces are at work today and will con-tinue far into the future. In addition, everyliving thing influences its environment andis influenced by it. One species may lessenthe chances for survival of the organisms itconsumes for food. That same species, inturn, is affected by the actions ofother organisms.In order to survive, every organism musteither adapt to its environment or modifythe environment to make it more hospi-table. Humans are particularly adept atmodifying their environments. By their ac-tions and interactions with the landscape,for example, people can increase the rangeof certain plant species, either by modify-ing existing environments or by dispers-ing seeds into new ones. Environmentalmodifications made by people may bebeneficial or detrimental to a few or manyother species. Large-scale environmentalchanges may not benefit or be to the likingof people themselves (Nott 1996). As worldpopulation has increased and the scopeand nature of technology has changed,people have brought about environmentalchanges that may seriously impact theirfuture well-being and even survival.Humans began modifying their envi-ronment a long time ago (Table 1.1). Evi-dence of the existence of our first human-oid ancestors dates to the Pliocene Epoch,which extended from roughly 5 millionto 1.8-1.6 million years ago (Wikipedian.d.). These protohumans sought protec-tion from the elements and from preda-tors in natural shelters such as caves androck overhangs. Over time—and possiblyTable 1.1 – Approximate change of the Earth’s global vegetative cover in relation to human population(Adapted from McNeill 2000).Per cent of the Earth’s Vegetated Land AreaYear Forest and Human PopulationWoodland Grassland Pasture Cropland (Billions)8000 B.C. 51 49 0 0 0.0051700 A.D. 47 47 4 2 0.61900 43 40 10 6 1.61920 43 38 12 7 1.91940 41 35 16 8 2.31960 40 31 20 9 3.01980 38 26 25 11 4.41990 36 27 26 11 5.3Throughout the Earth’s history, events have occurred that dramatically impacted life on ourplanet. Five of those events stand out as having resulted in widespread extinctions, in some casesdestroying more than 90 per cent of all living things (Eldredge 2001):• Around 440 million years ago, a relatively severe and sudden global cooling caused amass extinction of marine life (little terrestrial life existed at that time). An estimated 25per cent of the existing taxonomic families were lost. (A family may consist of a few tothousands of species.)• Near the end of the Devonian Period, some 370 million years ago, a second majorextinction occurred. Roughly 19 per cent of the existing taxonomic families werewiped out. It is uncertain whether climate change was a driving factor.• About 245 million years ago, a third major extinction took place. Scientistsestimate that more than half (54 per cent) of all taxonomic families were lost.Climate change may have played a role, and that change may have been causedby a comet or meteor impacting the Earth.• At the end of the Triassic Period, around 210 million years ago, roughly 23per cent of existing taxonomic families suddenly became extinct. This eventoccurred shortly after the appearance of the first dinosaurs and mammals. Itscauses are not yet fully understood.• The fifth major extinction is the most well-known. It occurred about 65 mil-lion years ago at the end of the Cretaceous Period. The event led to the ex-tinction of all terrestrial dinosaurs and marine ammonites, along with manyother species occupying many different habitats. All told, approximately 17per cent of all taxonomic families vanished in a very short time. Currently,the most widely accepted hypothesis to explain this mass extinction is that acomet or other large extra-terrestrial object struck the Earth. Another viewproposes that a great volcanic event, or series of events, disrupted ecosys-tems so severely worldwide that many terrestrial and marine species rapidlysuccumbed to extinction.Five Major Events in the History of the EarthCredit: NRCSCredit: TopfotoCredit: Bigfoto2
  6. 6. 3influenced by the onset of colder weatherduring the Ice Ages—they created dwellingplaces for themselves in locations that hadno natural shelter.The oldest surviving traces of such ahuman-made habitation date to about2 million years ago from Olduvai Gorgein central Africa. There, a small circle ofstones was found stacked in such a way asto apparently have held branches in posi-tion. This early example of modificationof the environment was the work of Homohabilis, a tool–making human ancestor(Kowalski n.d.).The Pleistocene Epoch, including thePaleolithic and Mesolithic Periods (Wiki-pedia n.d.), is usually dated from the endof the Pliocene to 10 000 years ago. ThePaleolithic Period, or Old Stone Age, is aterm coined in the 19th century to definethe oldest period in the history of human-kind. It lasted for some 2.5 million years,from the time human ancestors createdand used the first stone tools to the end ofthe last glacial period some 10 000 yearsago. Homo erectus, thought by many to bethe direct ancestor of modern humans,lived from approximately 2 million toaround 400 000 years ago. As a species,Homo erectus was very successful in devel-oping tools that helped in adapting tonew environments. They were pioneers indeveloping human culture, ultimately mov-ing out of Africa to populate tropical andsub-tropical environmental zones in theOld World, possibly as early as 1.8 millionyears ago.Homo erectus may also have masteredthe use of fire around 1.6 million yearsago (Mcrone 2000). Fire is an exception-ally powerful tool. Since most animals,including large predators, are afraid offire, early humans quickly discovered thatcampfires offered protection from attackduring the night. Control of fire allowedthem to move into colder regions as it pro-vided warmth as well as security. Fire alsochanged the way food was prepared. Foodthat is cooked is less likely to carry diseaseorganisms and its softer texture makes iteasier to eat, enhancing the survival ofyoung children and old members ofa population.The use of fire almost certainly in-creased during the Paleolithic Period. Atthat time, humans were primarily hunter-gatherers. The role of fire in modernhunter-gatherer cultures gives us some ideaof its importance during the Paleolithicand how people then most likely usedFire—A Tool for HumankindFor thousands of years humans have used fire for:HuntingBy setting fire to parts of the landscape, people were able to drive gameanimals into smaller, more confined areas that made hunting easier. Firewas also used to drive animals into impoundments, chutes, river or lakes, orover cliffs. Fires also helped maintain open prairies and meadows by killingbushes and trees and encouraging rapid growth of grasses.Improving plant growth and yieldsSetting fires was a way to improve grass for grazing animals, both wild anddomestic, and to promote the growth of certain desirable plant species.ProtectionFire was used to protect human habitations.Collecting insectsSome tribes used “fire surrounds” to collect and roast crickets, grasshoppers,and moths. People also used fire smoke to quiet bees while collecting honey.Managing pestsFire was a handy tool for reducing or driving away insect pests such as fliesand mosquitoes as well as rodents. Fire was also effective for eliminatingundesirable plants.Warfare and signalingFire was both an effective defensive and offensive weapon. Offensively, it wasused to deprive enemies of hiding places in tall grasses or underbrush. Useddefensively, fire could provide cover during an escape. Smoke signals helpedalert tribes to the presence of possible enemies or to gather forces to combata foe. Large fires were set to signal a tribal gathering.Clearing areas for travelFires were sometimes started to clear trails through dense vegetation.Burning helped to improve visibility in forests or grasslands for huntingand warfare.Felling treesSinged or charred trees were easier to fell and to work with.Clearing riparian areasFire was used to clear vegetation from the edges of lakes and rivers.Managing cropsBurning was later used to harvest crops and collect grass seeds. Fire alsohelped prevent abandoned fields from becoming overgrown and was em-ployed to clear areas for planting.Credit: NRCS
  7. 7. 4it (Williams 2001). Fire was an importanttool in everyday life. It was also a tool withgreat potential to modify and changethe environment.The transition from Homo erectus toHomo sapiens—our modern human spe-cies—occurred approximately 300 000to 400 000 years ago. Throughout thePaleolithic Period, humans survived byexploiting resources in their environmentthrough subsistence activities such as fish-ing, hunting, and plant gathering. Fromethnographic studies of modern hunter-gatherers, we can infer that the basic socialunit of Paleolithic times was the band: aloosely bound, relatively small group (25people on average) formed by the volun-tary aggregation of a few families. Bandswere mobile, regularly changing residenceinside a delimited territory according tofluctuations in the abundance of differentfood sources. Inter-regional migrations,such as those within the WesternHemisphere, probably took place duringthis time.This mobile life was punctuated by epi-sodes of reunion, when several allied bandswould meet and perform religious ceremo-nies. Such occasions would have provideda time and place for the transmission oftechniques and artistic fashions, promotingtheir spread across vast expansesof territory.Some 10 000 years ago, a new geologicaltime period, the Holocene, began. Worldsea levels rose about 35 m (116 ft) in theearly Holocene due to melting glaciers. Asthe ice melted and glaciers receded, manyland areas that had been depressed byglacial weight slowly rose as much as 180m (594 ft) above their late-Pleistocene andearly-Holocene levels. Both sea-level riseand depressions in the landscape allowedtemporary ocean-water incursions intoregions that are today far from any sea.Climatic shifts also were very large duringthis period. Habitable zones expandednorthwards. Large, mid-latitude areas suchas the Sahara that were previously produc-tive became deserts. At the start of theHolocene, large lakes covered many areasthat are now quite arid.Animals and plants did not undergomajor evolutionary changes during theHolocene, but there were significant shiftsin their distribution. Several types of largemammals including mammoths, mast-odons, saber-toothed cats, and giant slothswent extinct in the late Pleistocene andearly Holocene. Ecological “islands” of iso-lated species were created throughout theworld, including high-altitude remnantsof cooler, previously regional climateecosystems.The period from 10 000 to 5 000 or4 000 years ago is recognized as the Neo-lithic Period (New Stone Age). It waspreceded by the Mesolithic Period (MiddleStone Age), which roughly correspondswith the beginning of the Holocene. TheMesolithic Period formed a transitionbetween the Paleolithic and NeolithicPeriods, that is, from the end of the Pleisto-cene to the introduction of agriculture inany given geographical region(Wikipedia n.d.).The size of the world’s human popula-tion 10 000 years ago is estimated to havebeen around 5 million (IPC 2003a). Thisperiod saw the beginning of agricultureand the domestication of animals. Peoplelearned to cultivate crops rather than tosimply gather what nature provided in thewild and to tame and raise animals such assheep, goats, cattle, horses, and dogs, rath-er than hunt them. These activities helpedensure better food supplies and resultedin wide-ranging cultural consequences.Permanent communities were now estab-lished, since people were no longer depen-dent on following wild animals or movingwith the seasons. Day-to-day existencechanged from a life of nomadic foragingto one of permanence. This allowed someindividuals to explore tool production torefine rude stone tools and improve imple-ments such as stone-blade knives, bow drillswith flints for starting fires, fish hooks,axes, and plows. Other people found timeto improve agricultural and pastoral tech-niques, enabling communities togrow more food and tend livestockmore effectively.The cultivation of plants and the do-mestication of animals dramaticallyCredit: Topfoto
  8. 8. 5impacted human lifestyles during theNeolithic Period. People left their tempo-rary rock and wooden shelters and beganto build more permanent homes in closeproximity to their farms and gardens,where they started producing cereal grainswhich became an important part of theirdiet (Wadley and Martin 1993).The Neolithic Period marked the begin-ning of true civilization, laying the foun-dations for major developments in socialevolution such as permanent settlements,village life, formalized religion, art, archi-tecture, farming, and the production ofadvanced tools and weapons.AgricultureThe first cultivation of wild grains some12 000 to 10 000 years ago turned hunter-gatherers into farmers. The transition gavepeople a more abundant and dependablesource of food and changed the worldforever (Wilford 1997). The practice ofagriculture first developed in the FertileCrescent of Mesopotamia (part of present-day Iraq, Turkey, Syria, and Jordan). Thisregion, which was much wetter then thanit is today, was home to a great diversity ofannual plants and 32 of the 56 largest seed-producing grasses (Primal Seeds n.d.).Around 11 000 years ago, much of theEarth experienced long dry seasons, prob-ably as a consequence of the major climatechange that took place at the end of thelast Ice Age. These conditions favoredannual plants that die off in the long dryseason, leaving a dormant seed or tuber.Such plants put more energy into produc-ing seeds than into woody growth. Anabundance of readily storable wild grainsFigure 1.2: The Earth’s climate system involvescomplex interactions among many elements andprocesses. Source: Topfoto
  9. 9. 6and other edible seeds enabled hunter-gatherers in some areas to form perma-nently settled villages at this time (PrimalSeeds n.d.).Theories vary as to how agriculturecame into being. Some scientists argue thatrising global temperatures created favor-able conditions for agriculture. Otherspropose that an increase in seasonalityafter the last Ice Age encouraged people todomesticate plants. Still other researchersmaintain that ecological changes, socialdevelopment, or a growing human popula-tion intensified the exploitation of specificplant species (Baldia 2000).Another suggestion is that an increasein carbon dioxide (CO2) on a global scalemay have played a critical role in bringingabout the synchrony of agricultural originsaround the globe (Sage 1995). Studieshave shown that a rise in atmospheric CO2levels would have increased productivityof many plants by as much as 50 per cent.Furthermore, the water efficiency of culti-vated plants increased, giving these plantsa competitive advantage over wild species.A few scientists have proposed that cli-matic changes at the end of the last glacialperiod led to an increase in the size andconcentration of patches of wild cereals incertain areas (Wadley and Martin 1993).Increased availability of cereal grainsprovided people with an incentive to makea meal of them. Those who ate sizableamounts of cereal grains inadvertentlydiscovered the rewards of consuming thevarious chemical compounds that cerealgrains contain. As processing methodssuch as grinding and cooking made cerealgrains more palatable, greater quantitieswere consumed.At first these patches of wild cerealswere protected and harvested. Peoplebegan to settle around these food sources.They gradually abandoned their nomadiclifestyle and began working together morecooperatively. Later, land was cleared,seeds were planted, and seedlings tendedto increase the quantity and reliability ofcereal grain supply.The rise of more permanent settle-ments intensified the domestication ofanimals. The first candidate for domestica-tion, around 11 000 years ago, was prob-ably the dog. The cow was domesticatedaround 10 000 years ago. Goats, sheep, andpigs were added to the growing list of do-mesticated animals around 8 000 years agoin western Asia. The horse was first domes-ticated in northern Russia around 4 000years ago. Local equivalents and smallerspecies were increasingly domesticatedfrom 2 500 years ago (Wikipedia n.d.).Farming and herding facilitated thegrowth of larger settled human popula-tions and led to increased competition forproductive lands, laying the foundation fororganized warfare. Food surpluses freedpeople to specialize in various crafts, suchas weaving, and, in larger communities,supported the emergence of a privilegedelite class. Archaeologists and historiansagree that the rise of agriculture, includingthe domestication of animals for food andlabor, produced the most important trans-formation in the interaction between theenvironment and human culture since thelast Ice Age—perhaps the most significantdevelopment in human history since thecontrol of fire (Wilford 1997).Other milestones in human history thatbenefited people and changed the envi-ronment include:The Bronze and Iron Ages (roughly 3300B.C. to 0 A.D.)The world population approximately 5 000years ago is estimated to have been about7 million (IPC 2003a). This period saw theintroduction of metallurgy and mining, theinvention of the wheel, and the domestica-tion of the horse.Classical Greece and Rome (0 to about500 A.D.)The world population at the beginning ofthis period was roughly 200 million (IPC2003a). During this period, glass was in-vented and map-making developed.Middle Ages to the Renaissance (500 toabout 1700)By this point, world population had grownto about 250 million (IPC 2003a). Theclock, compass, telescope, thermometer,and barometer were developed, enablingpeople to expand their knowledge of theEarth and the Universe.The Industrial Revolution (1700 – present)By 1700, world population had risen toabout 600 million (IPC 2003a). This pe-riod witnessed the development of mecha-nization and the beginning of serious airpollution. Industrial changes also led to anagricultural revolution.The Agricultural Revolution (1750 – 1900)By 1750, world population had risen to 790million (IPC 2003a). In many countries theway in which farmers produced food be-gan to change. New crops were exploitedusing new technologies such as the seeddrill and the iron plow. These methods ofproduction produced greater quantitiesof more nutritious foods, thereby improv-ing peoples’ diets and health. Better, moreefficient farming methods also meant thatfewer people were needed to farm. As aresult, unemployed farmers formed a largenew labor force.Credits: NOAACredit: Ed Simpson
  10. 10. 7The Green Revolution (1944 – present)In 1944, world population reached 2 350million (Anon n.d.). A breakthrough inwheat and rice production in Asia in themid-1960s, which came to be known as theGreen Revolution, symbolized the prog-ress of agricultural science as it developedmodern techniques for use in developingcountries. The Green Revolution had itsorigin in Mexico, where a “quiet” wheatrevolution began in the 1940s(Borlaug 2000).The goal of the Green Revolution wasto enhance the efficiency of agriculturalprocesses in order to increase the produc-tivity of crops, thereby helping developingcountries to meet the needs of their grow-ing populations. The Revolution consistedof three primary elements: continuing ex-pansion of farming areas, double-croppingexisting farmlands, and using geneticallyimproved seeds.The Green Revolution has been criti-cized on several grounds. But the primaryarguments against it involve environmentalconcerns, including:loss of biodiversity and food quality;fossil fuel dependence: while agriculturaloutput increases, the amount of en-ergy used to produce a given crop alsoincreases and at a greater rate, so thatthe ratio of crops produced to energyexpended decreases over time;pollution: fertilizer, pesticide, and her-bicide use, along with chemical runoff,continues to be a significant sourceof pollution;land degradation: critics charge thatGreen Revolution practices destroy soilquality in the long term. This resultsfrom a variety of factors, includingincreased soil salinity due to heavy ir-rigation, “burning” of the soil throughexcessive use chemical fertilizers,destruction of beneficial soil microbesand other organisms, soil erosion, andloss of valuable trace elements. Soildegradation can lead to an increasedreliance on chemical inputs to compen-sate for deteriorating soil quality—aprocess that may ultimately fail.The Green Revolution also introducedmajor changes into a world where the ma-jority of people still depended on farmingfor their livelihood. The new techniquesencouraged large-scale industrial agricul-ture at the expense of small farmers whowere unable to compete with high-effi-ciency Green Revolution crops. This hascaused massive displacement and povertyas farmers who were unable to competehave moved into urban areas to find work.Many farmers have also lost their lands tolarge agricultural companies that, by con-trast, are managing Green Revolution tech-niques to their benefit (Wikipedia n.d.).The Present DayWorld population now stands at 6 billionpeople (IPC 2003b). While global resourc-es were sufficient to support the Earth’shuman population as a whole prior to theIndustrial Revolution, individual groups oreven entire civilizations sometimes reachedenvironmental limits for a particular re-source; a number collapsed as a result ofunsustainable hunting, fishing, logging,or land use practices. The ever-increasingcultural globalization of the 20th and 21stcenturies has brought with it globalizationof resource degradation, making currentenvironmental problems an issue for theCredit: TopfotoCredit: Topfoto
  11. 11. 8entire world rather than for individual, isolatedgroups. Although perceived environmental limitscan sometimes be overcome, neither science nortechnology has yet made possible unlimited sup-plies of natural resources or depositories for waste(Casagrande and Zaidman 1999).Moderate projections put world population ataround 8 300 million by 2025 (Figure 1.3), withthe hope that it will stabilize at roughly 10 000 to11 000 million by the end of the century. It tookapproximately10 000 years to expand global food productionto the current level of about 5 000 million metrictonnes per year. By 2025, production must be nearlydoubled. In order to feed the world’s people through2025, an additional 1 000 million metric tonnes ofgrain must be produced annually. Most of this increasewill have to be supplied by improving crop yields on landalready in production.This will not be possible unless farmers worldwide have ac-cess to existing high-yield crop production methods as well asbiotechnological breakthroughs that increase the yield, depend-ability, and nutritional quality of our basic food crops (Borlaug2000).Human beings have been very successful in exploitingthe Earth’s resources. In the process, however, they havebrought about major changes in the Earth’s ecosystems,especially in recent years:• half the world’s wetlands were lost during the lastcentury;• logging and land use conversion have reducedforest cover by at least 20 per cent, and possiblyas much as 50 per cent;• nearly 70 per cent of the world’s majormarine fishstocks are either over-fished or beingfished at the biological limit;• over the last half century, soil deg-radation has affected two-thirds ofthe world’s agricultural land. It isestimated that each year some25 000 million metric tonnesof fertile topsoil—theequivalent of all ofthe wheat fields inFigure 1.3: Earth’s shrinking biosphere land area (ha)/capita1900-2000 ADCurrently, the Earth is the only home we have. With each new personadded to our growing population, the amount of our living spacedecreases. Thus we have less land available but an increasing need tofeed more people. This puts more pressure on our limited resourcesand exacerbates changes in the environment. Source: Lund and Iremon-ger 20008
  12. 12. 9ReferencesAnon. (n.d.). World population through the years. on 19 March 2004.Baldia, M. O. (2000). The origins of agriculture. Version 2.01. on19 March 2004.Borlaug, N. E. (2000). The Green Revolution revisited and the roadahead. Special 30th Anniversary Lecture, The Norwegian NobelInstitute, Oslo, Norway, September 8, 2000, 23. lecture.pdf on 1August 2004.Casagrande, J. and Zaidman, Y. (1999). Defining a new balancebetween humans and the environment. Changemakers. on18 March 2004.Eldredge, N. (2001). The sixth extinction. ActionBioscienceJournal. http://www.actionbioscience. org/newfrontiers/el-dredge2.html on 19 March 2004.Grace, J. (n.d.). World Forests and Global Change. University ofEdinburgh, The Institute of Ecology & Resource Management,Edinburgh, UK. http://www.ierm. on 7 October 2004.IPC (2003a). Historical estimates of world population. U.S. CensusBureau, Population Division, International Programs Center,Cambridge, UK. http://www.census. gov/ipc/www/worldhis.html on 19 March 2004.IPC (2003b). Total midyear population for the world: 1950-2050.U.S. Census Bureau, Population Division, International Pro-grams Center, International Data Base, Cambridge, UK. on 19 March 2004.Kirby, A. (2000). Humans stress ecosystems to the limit. BBC News,UK. on 19March 2004.Kowalski, W.J. (n.d.). on 19 March 2004.Lund, H.G. and Iremonger, S. (2000). Omissions, commissions, anddecisions: the need for integrsted resource assessments. ForestEcology and Management, 128(1-2): 3-10.McNeill, J.R. (2000). Something new under the sun – An environ-mental history of the twentieth century world. W.W. Norton &Company, New York, USA, 421.Mcrone, J. (2000). The discovery of fire. New Scientist. May 2000. on 18 March 2004.NASA (2002). Blue Marble: Land Surface, Shallow Water, andShaded Topography. on 18 August 2004.Nott, A. (1996). Environmental Degradation. on 6 October 2004.Primal Seeds (n.d.). Agriculture Origins. on 19 March 2004.Recer, P. (2004). Many species at risk of extinction. ResearchStudy. Associated Press. on 19 March 2004.Sage, R.F. (1995). Was low atmospheric CO2 during the Pleistocenea limiting factor for the origin of agriculture? Global ChangeBiology, 1:93-106. http://www.greeningearthsociety. org/Ar-ticles/origins.htm on 23 March 2004.Tapestries and More. on 12 May 2004.UNEP (2002). Global Environment Outlook 3 (GEO3) – Past,present and future perspectives. Earthscan, London, UK, 446. on 4 March 2004.US Global Change Research Program (2004). Our ChangingPlanet: The U.S. Climate Change Science Program for FiscalYears 2004 and 2005, 8. on 13 October 2004.Wadley, G. and Martin, A. (1993). The origins of agriculture – a bio-logical perspective and a new hypothesis. Australian Biologist6: 96 – 105. http://www.veganstraight- on 19 March 2004.Wikipedia (n.d.). The free encyclopedia. on 18 March 2004.Wilford, J. N. (1997). New clues show where people made the greatleap to agriculture. The New York Times Company. on 19 March 2004.Williams, G. W. (2001). References on the American Indian useof fire in ecosystems. U.S. Department of Agriculture: ForestService, Washington, DC, USA. http://www. on 15 March 2004.Australia— is lost globally (Casagrandeand Zaidman 1999);• each year, an estimated 27 000 speciesdisappear from the planet—approxi-mately one every 20 minutes (Casa-grande and Zaidman 1999);• the Earth now appears to be experienc-ing a sixth mass extinction event thatbegan about 50 000 years ago with theexpanding role of humans in the world(Recer 2004). Unlike past events, thismass extinction is being caused by hu-man activities such as transforming thelandscape, overexploiting species, pol-lution, and alien species introductions(Eldredge 2001);• dams and engineering works have frag-mented 60 per cent of the world’s largeriver systems. They have so impeded wa-ter flow that the time it takes for a dropof water to reach the sea has tripled;• human activities are significantly al-tering the basic chemical cycles uponwhich all ecosystems depend(Kirby 2000).Historian J.R. McNeill recently wrote(McNeill 2000): “It is impossible to knowwhether humankind has entered a genuineecological crisis. It is clear enough that ourcurrent ways are ecologically unsustainable,but we cannot know for how long we canyet sustain them or what might happen ifwe do.” In the past, humanity trod relative-ly lightly on the Earth, even though civiliza-tions were intensely concentrated in someplaces such as Mesopotamia and the NileRiver valley. Today, however, the evidencefrom space shows signs of the human pres-ence in almost every corner of the planet.Global concern about the environmentand the fate of the Earth emerged in the1970s, as did international initiatives toaddress those concerns. In roughly the past30 years, the environment has borne thestresses imposed by a four-fold increase inhuman population and an eighteen-foldincrease in world economic output (UNEP2002). Not surprisingly, when scientistscompare recent satellite images of theEarth’s surface with those taken one or sev-eral decades ago, the impact people havehad on the planet is obvious andoften disturbing.This atlas vividly illustrates some of thechanges the human race has brought abouton the Earth—both good and bad—overthe past 30 years. In doing so, it also servesas an early warning for environmentalevents that may occur. We hope it will beuseful as a basis for developing policy deci-sions and promoting individual actions tohelp sustain the Earth and ensure the well-being of its inhabitants.Credit: Topfoto9