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tonight, imagine the unimaginable. everywhere, nature becomesthe enemy of all humanity and everything changes. it may have happened 1,500 years ago. what could have so violentlychanged our world? uncover the secrets of the dead. catastrophe! (15 may 2001)season one, episode one - part one secrets of the dead was made possible by the corporation for public broadcasting

and by contributions to your pbs station from: narrator:1,500 years ago, something extreme happened to the world's climate. something that must have terrified those who witnessed it. the sun began to go dark. rain poured red, as if tinted by blood. clouds of dust enveloped the earth. cold gripped the land for two years.

then came drought... famine... plague... death. whole cities were wiped out. civilizations crumbled. there is evidence of a catastrophe. a catastrophe whose consequencesaffected the entire world and may have changedthe course of human history.

man:the mid-sixth century catastrophe was the most important date in the history of the past 2,000 years. it really did laythe foundations of the world we live in today. narrator [roy scheider}:from the attic of his unassuming suburban home david keys, a writer on history and archaeology has developed a controversial theory about an ancient catastrophe.

for five years, he has investigated, consulted with more than40 scientists and scholars-- astronomers, physicists,climatologists and historians-- experts on cosmic collisions, volcanoes, epidemics and ancient wars. from mexico to byzantium, from africa to indonesia, he has scoured the annals and chronicles of the sixth and seventh centuries a.d.

the result is a book that tells the story ofa catastrophic climatic event buried in the heart of the dark ages. an event keys believes totally altered the course of world history. the mystery that has consumedhim first presented itself at a conference on archaeology in 1994. keys:one particular talk really amazed me. it was a lecture given bya dendrochronologist,

an expert in tree rings, called mike baillie. and he was giving a lecture about how all the tree rings in the world really went haywire somewhere inthe middle of the sixth century. narrator:mike baillie is an archaeologistand palaeoecologist at queens university in belfast, ireland. he has a special interest in volcano and comet induced environmental change and uses tree rings to tracksignificant climatic variations.

annual tree ring growth was discovered by the ancient greeks. and as far back as leonardo da vinci, the connection between climateand ring growth has been known. trees have always had the potential to become silent witnesses to thousands of years of climatic change. every year, trees put out a newlayer of growth within the bark. these layers show up as rings.

each ring varies in width. a wide ring indicatesfavorable growing conditions a narrow ring, harder times. the pattern of wideand narrow rings is distinctive. mike baillie and his colleaguesdeveloped a high-tech method to tap into this resource. by feeding specific treemeasurements into a database each ring sequence could be matched with rings of previously felledtrees and precisely dated.

a bigger climatic picture began to emerge. over the last 30 years in northern europe - a variety of people, a variety of laboratories - have set out and worked backfrom known felling dates. taking you back through longring records of living trees and then overlapping to patterns from historic buildings.for example: fitting together these sort oflong ring patterns going back hundreds and,eventually, thousands of years.

narratorr:it is by painstakingly analyzing and overlapping the patterns of older and older trees that a complete, unbroken recordof tree ring widths is built up. baillie:so you've got this sample with its very clearcharacter change just here. when we processed another samplefrom the same building, we could see that it came originally from the same parent tree and you could extend the patternback from the first sample

right back throughto the beginning of this sample. narrator:many, many samples have to beanalyzed by a computer program to get the average width for every year. it took mike baillie 14 yearsto build up the complete data just for irish oaks. this tree record is now telling scientists what the weather was like every single year for the last seven amd one-half thousand years. baillie:if you think about that,

that's an astonishing position to be in. we can interrogate for any calendar year in the last thousands of years what trees thoughtof their growth conditions over a big geographical area. and that information simplydidn't exist before. but what we're interested in is why did this tree go narrow at this point and narrow again at this point.

what is the environmental information which is actually stored in the patterns? narrator:david keys wanted to see for himself the mysterious sixth-century event stored in mike baillie's tree rings. yeah, shuffle through here, david. narrator:it was ten years ago that baillie noticed his mid-sixth century a.d. oakrings went abnormally narrow. a sign that something very powerful

was slowing the trees' growth. baillie:539, 540, '41, '42--extremely narrow. narrator:and he has corroborating evidence from a colleague in finland. he sees a really abrupt dropin 536. a bit of a recovery in 537 and '38. and then it drops dramatically into 542. so you're beginning to see a pattern. narrator:the pattern was not justconfined to ireland and finland.

david keys began contacting other labs and found that almost everywhere he looked in the mid-sixth century, trees were showing unusual growth patterns indicative of cold conditions. foxtail pine rings from the sierra nevada mountains in california show that 535, 536 and 541 were three of the four worstyears in the past two millennia.

in chile, fitzroya trees recordthe greatest summer growth drop of the past 1,600 years,as do scots pines in sweden. in siberia, a 20-year declinein tree growth that began in the 530s was the most serious in the past 1,900 years. so, what happened to the trees? was it darkness, cold, natural pollution or drought? mike baillie looked for the answer in a microscopic examinationof a 536 a.d. oak ring.

he found evidence of drasticallyreduced summer growth. just for interest's sake, a colleague in germany sent me this photograph of one of his german oaks. the tree puts on a lineof these large spring vessels and it then puts on fine cell wood during the summer. then it goes dormant, thenit does again the next year. so each year's growth is from the beginningof one line of vessels

is the beginning of the next. and in this year, the year 536,the vessels are enormously small and they're also distributedright through the summer. it's widely reckoned that this phenomenon is due to frost damage. narrator:the evidence was adding up. the implication was of missed summers and long stretches of extremecold in the mid-sixth century. and mike bailliealso had archaeological evidence

from ireland to back up this theory. much of the wood that he hasdated came from crannogs-- wooden forts built over waterwhere people sought refuge during times of troubleand clan warfare. baillie took keysto the remains of one crannog in lough catherine, near belfast, to look at the submerged timbersthat once formed the outer wall. baillie:my first inkling thatthere was something going on came from timbers specificallyfrom sites like this.

narrator:the mid-sixth century marks the beginningof the construction of crannogs. baillie sees a strong connectionbetween the need for such forts and the deteriorating climate. baillie:when you look at the overallpicture there seems to be about a decade of really bad conditions starting in 536 and running oninto the mid-540s, at least. the implication from lots of bits of evidence is that it was extremely cold

and that this reduced sunlightand cold caused crop failures. so basically, people in an area like this would be forced back onto non-agricultural produce. they would be forced to fish. they would be forced to hunt. and that would puta lot of strain on a population, which was usedto having agricultural produce to see them through the winters,for example. so, i think things wouldhave been fairly bleak here.

narrator:keys was hooked-- not just by the tree ringevidence that it was cold but because peopleseemed to be suffering. his next step was to see whether there were any written historical accounts that described a climaticcatastrophe during that period. the mid-sixth century is the time of the dark ages in britain and little writing survives from that era.

but by far, the greatestcivilization of the time was the roman empire. rome had been sackeda hundred years earlier by huns and goths. now it was resurgent, with a new capital in constantinople. it was winning back territorythroughout the mediterranean. by contacting classical scholars, keys unearthed many highlysignificant roman accounts

of bizarre weather. one eyewitness, a syrian bishop,john of ephesus, describes the extraordinary events during the years 535 and 536 a.d. john (dramatized):there was a sign from the sun the like of which had never beenseen or reported before. the sun became dark and itsdarkness lasted for 18 months. each day it shone for about four hours and still this lightwas only a feeble shadow.

everyone declared that the sun would never recover its full light again. narrator:one of the consultants david keys contacted, mike whitby of warwick university, sees great significance in these records. whitby:historians of the sixth-century empire do not usually record climatic events unless they are something really stupendous. a natural event like a cometwill get mentioned.

now, in the 530s...the fact that john mentions a two-year dimming of the sun indicates that it was significant. john, writing in constantinople, mentions it. cassiodorus, writing in italy, he, too, refers to a dimming of the sun. cassiodorus (dramatized):we have had a spring without mildness and a summer without heat. the months which should havebeen maturing the crops

have been chilled by north winds. rain is denied andthe reaper fears new frosts. narrator:these accounts from the mediterranean and the middle eastwere extraordinary on their own. but what about the othercivilizations of that time? keys scoured recordsfrom north and south china, korea and japan. keys:and, as it turned out, there were out of, say,well over 30...sources,

there were around a dozenwhich actually refer directly to the darkened sun eventor to its consequences, to its immediate climatic consequences. narrator:in 540, the japanese great king wrote: "food is the basisof the empire. "yellow gold "and 10,000 strings of cashcannot cure hunger. "what availsa thousand boxes of pearls to him who is starving of cold?"

the nan-shi ancient chronicleof southern china records: "yellow dust rained down like snow. it could be scooped up in handfuls." keys:as the research continued, i began to realize more and more that this disaster had reallyenveloped the entire world, that it just wasn't just a few places but it was virtually everywhere. narrator:armed with historical evidenceof a global disaster,

keys turned back to scienceto look for a culprit. climatologists had only one explanation for such sudden, extreme globalcooling and visible darkening: a dense veil of dust, ash or acid thrown up into the atmosphere,blocking many of the sun's rays. only three suspects could havecaused such a phenomenon: a volcano... an asteroid... or a comet.

david keys tried to imaginewhat life would have been like for the people who witnessed the catastrophe. were they engulfed by permanent winter? how would they have explained why the sky was darkand their crops were failing? would there have been cluesto the cause of the disaster? at los alamos, the birthplaceof the atomic bomb, scientists have been studying all the possible atmospheric consequences

of nuclear strikes and cosmic collisions. keys turned here to examine the likelihood that the cause of thecatastrophe came from the sky. we certainly have plenty of evidence that the earth is struck repeatedly by asteroids large and small,comets large and small. but you have to havea big thing that hits the ground in order to have a climate effect. narrator:extra-terrestrial bodiescome in all shapes and sizes.

meteors are small rocks that roam space, occasionally hitting planets,usually causing little damage. asteroids are big meteors. when these objects hit theearth's surface they explode, churning up vast amountsof dust and debris. david keys turned toan astrophysicist to calculate how big an impact would have been needed to generate a climatic catastrophe lasting at least a decade.

man:so even thinner, then "l" is thelength of that scattering haze. yeah? and so what we can see is that thetotal number of particles in the atmosphere because this is one, then rho is aroundone over kappa "l." to cause a major climatic catastrophe that would last decades,we would need an impact by a rather large asteroid,say four kilometers across. narrator:it would take an even biggercomet to create the same effect.

comets consist mainly of gas and ice, which give them their distinctive tails as they move across the sky. because they are less dense,alan fitzsimmons has calculated that it would takea six kilometer-wide comet to affect our climate. his calculations are supportedby the 1994 impact on jupiter by the comet shoemaker-levy. fitzsimmons:we saw a lot of the models

and a lot of the calculationswe had made about an asteroid or cometstrike on the earth vindicated. we saw the huge plume of debris of both jupiter itselfand the vaporized comet rise up in a huge mushroom cloud 2,000 kilometers high abovethe atmosphere of the planet. and then we saw it crash down again covering an area the size of theearth in a fine layer of dust. significantly cooling the atmosphere

and the planet underneath. narrator:fitzsimmons describeshow spectacular such a crash might be on earth. fitzsimmons:when it was just over two days from impact, it would only be seen as a veryfaint star in the night sky. now, as it approached us,as it got closer and closer, we slowly see it brighten and grow larger until about 30 minutes before impact. it would be aboutthe brightest thing in the sky.

and by then, of course, we believe everyone would have noticed it but we wouldn't be able todo anything about it. now...the time it takesfor that asteroid to travel from the top of the earth's atmosphere until it reaches sea levelis only eight seconds. so we'd see this brilliant fireball. all the time, of course, making no sound because it's traveling about20 times the speed of sound.

the first sound we would hear would occur minutes after we seethe huge flash of light when the asteroidstrikes the earth's surface and is instantly vaporized in a gi...enormous fireball. narrator:could this disaster have happened without anyone noticing it? no civilization at the timerecords any such event. in addition, scientistshave found no evidence

of a crater left by an impactfrom the sixth century. i mean, that's just yesterdayin geologic time. there'd be a big crater,we'd know about it. certainly that happened 65 million years ago when the dinosaurs died. but i don't think it happenedin the sixth century. fitzsimmons:and to cause such a global catastrophe, such a crater would be at leastten kilometers large, possibly much larger

and...there's no such evidenceof any such crater on the surface of the earth today. narrator:but the lack of crater alone does not rule outa comet or asteroid strike. 70% of the earth is covered in water. could the impact have taken place in the ocean? if the asteroid landed in theocean, then the initial wave caused by the impact would be miles high. jones:there would have beenhumongous tidal waves.

big, huge tidal waves thatwould have swamped the coasts for over the margins ofwhatever ocean it struck. narrator:the waves would have traveled miles inland. again, no civilizationrecorded such an event. and scientists have not detectedany significant break in coastal plant life during that period. there did not appear to be any evidence that an asteroid or comet hadstruck the earth at this time. but could there be anotherextra-terrestrial explanation.

not a complete comet hitting the earth but one that had fragmented and scattered throughout the atmosphere. it's a theory tree ring specialist and former physicist mikebaillie suggested to david keys. baillie:well, the bombardment eventhas been classically defined as a large number of pieces of comet arriving in a short period of time and exploding in the atmosphere.

and the model for that is the 1908 tunguska impact over siberia, which was a single objectwhich probably caused about a 20 megaton equivalent sizeexplosion. narrator:the 1908 tunguska event was an example of an airburst explosion. a lightweight meteorhit the earth's atmosphere and exploded in the air. while the shock wave causedmassive local destruction,

there weren't enoughmicrofine particles released to affect global conditions. but mike baillie claims that awhole shower of cometary debris hitting in a tunguska-styleevent could affect the climate. baillie:if you have a large number of those, you're going to put a lot of material in the atmosphere and cause a dust veil. narrator:baillie even turns to mythologyto support his theory. he has analyzed the life and death

of one of the most famouslegends of all time and reached an intriguing conclusion. sixth-century britain was supposedly the time of king arthur,king of the celtic britons. all the many legends tell that arthur lived in the west of britain and that, as he grew old, his kingdom was reduced to a wasteland as the british fought offinvaders from europe.

curiously, even though the arthur stories were written hundreds of years later, many of them suggestedthat the date of arthur's death was 539 or 542 a.d., right in the middleof the climatic catastrophe. the legends tell of terrible blows that rained down from theheavens onto arthur's people. baillie believes that arthur's death couldtherefore be a symbol

of something that really did happen-- devastation by a comet as itshattered and crashed to earth. baillie:then you look at the mythology--you discover that arthur isn't just somebody witha nice suit of shining armor and somebody sitting around a round table. the origins of the storiesare in celtic mythology. narrator:the myths that baillie saysarthur is based on contain many referencesto sun gods with long arms rising in the western sky.

he thinks this can only bea reference to a comet and its characteristic tail. for him, the evidence clearlypoints towards the sky as the source of the catastrophe. but david keys still wants to explore the possibility of a cataclysmic volcanic eruption. there is one hostile area of the earth that could hold the crucial clue-- the polar ice caps.

for the past decade, multinational teams ofscientists have been extracting 1,000 meter deep columns of icefrom greenland in the north aad from the antarctic in the south. while not as comprehensive asthe information from tree rings, ice cores reveal yearly layers of fresh snow that provide a wealth of detailabout what was in the atmosphere at that time. man:the ice caps containsinformation on what happened

in the atmosphere like volcanic eruptions, asteroids coming in,how much dust was in the air. a lot of information. the chemistry of the oldatmosphere is in there and even the chemistry todayis changing in our atmosphere. if we combine this, we can have a record which we can compare with other records from the deep sea sediments,from tree rings, from lakes. but the fantastic thing about the ice caps is

that they are directly relatedto the atmosphere itself. narrator:professor hammer's team istesting a new greenland core from the 530s a.d. that has just arrivedat their laboratory. if pieces of a comet or asteroidhad exploded in the atmosphere, the team would expect to find traces of rare chemical elements like iridium. if there had been a massivevolcanic eruption, however, they would expect an excess of sulfuric acid,

the telltale signature of a volcano. the sulfates would have beenhurled into the atmosphere and scattered by the winds. they would have returnedto earth in rain and snow, then finally been storedat the poles in ice. hammer:and what we are going to do now is take a piece of ice out,around 535 after christ. we will have to clean ita little roughly here first. we will now bring it intothis setup here,

where it will becleaned in the ends and on all sides and then it will be cut by thesteel knife so that we are not touching the core. we have to remove quite a lot to be sure that we don't have any ice outside contamination. narrator:the cleaned core is slicedinto five-centimeter lengths. each length is then melted and analyzed.

they will be measured one at atime automatically from now on and the results will show up onthis computer as chromatograms. narrator:what will the ice reveal? cometary debris or volcanic sulfates? siggaard-andersen:yeah, i can see the sulfate peakis increasing when i go to the next sample. that must be...come fromsulfuric acid in the atmosphere and that's an indication that there has been a volcanic eruption.

narrator:apparently, it wasn't just any eruption. and this, what is important i'll show you here, is the sulfuric acid and actually these hugeamounts of sulfate here, lasting several years and clearly higher than anythingelse in this part of the record corresponds exactly to this, around 535. so there's no doubt there is a major eruption. narrator:the results from greenland's endgrip core

seem conclusive to professor hammer-- lots of sulfates and no cometary debris. but for the eruption to havehad worldwide consequences more evidence was needed. if you want a climatic...important major eruption, it must show up with a largesignal in both hemispheres. that is, you must see itin antarctic ice cores and you must see it in greenland. narrator:current information fromthe antarctic ice cores

is incomplete. but professor hammer has found some evidence that indicates a volcanic signalin the southern hemisphere. hammer:we have a volcanic signalwhich lasts several years. we have from an antarctic coresimilar evidence as in greenland. but not as good, not as well dated but indicating that this volcanic eruption could have taken place. narrator:there is evidence from both ends of the earth

of a sulfur spike, aroundthe mid-sixth century. to keys, this stronglyindicates the likelihood of a major volcanic eruption just at the time he's investigating. and while the idea of avolcano wreaking climatic havoc may seem far-fetched, it is far more likely than acatastrophic cosmic collision. keys:cosmic collisions areextremely, extremely rare. i mean, they only happen

once every many, many,many millions of years whereas volcanic eruptionsare occurring... i won't say all the time, but they're certainly happening. every few thousand years, you get a really major volcanic eruption. narrator:tree rings and ice cores now show that, every thousand years or so, massive climate downturns have occurred.

the mid-sixth century event issimply one of the most recent. in fact, what surprises volcanologists is how few volcanic eruptionsthere have been in the last hundred years. one of the amazing thingswhich people sometimes forget, even scientists, is that our century is oneof the most quiet centuries with respect to volcanism. narrator:other eras have seen muchmore volcanic activity

and much more ash in the skies. hammer:if you go back in time in19th century, in 17th century, 18th century, there's a lot of volcanoes. they come in lumps, say,20, 30 years, a lot of them. they even overlap inthe stratosphere, mixing up. narrator:volcanic dust creates spectacular sunsets, which may have influencedthe paintings of joseph turner in the 19th century.

hammer:and it's not speculationbut people do think that turner's paintings with his sunsets, it was not the taste of the artist to make them so red as they were but they were actually painted in a time when the real sunset looked like that. narrator:we live on this planetwith over 200 active volcanoes. they may have been quiet recently, but a really massive eruption

can turn the climate upside down. to create a dust veilthat envelopes the world, the eruption has to happennear the equator as only equatorial windscan spread dust over both hemispheres. but there are over 90 equatorial volcanoes. could david keys figure outwhich one caused the mayhem of the sixth century? (volcano erupting)

narrator:keys began to narrow the search for the source of the sixth-century eruption. he turned to ancient writings looking for mention of such an event. he focused on the area with the world's highest concentration of large tropical volcanoes. the volcanoes form an arcstraddling southeast asia and keys found what he waslooking for in nearby china.

keys:i, in great excitement, started looking to see whether there was any traceof anything happening in 535. and, in fact, in february 535,there's a record of a loud bang, a huge thunderous soundcoming from the southwest. and with this one, there was no mentionof lightning or anything. it was merely a rathersort of mysterious entry in which they only referred tothe sort of thunderous noise.

and interestingly,that points straight towards that indonesian areawhere all those volcanoes are. narrato:the sound must have been extraordinary if the chinese bothered to record it. but could the sound of a volcanic eruption have traveled 3,000 milesfrom indonesia to china? to answer that question, keys turned back to expertsat los alamos laboratory to explain the physicsof long range sound travel.

we know that near the volcano, the sudden explosive eruptionprovides a shock wave in the near field,and that propagates out, going out to thousands of miles. but as it propagates outyou lose the high frequencies-- the shock, very sudden sharpreports of the volcanoes-- and all you're left withare the low frequencies that we measure inwhat we call infrasound, which is generally belowten cycles per second.

the long range perception of that sound would be very low rumbling,much like very distant thunder. we're still talking about hearing it so you're down at the very low end, the very low end of the human response. and so it's going to be very lowbass sounds, rumbling thunder. narrator:the los alamos experts had saidit was possible. now, could keys find any writtenevidence from indonesia? unfortunately, very littlewriting survives from the area.

but once again, keys founda fascinating clue. housed in the royal palaceat solo in central java is a massive set of 95 manuscript volumes called "the book of kings." it records all of java's historyand was put together in 1869 by a royal courtier called rangawarsita. some is folklore and myth but scholars believe much is based on genuine oral and written history

handed down through the generations. woman:rangawarsita was known to have done extensive fieldwork, as it were, traveling all over the islandof java and into bali, where it is said that he picked up great cachesof palm leaf manuscripts. narrator:in one volume, rangawarsitadescribes an extraordinary event that took place around the middleof the first millennium.

javanese royal archivist prince puger reads from the original text. (reading in local language) translator:"a mighty thunder which was answered "by a furious shaking of the earth, "pitch darkness, "thunder and lightning. "and then came forth a furious gale "together with a hard rain,

"a deadly storm darkeningthe entire world. "in no time, there came a great flood. "when the water subsided, "it could be seenthat the island of java "had been split in two, thus creating the island of sumatra." narrator:had keys struck goldwith "the book of kongs?" geophysicists he consulted said the story accurately described

a major volcanic eruption that would have been difficult to invent. and the only major volcanoin the specific area between the islands of sumatra and java, indicated by rangawarsita,is the legendary krakatoa, the world's most notorious volcano. but could keys provethat krakatoa was the culprit? icelandic volcanologistprofessor haraldur siggurdson now joined the chase.

he had studied the volcano and knew that krakatoa'shistory hid details of an ancient eruption far bigger than anyrecorded in modern times. about five years ago, whenwe were doing research on the 1883 volcaniceruption of krakatoa, we discovered this depositof a major eruption and so we became veryinterested in this deposit. but at the time we didn'thave the time and resources

to study it in detail,so what we really want to do is ideally find charcoalwithin this layer, or charcoal immediately aboveand immediately below it, in order to give us a date of the event. narrator:to give professor siggurdsonthe opportunity to unlock the history of krakatoa and search for the tell-tale charcoal, the film's producers decided tosponsor an expedition to java. the goal, to test keys' theory

by dating krakatoa's major eruption. krakatoa is part of a group ofuninhabited rain forest islands lying west of javaand just south of the equator. in addition to the ancient eruption sigurdsson is attempting to date, krakatoa is also the scene of the most deadly volcaniceruption in recent times. well, krakatoa becamea notorious volcano in 1883, when the eruption killed 36,000 people,

mostly by tidal waves but also by hot ash cloudssweeping over the ocean and reaching the land and incinerating people on theshores around the sunda straits. it is a very difficult area for access. it's remote andthe conditions are harsh here. the environment is difficult. narrator:the lava fieldson the island of anak krakatoa will be the first stopfor sigurdsson and his team.

"anak" means child and this child was bornout of the 1883 eruption. in just over a century, it has grown intoa thousand foot high volcano. the lava, rock and ash it frequently spewscontinues to accumulate. anak is unpredictable and each year it becomes biggerand more dangerous. sigurdsson:the volcano erupted this morning.

a small vulcanian explosion,as we call it. it threw out a lot of blocks and ash and created a plume rising upinto the atmosphere. now, actually, when you get up to them these rocks arethe size of houses, and... five, six meters in diameter. and these were ejectedby the explosions of anak and they traveled throughthe air like a bomb, basically, and they fall to the ground.

and when they hit the groundthey create a crater. now, this is about as big as they come! this one must be two meters high and, what do you think, about fourmeters wide? yeah, i'd say so. that's a big bomb. yeah, beautiful crust though. hard to imagine this thing flyingthrough the air and landing here during an explosion.

plunking down and creating this crater thatit sits in. this one is a good onebecause you can hide behind it in an explosion and take shelter. let's hope they don'tland like this today. it would be very dangerous. narrator:anak krakatoa is a noisyand quarrelsome child. only two hours after the teamleft the island, anak let rip...

hurling rocks and lava onto the area where the scientists had just stood. from the safety of the sea, they gazed backon one of mother nature's most impressive fireworks displays. these pyrotechnics are part ofa cycle that has been going on for hundreds of thousands of years. krakatoa erupts, islands grow till eventuallythey blow themselves apart.

sigurdsson's task isto journey back into history, to try to discover when krakatoa's major eruptionshave occurred. for decades, scientists havethought that krakatoa contains a centuries-old secret. illustrations taken from a 1920sbook show a possible pattern. first, there was ancient krakatoa, which exploded, possibly around 535. leaving islands behind that

through a series of minor eruptions grew into the krakatoa of 1883. this in turn blew up, leading tothe krakatoa islands of today. sigurdsson's last survey of the islands seemed to confirm this idea. five years ago, he chartedthe ocean floor using sonar. the charts show outlinesof a caldera-- the giant crater left aftera massive volcanic explosion. there is a structureout here in the ocean,

a circular structure which ismuch larger in diameter. and it is possiblethat this buried feature-- circular feature that we seehere to the north and the east may in fact be a giganticancient caldera of krakatoa. well, we must beright on the edge here. narrator:can sigurdsson find the hard evidence to date the major eruptionof ancient krakatoa? he is looking for charcoal which is formed when hot lavainstantly carbonizes trees.

for precise carbon dating, sigurdsson must find charcoalfrom the major eruption layer. failing that, he can narrowthe margin by finding charcoal in the layers above and below. wow, it's a vertical drop. narrator:still, no easy task. yeah, it looks like okay all the way. sigurdsson:i'm right in the middle of this major pyroclastic deposit

that was formed by a verylarge eruption of krakatoa. now, this is very likelyto be the deposit that was created by a eruption, possibly in the sixth century a.d. and this is the one i'd reallylike to get some charcoal from, so we can date this very important event. now, we'd be very lucky to find charcoal but i'm going to keepdigging around here a little bit and see what we got.

narrator:the material in the volcanicdebris layers left by krakatoa spans hundreds of thousands of years. and there is very littlecharcoal to be found. so each precious sample hasthe potential to narrow down the date of the major eruption. sigurdsson:often it's extremely difficultto find charcoal. you might think that therewould be a lot of burnt wood or carbonized trees here becauseit's a tropical environment. but many volcanoes are barren

because there's so much activitythat vegetation and the forest doesn't really get established. we've had a lot of problemwith finding charcoal in this particular deposit but we must keep in mind thatthey're only small pieces of the island sticking up above sea level so, we have a very small area to prospect. narrator:during the two weeks he was in krakatoa, professor sigurdsson was only able to find

ten charcoal samples. he found none big enough to carbon date from the major eruption layer. however, he did collect good samples from the layer immediately above it and from a layer a few levels below. the samples will now be dated to see whether the major eruption could have occurred in 535.

if not, it is highly unlikelykrakatoa is the culprit and david keys will haveto rethink his theory. six weeks later,the carbon dating is complete. professor sigurdsson faxes the results and his analysis to david keys. yeah! man:so, what's his assessment of it? it's really good news. narrator:the data shows that the layer

immediately above the major eruption dates from 1215 a.d. carbon from several layers belowis from 6600 b.c. back in his office, sigurdsson was able to make a deduction. well, if we look at thisin detail over here then we have this picture. we have 1215 a.d. right on top here in this deposit.

then we have the major eruption... deposit right underneath it. and then we have about five layers... and then, down here, we have the charcoalthat we dated as 6600 b.c. so, in here we have quitea period of activity and development of the volcano-- possibly several thousand years. now, that leads us to think

that the event is much closerto 1215 a.d. as opposed to 6600. that span still covers the 535 a.d. event, so it doesn't rule it out, at all. in fact, i think as a result of this, we are focusing more and morein on that time frame. he thinks that the lead period, the lead option, if you like, for when the major eruption thatwe're talking about took place was the first millennium a.d.

so, although technically it can be anythingbetween 6600 b.c. and 1300 a.d., all the other pieces of evidencethat he's got suggest that it's actually... we can narrow that down to the period, let's say, 0 to 1000. now, 535 is marvelously rightin the middle of that window. so, i think that it's looking good. narrator:david keys' years ofdetective work suggest to him

that there is overwhelming evidence of a massive volcanic eruptionaround 535 a.d. while some scientists believethere is not enough evidence to point a finger at krakatoa, others feel keys' hypothesisis not unreasonable. if krakatoa was the causeof the climatic catastrophe, it had to have beena spectacular explosion. such a cataclysmic eruption would have spewed ash and sulfur dioxide

high into the atmosphere, enshrouding the earth in twilight, causing global chaos and changing the course of human history. tonight, a global natural disaster... there's evidence one happened 1,500 years ago. but what did it meanfor those who lived then? did nature's fury bring empires to their knees and forever change civilization?

uncover "the secrets of the dead" catastrophe! (15 may 2001)season one, episode one - part two narrator [roy scheider]:535 a.d. has come and gone. the world has been hit by a catastrophe. now comes bizarre weather-- the sun is darkened, skies are turbulent, rain is red and snow falls yellow. there is frost and famine. seasons are blurred.

in some places, great droughtdestroys the land. in others, floods bring chaos. the world will never be the same. narrator:the theory belongs to david keys. with dogged detective work he has pieced together the storyof an ancient catastrophe. by bringing together evidence from contemporary eyewitnessaccounts and tree rings, he has developed a pictureof a lethal climate change

that began in the year 535 a.d.and affected most of the world for the next 10 to 20 years. he found three possible causes for the huge amountof dust, ash and water vapor that must have been hurledinto the atmosphere to block out the sun: a comet... or a volcano. the presence of sulfuric acid

in arctic and antarcticice cores from that period has pointed the finger ata massive volcanic eruption. but where did it occur? from chinese and javaneserecords, keys has deduced that the culprit could have been the world's most notoriousvolcano--krakatoa. volcanologist professor haraldursiggurdson took up the chase. he already knew that at somepoint in the distant past there had been a massiveeruption at krakatoa

that had left a huge depositof dust and ash. the goal of this trip wasto dig up charcoal, to carbon date the eruption, buthe was only able to find samples from the levels above and belowthe major eruption layer. the samples, while not as accurate as keys would have liked, did indicate that the gigantic eruptioncould have occurred during the first millennium. but for krakatoa to have been the cause

of the climatic catastrophe, it must have been a spectacular event. man:the amount of power generated by this eruptionwould have been equivalent to around 2,000 millionhiroshima-sized nuclear bombs. the eruption of this ancient krakatoa is something mankind has never witnessed. perhaps tens, hundreds of times larger than any volcano that's ever been witnessed.

narrator:david keys asked ken wohletz,an expert on krakatoa, to feed all the available data about the sixth-century climatechange into a super computer to simulate howthe explosion began to unfold. i will start the simulation and will show several phasesof the eruption. narrator:wohletz placed the eruptionin the sunda straits between java and sumatra. by combining tree ring and ice core data

with eyewitness accountsof the dimming of the sun, it is possible to estimatehow much material might have been thrown upinto the earth's atmosphere. with that figure, it is possible to calculate the scale and power of the explosion and its associated after effects. wohletz's simulation was used to model krakatoa's 535 a.d. big bang. keys:a giant, red-hot fountain of molten rock

would have towered over the countryside. a second crack let sea water in, creating a 30 mile-high fountain of magma. up to a thousand miles away, ash would have rained downon forests and fields. the towering clouds of steamand gas and ash pierced and shot upwards. and at times when it seemedit could go no higher, it would continue to go high,

eventually to the point whereit started to block out the sun in all directions and this gray-white cloud would then seem to sort of movelaterally across the sky like a mushroom cloud. keys:in a way, it would have beena sort of natural equivalent of a nuclear winter. narrator:the effects would have beenglobal and devastating. wohletz has seen evidenceof similar major eruptions farther back in history.

one remnant is a dormant volcano near his lab high in the hills of new mexico. the 22 kilometer-wide calderaat valle grande, new mexico last exploded a million years ago. ash from here landed as far away as louisiana. using the remains of valle grande, wohletz showed howhigh-flying volcanic emissions can travel great distances. this is ultra-fine volcanic ash

formed by phreatoplinian eruptions similar to what we thinkhappened in the sixth century at krakatoa. it's so fine... that even just a baby's breath of air will keep it suspended by minute turbulence. it will never fall to the earthas long as the air is moving, which, of course, it always doeshigh in the atmosphere. narrator:keys believes that in 535 a.d.,

similar microscopic particlesof ash and sulfur dioxide from krakatoa would have shrouded the sky in endless gray. temperatures would have dropped. without the full strength of the sun to heat and evaporate the oceans' surfaces. there would have been less moisture released into the atmosphere. as a result, there would have been

progressively less rainfall. as a result there were droughts and famines, very often at the end of major droughts you do get massive floods and that seems to have been what occurred. narrator:confident he understandsthe natural course of events, keys now delves intothe catastrophe's effects on human civilization. keys:i began to think to myself:

well, disruption as severe as this has got to have political consequences. it was reallythe long-term consequences that i was interested in, in isolating to see whether one big event can actually have a knock-on effect throughout history worldwide. narrator:the idea that nature and climatic change can alter history

is winning increasing respect from academics. in fact, evidence of the huge impact a volcanic eruption can have already exists from more recent times. less than 200 years ago, another indonesian volcano,tambora, exploded. man:the tambora eruption of 1815 produced a tremendous amountof sulfur dioxide that went up into the stratosphere.

in new england, there was a frost recorded every month during the summer,crop-killing frosts. there was starvation in partsof europe, social unrest. this led to...it triggered both the migrations out of germany into russia and triggered migration out of new england into the ohio valley and western united states. so it was a true social upheaval. and it's been referred to

as the last great subsistencecrisis in the western world and that was caused by a volcanic eruption. narrator:david keys wanted to prove that a more massive and longer-lasting eruption in 535 would have had an evengreater effect on world history. he decided to examinea series of historical puzzles from tom sixth century a.d. he looked at events that, from contemporary writingsand archaeological evidence,

were known to have taken place but whose causes had never beenfully explained. the first was the spread of a terrible disease that brought the mighty roman empire to its knees. by 535, under the emperor justinian, the empire, now based in constantinople, was flourishing. it had recovered from theassaults of the huns and goths and had recaptured much ofits former territory and glory.

but in 542 a.d., something awful struck at theheart of the roman civilization. the horrors were documentedby the monk evagrius. evagrius (dramatized):with some people it began in the head, made the eyes bloody and the face swollen, descended to the throat andthen removed them from mankind. with others, there was a flowing of the bowels. narrator:evagrius was describing the first recorded outbreak of bubonic plague.

could the plague have been tiedto the climatic catastrophe? plague is a bacillus bacterium transmitted from infected rats to humans. the carrier is the humble fleathat feeds on rat's blood. man:this is a flea which has had a blood meal and there's no plague organisms in its gut and you can see that its stomach is quite full and everything's fine. if we look at, if we contrast this with a flea

which has taken up some of the bacillus. we can see that there's a blockage here and this is brought about by a reaction between the bacillus and the flea's gut. now, the result of this is, of course, that the flea can't feed properly. they become so ravenously hungry because they begin to starve,in effect, the more they eat... well, they can eat and eat and eat

and they don't satisfy their hunger because their gut is blocked. and so they will jumponto absolutely anything in the chance of getting a free meal. narrator:as the rats themselves die from the plague, the fleas jump to other animals,including humans, for blood. and then, as evagrius describes,the agony begins. evagrius:some came out in buboes,which gave rise to great fevers, and they would die two or three days later

with their mindsin the same state as those who had suffered nothing andwith their bodies still robust. others lost their senses before dying. narrator:keys found out from scientiststhat outbreaks of the plague are strongly related to changes in climate. and the sort of changes that followed the 535 event, in particular coolingand unpredictable rainfall, have a huge impacton the spread of the disease. temperatures affecthow the plague bacteria form

in the flea's gut. clark:well, plague epidemics are temperature related. what happens is that in the gut of the flea the fibrin clot only forms at temperatures below 25 degrees centigrade. above 25 degrees centigrade, the clot doesn't form and any bacillus is simplypassed out of the flea with the feces. narrator:so cooler temperatures allowthe bacteria to flourish.

and there is new scientific evidence that cooler temperaturesalso increase rat populations. in colorado, scientists are detailingthe climate/plague connection. they examined 30 years of climate records and plague infectionsin the american southwest. their work shows that coolweather and additional rainfall significantly increasedthe prevalence of the plague. now, this model only talksabout the american southwest

but the general principleswe believe are involved here would be that once that cycle begins, you're likely to see a dramaticincrease in rodent populations, and when that occurs, then you have a greatly increased likelihood that you'll see these plague outbreaks in the animal populations,and that's the time when it can spill overto the human population. narrator:that is exactly what happened in the southwest

in the early 1980s. cooler conditions swelled rat populations. could a similar increasehave occurred in 535 a.d.? and if so, where? in ancient times, the plague could have comefrom only two sources. well, according to oneof our contemporary sources, the church historian evagrius, the plague originated in ethiopia.

people have attempted to argue the plague may have comefrom china, from the orient. but if that were the case, one would have expected it to reach persia before it reached the roman empire. what we know both scientificallyand historically is that the great lakes areaof central africa is one of the oldest foci ofplague activities in the world and that it would appear

that the assertion of evagrius is correct. narrator:because central africa tends to be hot, the disease is kept at bay. but if the region was affected by the global cooling of 535 and 536, it may have become a lethalbreeding ground for the plague. from africa, via the trade routes, ships' rats and sailorscould easily bring the plague up the coast, first hittingthe port of alexandria in egypt,

then north to the heartof the roman empire. and human greed for one precious commodity would only accelerate that process. in the sixth century, there was an enormous trade in african ivory. hundreds of tons of ivory are being brought into the empire every year and being processed for luxury furniture. for luxury objects

which important magistrateswould give out as gifts. processed for diplomatic giftsthat the emperor could then use to impress his neighbors further to the north and further to the west. people who would never have seenan elephant in their lives. keys:and it was essentially the european and mediterraneangreed for ivory that brought the roof in. narrator:only seven years afterthe 535 climatic catastrophe,

the ivory trade allowed the plague to surge into constantinople. whitby:its impact was devastating. they had to dispose of over 10,000 bodies a day, week after week after week; throwing them into the sea off special boats, sticking them in the towers of the city wall, filling up cisterns, digging up orchards. sarris:soldiers were forced to dig mass graves

in which to cast the bodiesof those who had died. the impression is one of chaosand pandemonium. whitby:constantinople, europe's biggest city, stank for month after month after month. narrator:one writer recorded that when the number of deadreached a quarter of a million, constantinople officialssimply stopped counting. as people left the stricken city, they took the plague to towns,villages and farms

throughout the empire. untold millions perished. and mike whitby believesthe long-term implications were disastrous for the romans. whitby:the plague struck a mortal blow at the health of the empire. it also struck a mortal blow at the military vitality of the empire, partly by killing off potential recruits.

also affects the armies indirectly-- less tax from farming, from agriculture. less money into imperial coffers. less money to pay troops. less money to hire mercenariesto supplement the armies. keys:the plague delivereda heavy punch from the south to the roman empire. it caused mayhem in the empire,massively reduced population. it had all sorts of economic,military, social implications

but there was another punchwhich hit the empire, this time, really, from the east. (men shouting commands to horses) narrator:this second threat was brewingsome 3,000 miles away. the climatic event was havingan extraordinary effect on an extraordinary peopleand their livestock. in the isolated plainsof mongolia-- hundreds of miles north of china-- something strange was about to happen.

before 535 a.d., the overlords of the region were a tribe of violentbarbarian horsemen--the avars. chinese writers recordedtheir uncivilized way of life. these are foul-smelling barbarians. from their point of view, with outrageous habits. the avars never bathed,never washed their clothing. they cleaned their dishes byhaving the women lick them dry. all of which was simplyhorrifying to the chinese. narrator:but in one respect,

as both chinese chroniclesand archaeological finds show, the avars were years ahead of other cultures. finds from archaeological digs all over avar territories suggest that they were the most advancedhorsemen in the world. their style of riding, saddlesand mouth bits, are still in use by hungarian plainsmen today. and many believe that the avars almostcertainly invented the stirrup.

it was this large concentration of horses that gave them a military edge. the latest in the militarytechnology of that era. the horses also provided food and sustenance. the avars drank fermented mare'smilk, an alcoholic beverage. so horses were central to their existence narrator:but then, following 535 a.d., chinese records and tree-ring evidence from mongolia and siberia suggest

that the mongolian steppe wascrippled by cold and drought. these conditions may havelasted for more than a decade and may have severely weakened the avar nation. by 552 a.d., the avars were attacked by the turks, a people who livedin the surrounding highlands. they had previously been the avars' subjects but mysteriously, the once invincibleavar horsemen were crushed. up until now, the cause ofthis sudden reversal of power

has never been identified. but david keys had an idea. keys:so i was very puzzled by this and decided to try and find outwhat the mechanism was. i thought, well, maybe it's something to do with their economy. well, the avar economy wasa horse-based one. the turk economy wasa much more mixed one involving considerable numbers of cattle.

the question came to my mind,well, was there something about the way thata cattle economy works and a horse economy works,the difference between those that might shed some lighton the political events, on the demise of the avars? narrator:keys contacted john milneat the macaulay land use center in aberdeen, scotland. milne has made a detailed study of how different animals feed and survive.

yes, these horses here areactually highland ponies. but in terms of the sort ofsize, they're very similar to what i believe the avarhorses would have been like. they're quite similar to some of the-- at least in terms of size--in terms of the mongolian and kazhak horses that you see now. narrator:to understand the difference between horse-based and cattle-based economies, milne picks up some unexpected evidence.

milne:here you can see some horse dung and you can see that it's very fibrous, which demonstrates... and it's made up offairly large pieces of fiber which demonstrates that this has not beenwell digested by the horse. now, if you compared some cattle feces, you would see that it wasmuch more finely ground up and in fact much better digestedthan horse manure.

narrator:after the catastrophe,when the climate deteriorated and the vegetation grew sparseon the mongolian steppe, could the contrast in horses'and cows' digestive systems have made a vital differenceand put the avars at risk? milne:cows have a greater efficiencyto digest food. they also have the abilityto eat a wider range of different herbage types so that they can eat, forexample, very rank vegetation. in contrast, the horses areless capable of eating

rank, really poor qualityvegetation than cattle. and, in a drought situation, you would get eventually to the state where the horse was not ableto eat enough food and because it was not ableto digest it successfully, then it would not be able to survive. and so in those circumstances then the avars would be very vulnerable. i was absolutely amazed when i found

that, in fact, it was merely the differences between a cow's and a horse's stomach design that had probably had such a major effect on subsequent history. narrator:chinese chronicles record how in defeat at the hands of the turks, thousands of avars wereslaughtered or enslaved. their leader committed suicide. most of the surviving avars began

a 4,000-mile trek westwards. their journey was about to playa huge part in history. the avar refugee caravan cut across what is now northern kazakhstan, skirted the northern shoreof the caspian sea and into the fertile grasslands south of the carpathian mountains. the area that is now the balkans. as they traveled, the avars recovered.

their horse technology was still superior to anything they found on their route. once again they became a conquering people, driving all others before them. eventually they reachedthe fringes of the roman empire. whitby:they arrive in the late 550s as refugees. within a decade, their ruthless horsemanship, ruthless military ability hascome to dominate all the tribes, all the groups of slavs, huns, germans

living north of the danubeon the empire's frontiers. and having imposed their controlover these groups, the avars can then turn theirattention against the empire. the impact of the avarswas particularly devastating because when they capturedfortified cities, the fate of the inhabitantswas not pleasant. people would be impaled. if they were lucky, they could betaken off into captivity and exploited as avar serfs oras cannon fodder in avar armies.

narrator:the empire, already weakened by the plague. was constantly harassed by avar incursions. at one point, even constantinople was besieged. rather than take over,the avars opted for blackmail and extracted vast amountsof gold from the empire in return for peace. some of it can be seen today in museums. much of it is rumored to lie buried under the plains of hungary.

historians believethat over a 50-year period, the avars netted gold from the roman empire that would be worth $11 billion today. the avar impact combined with the plague and the economic problems thatensued destabilized the empire. and at the end of the day, it can all be traced back tothis climatic destabilization of the mid-sixth century which was triggeredby the volcanic eruption.

narrator:david keys believed a pattern was emerging that showed huge political consequences stemming from the catastrophe. by now, he had found falloutin europe and the east. he next turned to the americas to investigate an extraordinary coincidence of timing and another historical puzzle where a great city had fallenwithout explanation. in the early sixth century,

125,000 people lived in teotihuacan, in the central mexican plain. man:in 500 a.d., when this city reached its peak, it really was what is called a primate city. and by that i mean the second next-largest city is so far below it in size that really, you could almostsay there are no other cities. i mean, that's an overstatement,obviously-- there were cities of 10,000 people, 20,000.

but compared to the 125,000here, that was nothing. so it was the only huge, large city in the entire central mexican plateau. narrator:then, midway through the sixthcentury, shortly after 535 a.d., things began to go terribly wrong in teotihuacan. for the past 12 years, rebecca storey has beenpainstakingly studying skeletons of people who once livedin one of the city's suburbs called clahinga.

the bones provide a remarkable history of the population's health. well, the clahinga population has adults. it also has quite a few childrenand an awful lot of babies. narrator:storey began to notice thatin teotihuacan's later period, the population, andin particular, the babies suffered a severe decline in health. these kinds of infectionsthat show up on the bone are long-lasting bacterial infections

and they're very common on the children. now, babies shouldn't haveinfections like this. normally they should be born with relatively goodimmunological protection from their parents, their mother. but in the case of clahinga,we find lots of babies with already infectious reactions indicating that the healthof the mothers was so poor that the children are getting sick as well.

the problem with the very late population around the sixth century is that overwhelmingly, it is babies, children and individuals under the age of 25. they should not be dying at that proportion. so they start to become 70% of my sample, rather than the much lower40% or 45% that they were in the earlier period. it is a population that is in great trouble

and is probably collapsing. narrator:new scientific evidence suggeststhat the city's decline occurred around the middle to late sixth century-- 150 years earlier than previously thought. for david keys, this re-dating is a breakthrough. now, in fact, one can see that teotihuacan's fall really comes straight on theheels of the climatic disaster. and i think that there'sa very, very high chance the two are connected.

narrator:there are no existing tree rings or other evidence from mexico itself to show whether there wasa significant climate change. however, lake depositsin the nearby yucatan peninsula show a possible 30-year drought starting in the mid sixth century. tree ring evidence from california shows a dramatic reduction in tree growth from the late 530s onwards.

a study of river levels in colombia shows that the mid to late sixth century seemed to be the driest period in the last 3,000 years. the indications throughout the americas, combined with rebecca storey'sfindings of malnutrition, suggest to david keysthat teotihuacan was gripped by a long-lasting drought that devastated the city's food supply. a drought keys believes was directly linked

to the climatic catastrophe. when something happens to the food supply... well, that makes peoplemore subject to getting ill because they're not getting enough food. then this is a very dry environment. water had to always have to havebeen a very important thing and without water you havegreat sanitation problems. sanitation would then leadto lots of diseases circulating through the people and causingmortality and ill health.

and that affects the productivity of a city. a city's not productive when its people are sick and that becomes one of the things that then they say: "well, no, we don't want to goto teotihuacan anymore because it's not a good place to be." narrator:according to the latest research, teotihuacan was finally destroyed when the people rose up against their leader,

smashing the palaces and setting the city's biggest temple ablaze. somebody went in there andset fire to all the roof beams and caused the ceiling and roof to collapse, bringing down the upper wallsand formed a big mound of debris. and that's what happened all up and down the main street of the city. maybe they decided that elite class that was makingdemands on them,

was asking too much, that the priests who weresupposedly bringing the rain and making the springs flowwere no longer successful because the spring flow was dropping and rains were diminishing. and they lost confidence maybein the priestly class as well. what appears to happen is thatyou've got a destabilization, perhaps some religiousand political changes followed by revolution of some sort

and the collapse of the city. in a way, similar to events in europe indeed, in the way that constantinople and the roman empire was affected. 535 disturbs the status quo and allows history to reformitself all over the world. it really is the interfacebetween the ancient world and the world we live in today. narrator:in central mexico, it took 300 years

for a new civilization to establish itself. throughout the sixth century,similar stories were unfolding. ancient civilizations crumbled,others were just beginning. and according to david keys,the emergence of the new-- including the birth of england-- can also be linked to the catastrophe. britain in the mid sixthcentury, the dark ages. the romans had lefta hundred years earlier. in the west of the island,

native british tribes--the celts-- fought to stem the tideof anglo-saxon invasion. according to legend, it was the time of the death of king arthur, when his country turned to a wasteland. man:as he rode thus throughthe lands, he found trees down and grain destroyedand all things laid waste as if lightning had struck in each place. he found half the people in the villages dead.

the earth no longer produced when cultivated. from that time on, no wheat or other grain grew there. no tree bore fruit and very fewfish were found in the sea. for this reason the two kingdomswere called the wasteland. narrator:but could the wasteland of legend be a distant memory of the 535 catastrophe? what is certain from britishand irish annals is that the bubonic plague thathad devastated the roman empire finally reached britain around 547 a.d.

it arrived on roman ships thatwere still trading with britain. this was a significant event in the history of western britain and ireland. certainly as one goes through the annals, one can find many references to plagues. one of them is referredto as the "mortalitas magna" - "the great mortality." another one is the "mortalitas prima"-- "the first plague like this."

this does suggest something special. keys:they'd never experienced the plague before. it was a completely new horrorthat they knew nothing about. they wouldn't have understoodeven what was happening. suddenly people began to developthese terrible pustules underneath their armpits,in their groins and they would have diedin the most terrible agony. narrator:according to keys, the plague changed the political shape of britain.

at that time, britain was divided in two. in the west lived the native celtic britons. the east was occupiedby invaders from europe-- the angles and the saxons. east and west had very littlecontact with each other. the anglo-saxon peoples traded mainly with theirformer homelands of germany and scandinavia. the celtic britons still tradedwith the roman world.

this meant that the celts wereat far greater risk of catching the plagueas it arrived on roman ships. keys:so by the time you come intothe latter part of the century, the celtic west and centerhave been... have experienced a huge population reduction. there's a population vacuum and so anglo-saxon peoplesare able to move from the east. they're able to move westinto partially empty lands and england was born.

narrator:keys' theory is that england was formed because the healthy anglo-saxonswere able to defeat the plague-stricken britons. keys:one can see 535 as a watershed, where you see the forces coming into play which create such countriesas england, spain, france japan, the united china. narrator:now came the final and most controversial turn in david keys' theory.

could the catastrophe have been linked not just to the emergence of new nations but also to the birth ofa new world religion--islam? this is what is left todayof the marib dam in yemen at the southern tip of arabia. but at the beginning of the sixth century, yemen was the region's greatest power and it depended on the marib dam-- its greatest engineering feat.

the marib was huge--2,000 feet long, feeding into hundreds of miles of canals. but within a few years of the 535 event, climatic chaos hit the region--first drought and then a succession of storms and flash floods that weakened the dam. the constant attempts to repair the dam are recorded on contemporary inscriptions. man:what we're looking at isone of the great inscriptions

that was put up on the facade of the dam, really commemoratingthe rebuilding of the dam, the repair of the dam,in this case in the year 542. and it's a long inscription describing all the various people who came and contributed to this. and we can pick out right inthe center here, the cartouche-- the symbol of the rulerof the kingdom at that stage, one abraha.

and there are a whole seriesof these inscriptions for about 200 or 300 years,and then they stop, which is very indicative of exactly what the arabicsources are telling us-- that there was a periodwhen this dam was broken and was not repaired again. narrator:the marib dam was ultimately abandoned and its ruin was the downfall of yemen. her people migrated to a new regional power base

that had emerged around medina and mecca, where back in 570 a.d., theprophet mohammed had been born. keys:it's in precisely that mecca/medina area that mohammed was based, and soit's really the growth of medina as an important political centerthat is so crucial in the early development of islam. narrator:keys contends that the climaticchaos weakened the marib and began the shift of power to medina, where mohammed's familywas already well established.

the prophet's familyor the prophet's ancestors had taken it upon themselvesreally to provide food, to import food into this area and provide food for the population. and this was one of theirclaims to fame and to status. narrator:mohammed's family's reputationfor social concern helped his ministry take root in a time of drought, famine and plague, which had by now made its way to arabia.

by the end of the sixth century, the people were crying outfor an end to their suffering. (praying in arabic) (prayers echoing) i think mohammed's message was attractive because this was a periodof upheaval and disturbance. one's got this whole apocalyptic atmosphere in the ancient world at that time. there's been war, there's been revolution.

the roman empire, which had really dominated the political scene for, what, 800 years, appeared to be tottering. kennedy:there is a lot of apocalypticliterature from this period. there are a lot of peoplesaying, this is terrible. the world's coming to an end. how do we interpret these disasters? what are they a sign of?and so on. keys:the political certainties of the world

were collapsing around everybody's ears. nobody seemed sure of the future. it was a very, very unsettled time to live. all these things can be traced back, to an extent, to the climatic chaoscaused by the eruption of 535 and they all feed intothe early evolution of islam. narrator:while some scientists remain skeptical about the cause and effects of the 535 event, keys' deductions provide a stern warning

about the global repercussions that could arise from a future climate-altering occurrence. keys:now, if a volcanic eruption in 535 could wreak all this havoc and draw the ancient world to a final close and really help laythe foundations of the world we live in today, what would happen if there wasanother massive eruption? narrator:keys' concern is more than just idle speculation.

while no one can predict exactly when a major eruption will happen, there are a handful of volcanicmonsters lurking underground. wohletz:the granddaddy of them all is believed to be yellowstone caldera in wyoming. this caldera is maybe twice the size of any known modern caldera and its eruptions, which haveoccurred not once, not twice but three times overthe last two million years,

indicate that it has devastatednorthern america several times. besides long valley caldera, there's a caldera in californiawhich is also heating up. the ground is shaking there. there's been a die-off ofthe forest by noxious gases, carbon dioxide coming out of the earth. the public is very concerned about that volcano. closer to home for some people would be the area around naples, italy.

sure, it's famous for vesuvius, which has erupted many times in the past and potentially will again in the future. there's also a calderajust on the north side of naples, underlying a metropolitan areaof campi flegrei and pozzuoli, where thousands of people liveand have lived for a long time. narrator:the last eruption in the campiflegrei complex was in 1538. at that time, 3,000 people were killed by the immediate explosion.

today, 400,000 people livewithin the same area. the whole complex is still active and capable of a major eruption. that would be a total disaster for italy, a major disaster for europe. and would no doubt haveworldwide climatic repercussions, which would have hugeimplications for agriculture, huge implications from a diseasepoint of view worldwide. and would no doubt havethe effect of destabilizing

all sorts of potentially unstable countries all over the world. it would change our climate. it would produce a change in thepattern of wet and dry cycles for vast portions of the earth. we're familiar with the el niã±o and la niã±a effects. this would be even a much greater perturbation, perhaps lowering the temperature, the global average temperatureseveral degrees or more.

the biggest effect for people anywhere is that it's going to disrupt the food supply and it's going to take years for the climate to either go back to normal or for people to change the crops that they use and the way that they plant them. man:there may not be food to importfrom other countries because they'll need it everybit as much or more than we will and if our agriculture has failed in some way

then there just wouldn't be enough to eat. i mean, that to me seems to bethe logic of the situation. now, in times past, you'reright, subsistence economies if they had low population densities, they could go to the seashore and live on shellfish. and, indeed, people sometimes did that under really stressful conditions. but you can't do that nowadays. there aren't enough shellfish to go round.

if we were confronted with a global event at any time in the future, it's not quite clear how we would cope. man:the whole infrastructure of civilization would collapse around us due to the huge environmentalcatastrophe that would happen because of the failing of crop production, the darkening of the skies. sigurdsson:communications would be taken out,

satellite communication. aircraft transport would beinterrupted severely for a long period. that type of event will occur in the future. baillie:well... people start to struggle for resources and basically that means warfare. in the modern world, it's not quite clearexactly what would happen.

you either sit and starve or you get out there and try and acquire food. there's not much alternativein a really stressful situation. keyes:one of the big lessons from 535,i think is, that we're not talking about a big bang and then the world changes. we're talking about a big bang and then it takes 100 to 150 years for the new reality to actually emerge.

what will happen in the future,of course, one doesn't know but i think that historians,economists, politicians should really pay rathermore attention, perhaps to the ability of natural forcesto change history than they do at the moment. find more answersto history's greatest mysteries at pbs.org. captioned by the caption centerwgbh educational foundation secrets of the deadwas made possible

by the corporationfor public broadcasting and by contributions to your pbs station from viewers like you.