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00:00Around the world lie
00:28by the ruins of once great civilizations.
00:37In Colorado and New Mexico, Native Americans built thriving towns.
00:48In the rain forests of Central America, the ancient Maya created magnificent city-states.
00:54Three million people once lived here.
01:01In the earliest cradle of civilization, Mesopotamian farmers once made these deserts bloom.
01:10Halfway around the world in California are clues to understanding the fall of Mesopotamia,
01:16as farmers here struggle to overcome a threat to this fertile land.
01:24The ruins of ancient societies may hold keys to our own survival, as out of the past, archaeologists
01:30explore one of the greatest of mysteries, the decline and fall of the great civilizations.
01:42The end of the world
01:48The end of the world
01:52The end of the world
01:56Ignition and liftoff, liftoff.
02:03For more than five millennia, mankind has seemed to dominate the Earth, both creating
02:15and destroying great civilizations.
02:22Each of these human experiments has changed the planet.
02:25This high vantage point brings us a new and sobering view.
02:43For the first time, we see our world as finite, limited.
02:49On the darkened face of the Earth, the lights of cities record the expansion of the human race.
02:55Just fifty years ago, two billion people lived on Earth.
02:59Today, our global population has reached five billion.
03:03Within the next generation, it'll double once more.
03:07Our exponential growth now threatens the very resources that sustain life.
03:16The abandoned ruins of ancient societies hold clues to our survival.
03:20But to learn from our past, we must discard the romantic image of these earlier and simpler societies.
03:31A commonly held notion among the public at large, and also among some of my anthropological colleagues,
03:37is that non-Western peoples live in harmony with nature, but they have relatively stable environmental relationships.
03:45What archaeology teaches us is that that's not true.
03:52In the New World, human beings appeared for the first time more than 10,000 years before the birth of Christ.
04:01Over the millennia, grand city-states emerged in the tropics of Mexico, Guatemala, and Honduras.
04:10This is the realm of the ancient Maya.
04:15They built magnificent cities and decorated them with the portraits of their kings.
04:20These are the ruins of Copan in Honduras.
04:27The mystery of the rise and fall of these Maya kingdoms has fascinated archaeologists for centuries.
04:34Now they're able to rebuild the ancient city of Copan, a 30-acre maze of ball courts and plazas, monumental sculpture and colossal stairways.
04:46Intricate and beautiful Maya glyphs have been deciphered to reveal the history of a grand dynasty that once ruled here.
04:57The Copan dynasty endured for almost 400 years, recording their triumphs on elaborately carved altars and stele.
05:05Carved here, too, is a record of their downfall.
05:08This is altar L. It's the last carved monument at the site and, in fact, represents a metaphor for the political collapse of this city.
05:15On it, we see an attempt on the part of the 17th would-be ruler to copy the great dynastic altar, altar Q, of the 16th ruler.
05:23But in order to get to the throne part, you have to go to the back side of the altar.
05:27In so doing, what you discover is that the top and these two sides of altar L were never even carved.
05:34And, in fact, on the back side where you would expect to find the rest of the text saying seated as king, you just have a blank panel.
05:41They never finished carving the text.
05:43So on that date, on the 10th of February in AD 822, when the sculptor dropped his tools and walked away,
05:50that was effectively the end of the Copan dynasty.
05:54The fall of the Maya dynasties was not only dramatic, but widespread.
06:02Within 150 years, many of the grandest Maya palaces lay abandoned.
06:08At Palenque, Copan, Tikal, across a landscape the size of England, all was in ruin.
06:24All over the lowlands, about 800 AD, in hundreds of Maya sites, they stopped erecting dated monuments, and they stopped building palaces and temples.
06:36This was an extraordinary historical event.
06:39A population of three million people or more drops down to a few tens of thousands.
06:43And it looked as though this happened over a period of only a century or a century and a half, according to the accepted chronology.
06:49The apparent swiftness of the collapse suggests a disaster, a plague, drought or warfare.
07:06Could the Maya have been destroyed by foreign invaders?
07:11Here in Mexico City is a vivid example of what often happens when one society conquers another.
07:24The Mexican National Palace stands in the center of the city.
07:34In its courtyard, the murals of Diego Rivera depict the Spanish conquest of the Aztecs.
07:43With guns and cannon, horses and armor, the conquistadors of Hernan Cortes attacked the armies of the Aztec emperor Montezuma.
07:51For a time, the Aztec orders of the Eagle and the Jaguar repelled the assault.
08:01But the Aztecs' traditional Indian adversaries joined forces with the Spanish.
08:10The alliance destroyed the Aztec empire.
08:15The Spanish built Mexico City on top of the ruins of the Aztec capital.
08:20In 1978, excavations for electric lines first uncovered Aztec sculptures, including this huge carving of the moon goddess.
08:33Today, archaeologists have revealed the capital of the ancient Aztec empire beneath Spanish streets.
08:39They've reconstructed a great temple that was rebuilt and enlarged many times by the Aztecs.
08:49The ruins of the temple lie beneath the main Spanish plaza called the Zocala.
08:55I think the Zocala of Mexico City is the most exciting place on earth.
09:05In front of me you can see the material remains of three successive civilizations.
09:09The great temple of the Aztecs, the cathedral, a symbol of Catholic Spain, and in the distance the Torre Latino, which is a symbol of modern industrial Mexico.
09:20Prior to the Aztecs, we have evidence of two earlier civilizations in the same valley.
09:25So we have successive civilizations, one replacing the other, for 2,000 years.
09:32And this is the normal pattern that archaeologists and historians find when they study a region of the world.
09:38What changes are the elite levels of culture, the political institutions of power, and the religious ideology that validates that power.
09:47But there is also a continuity. The fact that we have a city here through three successive civilizations is an example of that.
09:55And that continuity exists because the changes only occur at the top.
09:59The bottom level, the working class, persists and provides the labor and the goods to support the system.
10:08With stones from their own temples, Aztec laborers were forced to build the Spanish cathedral.
10:17A new religion replaced the old. But the cathedral is also a symbol of continuity in Mexico.
10:24Many who kneel to pray here are direct descendants of the Aztecs.
10:34For the commoners, the Spanish conquest and the later Mexican revolution brought merely an end to one form of government and the imposition of another.
10:42It's a pattern repeated around the world.
10:51The collapse of Maya civilization, though, was quite different.
10:55Warfare and conquest cannot explain the total abandonment of these once grand cities.
11:03Even if warfare had taken many lives, the Maya population should have revived within a few generations.
11:08What could have caused such a widespread disaster?
11:15Two thousand miles from the Maya heartland, a similar puzzle intrigues archaeologists in the American Southwest.
11:24Nestled in the cliffs at Mesa Verde in Colorado are the derelict ruins of the Anasazi Indians, the ancient ones.
11:38At Chaco Canyon in New Mexico, the Anasazi built great residential and ceremonial centers.
11:43Sometime between the 11th and 13th centuries, all of these communities were abandoned.
11:53In the southwestern corner of Colorado, one group of Anasazi flourished at a place called Sand Canyon.
11:58Now overgrown with juniper and pinion, Sand Canyon Pueblo was once a thriving, densely populated town.
12:11Here, a team of archaeologists are excavating an Anasazi settlement.
12:14About 500 people once lived here in more than 400 rooms.
12:25The rooms are grouped around circular chambers called kivas, where the Anasazi practiced rituals.
12:31The rituals were secret, so the kivas were built below ground level and concealed beneath an earthen roof.
12:38Heavy beams like this one supported the roof. Curiously, many beams are charred. The kivas had been burned.
12:52I'm not sure what it means, but I can speculate that the burning of the kiva roofs was some type of closing down ritual for this village.
12:59We've seen that a few other places in the northern southwest at a time when there was a substantial movement of population out of an area.
13:10So I think that that's a possibility, that they intentionally burned the kivas when they left this area for good.
13:19The Anasazi often moved their villages, but usually only over short distances.
13:24To find out when the site was abandoned, a charred roof beam was sent to a laboratory for analysis.
13:35Ordinarily, when the Anasazi left a settlement, they took most of their material equipment with them.
13:42They weren't going very far, they might even take the roof beams.
13:45San Canyon Pueblo is really different.
13:47This is a little rectangular ceramic box found in the niche in the kiva.
13:56Every left, right was where it was ordinarily left when they abandoned that part of the site.
14:01Valuable little things like this ordinarily wouldn't be left by people.
14:06So the archaeological evidence suggests that the people of San Canyon deserted their Pueblo to migrate a great distance.
14:15What could explain this abandonment?
14:17Clues to the disappearance of the Anasazi can be found in the traditions still observed by their descendants.
14:36Corn is still revered as a gift from the gods.
14:38Until the year 500, the Indians of this area were nomadic hunters and gatherers of plants.
14:49Then they began to cultivate corn and live in settled communities.
14:55They were dry farmers, dependent on spring rains to germinate seeds and summer downpours to nourish growth.
15:02Anasazi ritual reflected the importance of corn for survival and in these arid soils the growth of corn depended on rain.
15:25This sample of wood contains a record of ancient rainfall patterns.
15:29The patterns are being decoded by archaeologist Jeffrey Dean at the University of Arizona.
15:37Thousands of samples of trees have been collected here.
15:43An extraordinary record of rainfall that extends back to the days of Christ.
15:48The vertical bands in each sample are growth rings.
15:52Tree growth is largely determined by moisture.
15:54Thick rings are created during years of high rainfall, thin rings during dry years.
16:01By measuring the thickness of the rings, Dean can recreate the pattern of rainfall for when the tree lived.
16:09By sampling thousands of trees from across the southwest, he has mapped the climate of ancient times.
16:15Tree rings from the Sand Canyon area have shown that from about 1200 to 1274 people experienced normal or above normal rainfall patterns, shown here in green.
16:29But low rainfall, shown in red, began in 1275 and lasted for 14 years.
16:36So I really think what happened was that people got in trouble here in the late 1200s with a severe drought.
16:46Some people tried to stick it out, didn't make it, perhaps suffered famines or other calamities, but probably the majority of people bailed out and joined related Pueblo peoples to the south.
17:01This was also a period of extremely high population density in that area, lots of people per square mile.
17:08And it came at the end of a long period of farming in that area that depleted the agricultural resource.
17:15Those three things put together created a situation that perhaps was almost unique in the history of that southwestern corner of Colorado.
17:25The collapse of Anasazi society was triggered by drought, an act of nature beyond their control.
17:35Population growth and depletion of this fragile, arid environment may also have been factors.
17:42It's often assumed that people like the Anasazi lived in harmony with nature.
17:47But how common was it for ancient societies to have over-exploited their environment and threatened their own survival?
17:58At the State University of New York in Stony Brook, a team of archaeologists is seeking answers.
18:04Elizabeth Stone and Paul Zimansky are studying the plans of an ancient Middle Eastern city they recently excavated.
18:10OK, so this must be the back wall of the palace and that you can kind of pick up on the photograph there.
18:14The city is called Mashkan Shapir.
18:17It's one of the scores of cities that thrived 4,000 years ago in the deserts of what is now Iraq.
18:23This is the realm of ancient Mesopotamia.
18:32Centred on grand palaces and temples, urban life emerged in an area that archaeologists call the first cradle of civilization.
18:40Today, the ruins of these cities lie crumbling in the dry desert earth.
18:48But how could civilization have emerged in such an arid environment in the first place?
18:54And what might have caused its destruction?
18:57Data from Mashkan Shapir is providing clues.
19:00We found a very large palace structure, which was filled with decorated baked clay pieces, showing the city's own god, Nergal, the god of death.
19:11There was a large temple area in which we found pieces of sculpture, life size and somewhat smaller, of animals, human beings, all of which were probably part of the temple furniture.
19:23They also found fish hooks, weights to hold down nets and fish spears, all evidence that there was once water here.
19:36Written tablets like these describe Mashkan Shapir as a major port.
19:40But the city was 20 miles from the Tigris River and 30 miles from the Euphrates.
19:47How could a major inland port survive in the desert so far from water?
19:57Stone began a search for the source of water.
20:00For a perspective not possible from the ground, she ordered a digital photograph of the area from a satellite.
20:05In this blow-up, you can see the perimeter of the site right here, the two harbors, one here and one less clear over here,
20:18which were fed by two main canals, one here and one here.
20:22The whole picture is one of a great deal of water at the site.
20:26In this view, you see one large channel here, which must have fed the site, which is located here.
20:32Tracing the channel upstream, we suddenly found that it had two sources, one coming here and the other here.
20:41The presence of the two channels explains not only how Mashkan Shapir could have had boat trade with both the Tigris and Frady systems,
20:50but also the large amount of water that was available there.
20:52The water flowed through a network of canals allowing irrigation, the lifeblood of civilization in this desert.
21:02Archaeological study of the canals presented an intriguing puzzle.
21:06Within several decades of their construction, many of the canals were abandoned and new ones built to take their place.
21:12Why would the Mesopotamians abandon these waterways after investing so much labour in them?
21:22Halfway around the world in the Central Valley of California is an important clue.
21:27As in Mesopotamia, the government here constructed an elaborate system of aqueducts and canals.
21:44Water from the nearby mountains has turned the fertile but arid San Joaquin Valley
21:49into one of the most productive agricultural regions on earth.
21:58This area of the San Joaquin Valley has the ability to continue to be the breadbasket for the world for many, many years to come.
22:06But in order to continue this abundant production here, we have to solve one enormous problem.
22:14Salt.
22:20Salts like sodium chloride and calcium carbonate are turning some of the world's most productive farms into saline wastelands.
22:28In many of the world's arid regions, salt is a natural component of soil and water.
22:33When irrigation water evaporates, salts are left behind, contaminating the soil.
22:40To prevent this, additional water must be applied to wash the salts down and away from the root zone.
22:51The great quantity of water cleanses the soil, but in the process it too becomes saline.
22:56Deep beneath these fields, layers of rock or clay form a barrier.
23:02With nowhere to go, the salt water rises towards the roots, inhibiting growth or killing the crop.
23:09In wells throughout the valley, technicians measure the short distance to the saline water table and test for the salt content.
23:15The salt water has risen almost to the surface beneath nearly a million acres.
23:30Experiments like this canal to take the saline water to the sea have largely failed.
23:35By the 18th century BC, civilization had largely abandoned southern Mesopotamia.
23:48Evidence of salt damage here can be found in ancient texts.
23:53Clay tablets like these describe a host of changes in harvests due to salt in the fields.
23:59Archeologists continue to debate the causes of this collapse, but one fact is clear.
24:07Irrigation and salinization contributed to the decline of city after city.
24:14In this cradle of civilization, humans demonstrated they could destroy their environment as quickly as they could master it.
24:25But there are no deserts in Central America.
24:28What can explain the Maya collapse?
24:31The majority of their cities flourished in a broad tropical rainforest, one of the wettest environments on Earth.
24:41Here, irrigation was insignificant and there is no evidence of climatic change.
24:47A drought simply cannot explain the Maya downfall.
24:49And there is no evidence of other natural disasters to have caused such a massive decline in population.
25:01For more than 150 years, scholars have studied the Maya.
25:06But for most of this time, they focused on the royal centers.
25:17At Copan, they have discovered the burial sites of kings and their retainers.
25:24We now know the names of each king in a long dynasty.
25:28And the date almost to the day when the dynasty ended.
25:32Over the years, the grand temples and palaces of the Acropolis have been reconstructed.
25:44But for all this impressive research, one essential question remained unanswered.
25:54When and how did the ordinary men and women disappear?
25:57This looks great. This area is so intensively used that we can use...
26:06To find out, archaeologists Bill Sanders and Dave Webster from Penn State University began a project in 1980 that would span a decade of work.
26:15Before we started the Copan project, we knew a great deal about Copan.
26:21And its history was very similar to that of many classic Maya sites.
26:25It was a long period of population growth, of political evolution, peaking around 800 A.D.
26:30And then the dynastic sequence ends shortly afterwards.
26:34And within a short period, the valley seems to have been abandoned.
26:37What we didn't know was anything about the factors and the mechanisms and the processes that produce this peculiar population history.
26:45What we decided to do was a series of excavations and surveys which would allow us to find out how big the population was,
26:52how it was distributed on the landscape, how those people made a living off of this landscape,
26:57what the various social classes and social groupings were,
27:00and finally, hopefully, to get enough chronological information to find out how long this whole process of fluorescence and decline required.
27:07Their goal was nothing less than the recreation of the entire society of ancient Copan.
27:16To understand what life had been like for the vast majority of the Maya, research teams fanned out through the valley.
27:22Here, far from the palaces of the kings of Copan, archaeologists discovered the ruins of thousands of buildings, the homes of the common farmers.
27:34The way ancient settlements are patterned on the landscape is an archaeological clue to how the Maya may have organized themselves and how they may have exploited their environment.
27:46To decipher the pattern, the team explored and mapped the entire valley, a monumental task of surveying more than 60 square miles.
27:58Today, all that remains of Maya dwellings are subtle changes in elevation, barely detectable to even a trained eye.
28:09Here's the corner.
28:10This was once the home of a rural Maya peasant.
28:16Perfecto.
28:18Three metres and 80 centimetres. Another good-sized mound. Okay. Here's where we came in.
28:29Together with surveys completed by earlier expeditions, the team mapped more than 4,500 house mounds.
28:36The map shows the extent of Maya population in the hillsides surrounding the royal centre, but it tells us nothing of when the population rose and fell.
28:47The sites would have to be dated.
28:54A sample of the house mounds is excavated to determine when people lived here and for how long.
29:00Ah, that's what we need. Nice piece of obsidian.
29:05To date the hundreds of sites, the team used an ingenious dating technique. The key to the technique is obsidian.
29:13Razor-sharp obsidian knives were found at almost every site.
29:19Each obsidian blade begins life as a delicate sliver chipped from a lump of natural glass. At the moment of creation, an invisible clock is started.
29:33Archaeologist Anne Freeter.
29:35When obsidian is first broken, it has a clean edge that absorbs hydrogen atoms from water at a known rate.
29:44It's the same kind of thing as if a piece of hard candy is left out.
29:48It will start to absorb a little bit of water and get softer and softer while the centre can still stay hard.
29:53Obsidian is basically doing the same thing.
29:55And the longer that it's exposed to the elements, the thicker the hydration rim actually gets.
29:59And you can measure it and figure out a date.
30:04The hydration layer is not visible to the naked eye, so a tiny section of the obsidian blade is magnified.
30:11What you're looking at is the hydration layer which runs right across the very edge of the obsidian where the hydrogen atoms have gone into the piece of obsidian.
30:19And it goes from this black line right here down to that black line right there and it runs all the way across the entire piece of obsidian.
30:26And it's that line that you actually measure.
30:31Although the technique is simple, it's time consuming.
30:35And right from the beginning, Freeter ran into problems with her dates.
30:39The Copan Valley was supposed to have been basically depopulated by around 850-900 AD.
30:48And some of our dates were as late as 1200 AD, 300 years later than they should have been.
30:53And this was making absolutely no sense.
30:57And we were convinced the dating technique had a problem in it.
31:01The prevailing theory of the Maya collapse envisioned a slow population growth until the fall of the dynasties in about the year 800,
31:09when most of the Maya were thought to have rapidly disappeared.
31:12But Freeter's obsidian dates suggested that people lived at Copan for at least an additional 300 years and population declined gradually.
31:25Either her dates or the current theories were wrong.
31:27In 1984, David Rue, a colleague of Anne Freeter, helped resolve the problem Freeter had encountered with her obsidian dates.
31:46He set out to study the impact of the Maya on their landscape by collecting samples of ancient pollen from the trees and crops that once grew here.
31:56Most plants reproduce by spreading their pollen on the winds.
32:12Some of it has fallen in this bog.
32:14As the Maya population grew, forests would have been cleared for cornfields.
32:21As the population declined, trees would have grown up again.
32:24Such changes in the ancient landscape should show up in Rue's pollen samples.
32:28As we pull up this sample in this pollen-coring tube, it's about seven meters below the current surface of this bog,
32:36we're essentially pulling up a sample of time in which we've got a preserved record of vegetational changes through pollen
32:45that's been deposited in these sediments for thousands of years.
32:48In his laboratory at Penn State University, Rue reconstructed the changes in vegetation by counting individual grains of pollen from dated levels in the core.
33:07In levels dated to about 800 AD, corn pollen appears in large quantities.
33:13Maya farming was at its peak.
33:14In later samples, he found increasing quantities of pine pollen.
33:21Pine trees would have been the first to reclaim abandoned cornfields.
33:27Finally, he found conclusive evidence of the end of Maya farming in the valley around 1200 AD.
33:34This is pollen from a tree in the mahogany family.
33:37This family is part of the plant community comprising the tropical deciduous forest.
33:42Very natural, high canopy, rainforest-type vegetation that would have occurred in the valley before the Maya were there and then after they left the valley.
33:52Based on our previous notions about the depopulation in Copan, we would have expected to see this forest reemerge by approximately 1000 AD or so.
34:01Our pollen analysis showed that this forest was still completely gone from the valley up to and after 1200 AD, a fact that indicated to us that people were still clearing the area for farms for 200 years after we had expected the area to be abandoned.
34:19As Roo pondered the mystery revealed by his pollen samples, he consulted with Anne Frieda.
34:26A light bulb went off in our minds one day and we realized, hey, this is the way it really was.
34:35People stayed here and they continued to grow crops for at least another 200 years.
34:42We sat there and said, what if it's right?
34:44If it's right, it means that the collapse was much more gradual.
34:48It means that a lot of our theories dealing with why the collapse occurred would have to be incorrect because they were based on a very sudden collapse as opposed to a gradual one.
34:57It's the two pieces of evidence meshing together and each making much more sense than they would have individually.
35:06This is a representation of settlement in 500 AD.
35:11Using Anne Frieda's dates, archaeologists could actually create a moving picture of the rise and fall of Copan.
35:17As the population expanded, so did the agricultural fields. As it receded, the forests returned to the valley.
35:30The evidence of a gradual process of population collapse seemed conclusive. A new theory would be required to explain it.
35:37Before we did the Obsidian Hydration Project here at Copan, most scholars thought that the Maya collapse was a very rapid process.
35:48Now this was a pretty spectacular historical event and it intrigued many scholars over the years.
35:54And there were probably as many explanations as there were archaeologists.
35:59The most enduring explanation over the years, however, has always been an ecological one.
36:03Something must have happened to these people in terms of their relationship to their physical and biological environment.
36:12Could the collapse have been caused by an ecological disaster?
36:16To support such a theory, Sanders had to first study the ability of the Maya to harvest energy from their environment.
36:23The ancient Maya, like most pre-industrial peoples, performed all the work using human muscular energy.
36:31And that energy was derived from maize, the staple crop.
36:35The construction of the great pyramids that you see in the temples and the carving of those stele was all done with human labor.
36:41And so it's extremely important to know what the capabilities are of this valley in terms of supporting large populations,
36:48of sustaining a population for those kinds of activities.
36:51Today, the Copan Valley supports about 25,000 people, almost as many as lived here just before the Maya collapse.
37:03And these people are sustained by maize or corn, as were the Maya.
37:07By investigating how modern farmers earn a livelihood, Bill Sanders hopes to understand the capacity of the valley to support ancient populations as well.
37:19What he's telling me is that he's had this land nine years and before that it was in cattle pasture, just like most of this land around here.
37:36And he got something like 1,200 kilos and that yield is now only one third.
37:40This year he expects to get one third of that.
37:43It's not an isolated incident. By interviewing dozens of farmers, Sanders learnt that crop yields are declining throughout the valley.
37:51This is because the fallow or resting period that soils need to regain their fertility has been cut short.
38:01This is exactly what Sanders thinks may have happened in the past.
38:06When a subsistence farming population come into an area like this as pioneers,
38:12what they usually do is practice a long fallow system of farming.
38:16They'll crop land for a year or two and then they'll let it go back to high forest again.
38:21Then what happens as population increases, you have to reduce the fallow because there just isn't enough land to let it all go back into high forest.
38:27And that process at the end can result in a landscape in which the land is cultivated, every piece of land is cultivated every year or every other year.
38:36And this is what's happened here.
38:38All of the evidence we have from the archaeological survey of the valley shows that at the peak of Copan in the 8th century AD,
38:47that the ratio of people to land must have been about as high as it is today in this area, possibly even higher.
38:52And so the Maya must have been cropping the land every other year or perhaps even every year.
38:58And that just cannot be sustained on a long term basis.
39:03As the ancient population grew, so did the demand for land.
39:07Sanders and Webster believe that Maya farmers like these today were forced to cultivate even the steepest slopes, causing disastrous soil erosion.
39:15But could they find archaeological evidence to support their theory?
39:22The results of over-farming the hillsides can be seen here in an excavation on the valley floor.
39:30While digging this mound in a modern cornfield, David Webster discovered a Maya dwelling buried by tons of topsoil.
39:37We finally found the original floor down here, which the Maya built, and this wall sits right on top of it.
39:46We unexpectedly found this other little building here that they erected right next to it, creating this little corridor about 80 centimeters wide.
39:54But what's really interesting are the deposits in this corridor.
39:57Down here you've got about 15 or 20 centimeters of real garbage, sherds and obsidian, the kind of material that pre-industrial people always discard near their houses.
40:08On top of it is about 70 centimeters of this eroded brown soil from the hillsides up to the north,
40:15which eventually covered this little platform.
40:18But we know the Maya were still here because they placed this big slab partly on top of the little platform, but partly on top of the level of eroded soil that came across like this.
40:29Right after that, the whole north wall of this big elite structure fell right down, creating all this collapsed debris, a couple meters of it here, as you can see.
40:38But even that was eventually buried by even more erosion from those hillsides.
40:42So what we know is that while the Maya were living here, they caused a lot of erosion.
40:47And after this building collapsed, it continued so that enough soil was coming off those hillsides up there to make it probably impossible for farmers to get any kind of decent crop at all.
40:59Evidence from past and present converge to suggest that the Maya collapsed because they could no longer grow enough food.
41:06To confirm this theory, the archaeologists sought evidence of malnutrition in the Maya.
41:17In 1989, Stephen Whittington was excavating a small settlement site a few miles from the Copanacropolis.
41:24This site was occupied between about 650 and 900 AD. In other words, it straddled the time of the peak and entered the first period of the collapse of Copan.
41:37About two weeks ago, we put in a pit and we immediately found a stairway made of very nicely cut stones.
41:44That indicates that somebody important lived on top and the structure itself had some important function for the entire site.
41:51One strange thing about the stairway was that we discovered the three of the stones right in the center had moved out of place for some reason, as if they had fallen into a hole.
42:02This hole is a Maya grave.
42:08The burial site contains no jade or gold, but for the archaeologists, it holds a greater treasure.
42:25These are the remains of the people of Copan. They reveal much about life in the ancient city.
42:31Skeletons are one of our best sources of information about the past that we can recover archaeologically.
42:42Rebecca Storey specializes in reading the bones for clues to ancient diet and health.
42:47This is a young Maya woman. I know she's of high rank because she has the artificial deformation of the skull.
42:56Notice how it's flattened here in the front and in the back.
42:59Her head was deliberately bound, probably by her parents, to give her this kind of a profile.
43:04Besides the head flattening, though, she also has the nice dental mutilation, this very nice elaborate kind of cross pattern,
43:11done to her to also indicate her high rank.
43:15Now, the importance of this skull is not so much the evidence of high rank, but the evidence instead of stress.
43:23Here on the back, I have the remains of what was iron deficiency anemia.
43:28The bone becomes very porous and spongy as the body reacts to the malnutrition in the diet.
43:34Now, she was lucky it healed.
43:36I have several skeletons at Copan, however, that did not survive the episode.
43:40And here you can see the sponginess and porosity of the active lesion of the anemia.
43:46This individual unfortunately died before it could heal.
43:51Anemia can be seen in over 80% of Storey's skeletons, most of whom were nobles.
43:57Commoners fared even worse.
43:58We think that the best explanation for the collapse here at Copan is that there was a steady growth of population,
44:09increased intensification of agriculture.
44:12This caused disastrous effects on this landscape,
44:16and also the problems of adapting to that situation caused severe nutritional stress and disease on the human population,
44:25all leading to a disappearance of the population by around 1200 AD.
44:30All animals, including humans, increase their numbers to fill the environments they inhabit.
44:38800 years ago, the Maya overreached their capacity to gain sustenance from this land, and they disappeared.
44:47A process that required more than a thousand years in the past is now occurring in only a few generations.
44:58Today, once again, about 25,000 people live in the Copan Valley.
45:03There is an ancient saying throughout most of Latin America,
45:09sembramos para cosechar, which means, we sow that we may reap.
45:13It's a metaphor that explains the dramatic population growth common to most of the Third World's farmlands.
45:28Here, the impulse to have children fits a traditional logic.
45:32They provide the labor essential for survival in these rural villages.
45:35But these children, unlike their Maya predecessors, are in no immediate danger of starvation.
45:48Today, food is imported into the valley.
45:52Fertilizer nourishes fields that now are farmed without ceasing.
45:59And modern healthcare staves off disease.
46:05But only for a time.
46:09After the classic Maya abandoned this valley around 1200 AD,
46:14it wasn't reoccupied until early in the 19th century.
46:18Since then, the population has steadily increased to reach a point today approximately the same as it was just before the classic Maya collapse.
46:26The difference is that in the 20th century, it has been increasing at a rate four times as fast.
46:33And what this means is that within 23 years, the population will be double what it was at the classic Maya peak.
46:40Modern hunter and farmers make short-term contingent decisions.
46:44They do what they have to do to keep themselves and their families going.
46:47Now, the ancient Maya went from one short-term decision to another and ultimately destroyed their basic resource, which was, of course, land.
46:58Today, we're doing what humans have always done.
47:03We're making immediate decisions without regard to their ultimate consequences.
47:08Mexico City is one of the largest and fastest growing cities in the world.
47:14Its population doubles every 30 years.
47:17The human avalanche comes from the countryside.
47:19Illegal settlements of squatters on the outskirts of the city are bursting at the seams.
47:28To discourage the growth of these illegal communities, the Mexican government is encouraging settlement of the rainforest.
47:35In a vast area of Latin America, these modern-day pioneers are stripping away the rainforests at an alarming rate, 50 acres a day.
47:43Astonished American astronauts observed the result as they orbited high above the Earth.
47:53This is a view of the Yucatan Peninsula.
47:59Enlargement of one section of the photo provides startling evidence of Mexico's resettlement project.
48:06The sharp line is the border between Mexico and Guatemala.
48:10It has been etched on the very surface of the Earth by colonists cutting down the rainforest to make agricultural fields.
48:20Today, as in the past, advances in technology provide a new level of living for everyone.
48:26But with this progress, the potential for destruction has been magnified 1,000 times.
48:31In the world today, we have two blocks of nations, both headed for an ecological disaster of worldwide proportions.
48:41On the one hand, we have Western industrial civilizations with expanding economies who monopolize the wealth of the world,
48:47who are polluting the air and water, possibly even destroying the atmosphere, and consuming the very energy that sustains them.
48:56We have another block, the agrarian nations, characterized by high fertility, but also today low mortality, which means that they are increasing at an unprecedented and exponential rate.
49:06It is very doubtful that improvements in agricultural production can keep pace with that rate of growth.
49:16Of all the species on Earth, only mankind can learn from the past.
49:22What lessons for the future will come from our voyage through time?
49:33Will our new perspective on planet Earth convince us at last that all human societies and all human actions are forever intertwined?
49:42The view from above is disquieting. Stains from topsoil bleeding from the hills of Madagascar color the Indian Ocean.
49:53Plumes of smoke billow from man-made fires in Mozambique.
50:01Perhaps it is just the scale of our impact on Earth that has changed.
50:05Perhaps we have yet to learn that the mistakes of our ancestors do echo into the future.
50:10And if we listen closely, we may know they are speaking to us all.
50:40Amen.
50:41Amen.
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