NOVA investigates an intriguing idea on the origin of the Ice Age: namely, the Himalayas did it. According to the theory, the crash of continents that produced Mount Everest also produced a complicated chain of effects that has resulted in a drastically altered world climate.
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00:00Tonight, on NOVA, track to the top of the world on an expedition that's putting a bold
00:07new theory to the test. Hunt for clues in a chilling mystery.
00:12Will you ever be able to find enough fossils and date them well enough?
00:16Do the Himalayas hold the key to the origin of the Ice Age?
00:20Did these mountains rise up and forever change the world's weather?
00:25Science takes a stand at cracking the Ice Age.
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01:20The Corporation for Public Broadcasting and viewers like you.
01:25The Himalayas are one of nature's finest masterpieces.
01:51Rising five miles into the sky, they are the highest and steepest mountains in the world.
02:02The creation of this magnificent landscape is one of the most dramatic tales in the Earth's history.
02:11Now, scientists believe that these mountains could hold the answer to one of the Earth's
02:16oldest mysteries, the cause of the Ice Age.
02:27The Earth formed about four and a half billion years ago in a violent inferno of rock and gas.
02:37Since then, the climate has almost always been hot.
02:42For hundreds of millions of years at a time, most of the land was lush, tropical forest.
02:55During these extensive warm periods, no ice seems to have existed anywhere on the planet, even at the poles.
03:03Punctuating this long record, though, are several mysterious cold spells, or Ice Ages,
03:09when vast portions of the Earth froze.
03:19The last Ice Age, probably the most severe of them all, started about 40 million years ago.
03:26Around that time, as if the Earth's thermostat got turned down, temperatures gradually started falling.
03:41Eventually, it got so cold that immense icebergs cluttered the oceans.
03:48So much water was frozen solid that sea levels dropped about 400 feet.
04:00Ice sheets up to several miles deep covered much of the Earth's surface.
04:08In the Northern Hemisphere, the ice sheets were as thick as a mountain,
04:14In the Northern Hemisphere, those ice sheets have been growing and retreating in fairly regular cycles for the last two and a half million years.
04:28Eventually, ice crept as far south as modern-day Nebraska, Chicago, and New York.
04:36About 12,000 years ago, that ice sheet shrank away.
04:44Scientists think the changes in the Earth's orbit explain the repeated growth and retreat of these ice sheets.
04:57The greater mystery, though, is why it got so cold in the first place.
05:04What caused the long, slow cooling trend after it had been warm for so long?
05:14The Earth's climate has been warm for hundreds of millions of years.
05:21Then that Earth began to change. It began to get cooler, first slowly.
05:26By about 40 million years ago, there was ice in Antarctica and in Greenland.
05:31It got colder still, and then almost in the twinkling of an eye, huge ice sheets began to form, eventually reaching depths of well over a mile.
05:40Why did that happen?
05:44That question has baffled scientists for over a century.
05:55Answers to the Ice Age mystery have ranged from fluctuations in the sun's output
06:01to dust injected into the atmosphere by large volcanic eruptions.
06:07Even life itself, all the animals, plants and other organisms on Earth, is believed to help regulate temperature.
06:19Now, adding to that list, some scientists are proposing a geological explanation for the Ice Age.
06:27It is a controversial new idea that links changes in global climate to one of the Earth's most impressive geological features,
06:35the Himalayas.
06:40Even from space, these mountains stand out like a giant scar on the face of the planet.
06:49This is some of the most rugged and wrinkled terrain on Earth.
06:56To investigate whether the formation of these mountains somehow caused the Ice Age,
07:01an international team of scientists recently ventured to this remote corner of the world.
07:09The expedition began in the Himalayan city of Lhasa, the ancient capital of Tibet.
07:16Now controlled by China, Tibet lies just above India in the heart of Asia.
07:23On its southern edge are the Himalayas.
07:27To their north is the vast Tibetan Plateau, about one-third the size of the United States.
07:36Averaging more than 15,000 feet above sea level, the Tibetan Plateau is the highest terrain on the planet, the roof of the world.
07:46It is so remote that half the population of the plateau still pursue the traditional nomadic lifestyle of their ancestors.
07:59Scientists have long sought access to this region, but few have ever been admitted.
08:05Protected by the Himalayas, traditional Tibetan society always discouraged exploration by outsiders.
08:16Until recently, that society was organized around a Buddhist religious hierarchy whose customs had remained unchanged for centuries.
08:26All that came to an end in 1949, when China invaded Tibet.
08:36A few years later, the Dalai Lama, Tibet's traditional leader, fled across the mountains to India, fearing for his safety.
08:45As China tightened its grip, much of ancient Tibetan society was obliterated.
09:02This region is still severely restricted by the Chinese.
09:07The Tibetan Plateau remains virtually unexplored.
09:19Scientific expeditions to this part of the world have led to the discovery of the ancient Tibetan language.
09:27The Tibetan Plateau
09:33Scientific expeditions to this part of the world are rare and only for the hardy.
09:40This one, in search of clues to the start of the Ice Age, would take more than two weeks to traverse about a thousand miles of the rugged Tibetan Plateau.
09:51The Ice Age
09:55The air at this altitude of 15,000 feet is thin, and even in the summer, temperatures drop well below freezing at night.
10:04The scientists on this expedition included those who support the idea that the Himalayas caused the Ice Age, as well as some who are more skeptical.
10:21While the sights in this region are always magnificent, this team was here to do more than enjoy the scenery.
10:29For those who know how to read it, this landscape tells a story.
10:34It is the story of the birth of the Himalayas, and of what happens when continents collide.
10:43The surface of the Earth is divided into huge moving plates.
10:47These plates separate at massive volcanic ridges the size of mountains on the seafloor.
10:53Magma from deep inside the Earth wells up between these ridges, spreading outward and forming new crust.
11:02This process is known as seafloor spreading.
11:05It is happening all the time, and accounts for about 80% of the world's volcanic activity.
11:18The continents were originally in very different positions than they are today.
11:25The plates are constantly in motion, and India and Asia were headed toward each other on a collision course.
11:34150 million years ago, I would have been standing on the southern edge of the Asian continent,
11:40and far away to the south there would have been an ocean, the Tethys Ocean,
11:44stretching for thousands of kilometers, and on the other side of that ocean there was the Indian continent.
11:51Now plate tectonics dragged the Indian continent closer and closer towards the Asian continent.
11:58About 45 million years ago, India crashed head-on into Asia, but it didn't stop there.
12:04Since that time, it has moved 2,000 kilometers north, plowing up mountains in front.
12:11The most spectacular consequence of this collision between the Indian subcontinent and the Asian continent is the Himalaya.
12:33Here we can see strata, which originally would have been laid down horizontal,
12:38and now they've been deformed, they've been upturned, they've been folded,
12:42they've been totally scrunched about, showing the impact of that major collision.
12:48As it crashed into Asia, the upper layers of the northern edge of India were sheared off and stacked up over the collision zone,
12:56forming the Himalayan mountains.
13:00India is still pushing underneath the Himalayas at about 2 centimeters a year,
13:05and as a result, the Himalayas continue to rise.
13:11On the other side of the Himalayas, this collision created the Tibetan Plateau.
13:19Year by year, while India moved north, it squeezed Asia upwards.
13:24At the same time, some of India also got forced down underneath Asia.
13:30Over millions of years, these forces raised the land from sea level to its present height of 15,000 feet.
13:43But what does the creation of mountains and plateaus have to do with the Ice Age?
13:49The idea that the two might be related came from an unlikely source, the ocean.
13:56While leading a scientific expedition at sea,
14:00marine geologist Bill Rudiman unexpectedly became interested in Tibet.
14:07For me, it all started with a cruise in the North Atlantic,
14:10and we drilled through hundreds of meters of glacial material,
14:15and then suddenly you come to a point where there's no more glacial material.
14:20Rudiman was working aboard this ship,
14:24drilling long, thin cores of sediment out of the bottom of the ocean.
14:33Scientists used these cores to study the Earth's climatic history.
14:39Trapped within the cores are the fossilized shells of tiny creatures
14:43that lived in the water millions of years ago.
14:49These creatures used the elements in the ocean to build their shells.
14:54The makeup of the water changes with variations in climate,
14:59so the composition of their shells reflects the temperature of the time
15:04By comparing the shells from different layers in the ocean floor,
15:08scientists can tell when it was warmer and when it was colder,
15:12building a record of temperature.
15:17Rudiman had drilled down to the time before ice sheets crept onto North America.
15:22Now he found himself wondering why it had become so cold
15:26and why it was so hard to breathe.
15:30Now he found himself wondering why it had become so cold that these ice sheets could form.
15:36Comes a time about a year later when you have to, if you're co-chief,
15:40you have to write up a synthesis of your results.
15:43You list what you found and then you take a stab at what's going on to explain it.
15:52To do that, Rudiman began looking for other changes in the Earth
15:56that might have caused the climate to cool down.
15:59Coming into the literature at that point was evidence for uplift of Tibet.
16:04That's a big change because Tibet is a huge feature.
16:07So creating that over the last 40 million years,
16:10but creating a lot of it in the last 10 million years is a big change.
16:16But did the creation of the Himalayas and the Tibetan Plateau
16:20actually cause the Ice Age or was it just an unrelated coincidence?
16:26Rudiman decided to investigate.
16:29I was thinking that we might make a major contribution
16:33to solving the problem at the beginning of glaciation,
16:36partly because uplifted terrain gets cooler
16:39and partly because it turns the winds in such a way that,
16:42for instance, there's a more northerly flow into North America,
16:46into the area where the glaciers grow.
16:48So it was a reasonable assumption that it might help promote glaciation.
16:53Rudiman began by looking at the way wind blows across the region.
16:59The mountains and plateau interrupt its smooth flow, forcing it to the north.
17:06Over the rest of the northern hemisphere,
17:08this increases wiggles or meanders in the jet stream,
17:12the higher-level winds that blow west to east across the globe.
17:17In North America, this brings cooler air from the Arctic further south.
17:24Rudiman wondered if this influx of cold air caused the ice sheets to grow.
17:30When Bill came along with the idea that perhaps mountain uplift
17:34was changing the wind patterns in the planet
17:38in a way that would promote glaciation in high latitudes,
17:42bring cold Arctic air further south,
17:45this was an exciting idea to me.
17:49To help him figure this out,
17:51Rudiman turned to climatologist John Kutzbach.
17:56What I want you to think about is this is a continent,
18:00and this is the Indian Ocean.
18:03And if we had a low-lying continent of this form,
18:07you might get a very weak convection cell with rising air
18:12spreading out in the upper atmosphere,
18:14and then air coming in from the surrounding ocean,
18:18perhaps producing a little bit of rain along the edges of the continent.
18:22But it just wouldn't be a very exciting circulation
18:25because there's nothing on this continent to really focus the heating of the sunlight.
18:32If instead we place a high plateau on a continent such as this,
18:39all of a sudden the sunlight during the summertime
18:42has a real focal point for heating this high plateau.
18:46So you have very more active currents of air rising over this plateau,
18:51spreading out, sinking, and air literally rushing in towards the continent.
18:57In addition to the air coming in towards the continent,
19:00the spin of the earth makes the air more or less spiral in,
19:05air coming in off the Indian Ocean,
19:07spiraling in over the continent,
19:08banging into the Tibetan Plateau, being forced to ascend,
19:12producing violent thunderstorms along the face of the plateau.
19:24It's easy to understand if you've been in a mountainous climate
19:27that mountains affect the airflow and local thunderstorms.
19:31But what surprised us was that the effects extended far beyond the Tibetan Plateau itself.
19:37Looking at what might have happened at the time the Himalayas were created,
19:41Kutzbach used a computer to simulate weather patterns under three different conditions.
19:48First, with no elevation in the area.
19:52Second, with the Tibetan Plateau at half its present height.
19:57And third, with the plateau at today's elevation of more than 15,000 feet.
20:01We've got this box outline where the Himalayan Mountains and the Tibetan Plateau are,
20:07so you can have that for reference.
20:09Then the coloring on here shows the rainfall patterns in the summertime
20:14on a world like our present world, but without the Tibetan Plateau.
20:19And you see that there's just a little bit of rainfall here in Southeast Asia and over in Africa.
20:25Now, if we look at the Himalayan Mountains,
20:27in Southeast Asia and over in Africa,
20:31now if we advance this to our experiment with half mountains,
20:36you see that things are beginning to happen.
20:39The region of high rainfall has increased over all of Southeast Asia
20:44and spreading up onto the Tibetan Plateau.
20:48And then if we go to the full mountain simulation,
20:53there's even a more dramatic change,
20:54very heavy precipitation on the south and southeast corner of the Tibetan Plateau over Southeastern Asia
21:02and a very large dry area extending from the Middle East into the Mediterranean and North Africa.
21:13The computer model was remarkably accurate at predicting the climate patterns in the region today.
21:19It does give you a feeling of power, almost like playing God,
21:23to be able to say to the mountains, rise up.
21:26And so you crank up the height of the mountain from one experiment to another
21:30and then it's really exciting to sit back and say, oh, what have we done?
21:34What did these changes produce?
21:42What these changes produced was a stronger Asian monsoon system.
21:46Perhaps ten times stronger than without the mountains.
21:52The uplifted land blocks the flow of air from the Indian Ocean
21:56and the moisture in that air falls out as rain over Southeast Asia.
22:03The world's heaviest precipitation, as much as 400 inches of rain,
22:07falls on the southern slopes of the Himalayas.
22:10I remember, still with a sense of delight, sitting in my office
22:14and we took the results from the model
22:17and I came to just a very different realization
22:21as to how beautifully the uplift of Tibet,
22:26the Tibetan Plateau, the Indian Ocean,
22:30the mountains, the mountains, the mountains,
22:34as to how beautifully the uplift of Tibet
22:39changes the distribution of moisture,
22:42where it's wet, where it's dry,
22:45which season it's wet or dry in.
22:47And so it actually puts the deserts into the places deserts are
22:53and puts the rainforest in the areas that rainforests are.
22:57It doesn't explain everything on the face of the earth,
22:59but it has a major effect on the patterns of wet and dry climate and vegetation.
23:04Not just on the plateau, but well around the plateau, upstream and downstream.
23:13The computer model showed climate evolving over time
23:16as a result of changes in the elevation of the Tibetan Plateau.
23:20Now they needed to find hard evidence to prove it.
23:24Maureen Rameau, then a graduate student working with Bill Rudiman,
23:28helped with this search.
23:30At the same time they were doing the experiments,
23:31putting in the half plateau,
23:33taking out the plateau completely
23:35and seeing what changes in atmospheric circulation there were.
23:40At the same time they were doing that,
23:43we were doing this vast literature search
23:45of how climate had changed in the northern hemisphere
23:48over the time interval that the uplift was happening.
23:53Plants are reliable indicators of climate at the time and place they grow.
23:58Whether it is wet or dry, warm or cold.
24:07Scouring the records of previous scientific expeditions,
24:11Rameau and her colleagues traced changes in plant life
24:14during the millions of years that the Himalayas were forming.
24:18Some plant here said this place got drier
24:21and some plant here said that place got colder.
24:24It was just amazing how well all the predictions of the model matched.
24:36But the computer model of the climate of the Tibetan region
24:40had one major drawback.
24:45It revealed that Tibet's impact on air circulation
24:49was just not strong enough to produce the ice age.
24:54The results of the model ended up explaining
24:58a little bit of almost everything except what we were after.
25:01There was really a very small cooling of the Arctic area
25:04and the areas where ice sheets must grow.
25:08Just putting the plateau in the models
25:11didn't really cause any major global cooling.
25:14You couldn't explain why an Arctic ice sheet grew.
25:17So it seemed like there still was some other cause for global cooling.
25:21This was something I was always thinking about
25:24and that was the whole reason I went to graduate school.
25:26I wanted to study climate change
25:28and in particular why the northern hemisphere ice ages started.
25:32The main component of climate change
25:35is a mechanism called the greenhouse effect.
25:38The amount of carbon dioxide in the Earth's atmosphere
25:41controls its temperature.
25:43Carbon dioxide traps heat from the sun.
25:46If the level of carbon dioxide increases,
25:49more heat gets trapped and the temperature rises.
25:53If carbon dioxide decreases,
25:56more heat escapes and the temperature falls.
26:00But what controls the level of carbon dioxide in the atmosphere?
26:05Most carbon dioxide enters the atmosphere
26:08by volcanic activity and seafloor spreading.
26:12In the air,
26:13carbon dioxide combines with rainwater
26:16making a weak acid that erodes rock.
26:19This chemical reaction removes carbon dioxide from the atmosphere.
26:24The dissolved carbon then washes into the oceans
26:27where organisms use it to make their shells.
26:30When they die,
26:32they settle to the bottom,
26:34forming the ocean floor.
26:37As seafloor spreading occurs,
26:40sediments on the ocean floor
26:41get dragged down and heated,
26:43releasing carbon dioxide.
26:45Then the process,
26:47known as the carbon cycle,
26:49starts all over again.
26:52One of the first to investigate
26:54how the carbon cycle influences global temperature
26:57was geochemist Robert Berner.
27:00I've been working on the whole problem of carbon and sediments
27:03for a very long time, maybe 30 years.
27:05But actually doing modeling of the carbon cycle,
27:07we started thinking about the problem around 1980.
27:10It was just an amazing model.
27:12I read the paper many, many times.
27:14I thought it was just so neat
27:16to think about climate this way.
27:19According to this model,
27:21climate is largely controlled
27:23by how much carbon dioxide
27:25enters the atmosphere from seafloor spreading.
27:29If seafloor spreading speeds up,
27:32the Earth releases more carbon dioxide
27:34and the temperature rises.
27:36If seafloor spreading slows down,
27:38then less carbon dioxide enters the atmosphere
27:41and the temperature falls.
27:44The real benefit of studying these models
27:47is to evaluate the different processes
27:49that affect carbon dioxide,
27:51how we circulate carbon
27:53from one part of the surface of the Earth
27:56to another and to the depths of the Earth.
27:58And we can learn more about geological processes
28:01by studying the carbon cycle.
28:02As well as trying to get at
28:04the goal, of course,
28:06of trying to get at
28:08what controls carbon dioxide
28:10over geologic time.
28:12It was a model that explained
28:14long-term climate change
28:16over the last 100 million years
28:18as a function of CO2 in the atmosphere,
28:20greenhouse effect hypothesis.
28:22So we think perhaps
28:24there's some correlation
28:26between our calculations and climate
28:28in the sense that low CO2
28:30could have triggered glaciations
28:32bringing about a reduced
28:34greenhouse effect.
28:38But Maureen Rameau
28:40thought she saw inconsistencies
28:42in the model.
28:44One of the things about the model
28:46that didn't jive was that
28:48there seemed to be this mismatch
28:50between what the model predicted
28:52and what really happened
28:54in geologic history.
28:56The model did not accurately predict
28:58the cooling of the last 20 million years.
29:00Perhaps another factor
29:02was carbon dioxide in the atmosphere.
29:04Rameau thought the Himalayas
29:06might provide a clue.
29:08These mountains are just falling apart.
29:11The rocks that make up the Himalayas
29:13are constantly being eroded,
29:15both by geological forces
29:17and by chemical erosion.
29:19This occurs when carbon dioxide
29:21dissolved in rainwater
29:23makes an acid and reacts with rock.
29:25You can do two things to a rock.
29:27You can break it up
29:29and you can dissolve it.
29:31Ultimately what you're doing
29:33is taking CO2 out of the atmosphere.
29:35CO2 in the atmosphere
29:37dissolves in rainwater,
29:39makes a very dilute acid,
29:41and attacks, etches the rock.
29:45When it dissolves,
29:47bits the rock,
29:49the elements recombine
29:51to form new minerals.
29:53In the process,
29:55the CO2 that was in the atmosphere
29:57ultimately ends up in a carbonate rock.
29:58The rivers are the conveyor belt
30:00taking the carbon from the land
30:02to the ocean where it's effectively
30:04removed from the atmosphere.
30:10As the Himalayas grew,
30:12huge amounts of rock
30:14were exposed to the elements.
30:20The heavy monsoon rains
30:22combined with carbon dioxide in the air
30:24and eroded the rock.
30:29Could this process,
30:31called chemical weathering,
30:33take so much carbon dioxide
30:35out of the atmosphere
30:37that global temperatures
30:39would drop enough
30:41to trigger an ice age?
30:43Few scientists thought it could.
30:45Generally in the textbooks
30:47that I was reading in the early 80s,
30:49it was kind of assumed
30:51that chemical weathering
30:53was a function of rainfall,
30:55land area, temperature,
30:56these factors.
30:58And according to this logic,
31:00you would think that
31:02the Amazon rainforest, for instance,
31:04would have the most chemical weathering
31:06in the world because it had
31:08all these factors.
31:10But one day I was sitting in a class
31:12and one of the professors
31:14put up some numbers on the board
31:16and one of them struck me as
31:18these were numbers of river discharge
31:20of dissolved materials,
31:22so rock dissolved material.
31:24And it was a very high number
31:27and I started really digging into
31:29a lot of the recent literature.
31:31I realized that actually a lot
31:33of chemical weathering
31:35was going on in mountainous regions.
31:38Ramo wanted to find out
31:40exactly how much dissolved rock
31:42the rivers higher up
31:44in the Himalayas were carrying.
31:46Would it be enough to support
31:48her idea that these mountains
31:50helped bring about the ice age?
31:53For help in answering this question,
31:54Ramo turned to a colleague
31:56who specializes in collecting
31:58and studying water samples
32:00from all over the world.
32:03You have to work in pristine systems
32:05because what you're trying
32:07to understand is how the world
32:09works as a chemical system.
32:11So you have to go to remote areas.
32:13Then the problem you get into
32:15is one, just a brute force
32:17logistics problem.
32:19How do you get there?
32:21How do you move around?
32:22How do you get out?
32:24What do you eat?
32:26And the second problem is
32:28there's no supporting information.
32:30That's to say there won't be
32:32long records of the flow,
32:34which you need.
32:36There won't be long records
32:38of sediment transport.
32:40And there very often isn't
32:42a supporting information base
32:44of geology, vegetation type
32:46and even climate.
32:48Tibet is just such a place.
32:59Scientific field work here
33:01is still in its infancy.
33:03Weeks are spent getting to locations
33:05where data can be collected.
33:17But such distances seem short
33:19when compared to the travels
33:21of a nomadic Tibetan herders
33:23whose tribes have called
33:25the plateau home for centuries.
33:48For everyone on the road,
33:50meals are a simple affair.
33:52Noodles and dried yak meat.
34:03Although the plateau
34:05is familiar territory
34:07to its inhabitants,
34:09its vastness is both exciting
34:11and frustrating to scientists.
34:13There's huge areas of the plateau
34:15we know nothing about.
34:17It is ironic that it's played
34:19such an important role
34:21in the science in the last few years
34:23and we know so little about it
34:25and have so little access to it.
34:27On this expedition,
34:29Remo had the opportunity
34:31to collect water samples
34:33to learn how much weathering
34:35is going on here today.
34:38It's going to be very interesting
34:40actually to start at the top
34:42and go right through the Himalayas
34:44and see if there's any obvious change
34:47in the water chemistry
34:49as we go through those formations.
34:59Building a base of information
35:01about the region
35:03can be slow and tedious.
35:09Pinpointing the exact location
35:10where data comes from
35:12is difficult in uncharted places.
35:15But the process has gotten
35:17a lot easier in recent years.
35:19We've just taken a river sample
35:21and rather than writing it
35:23so many kilometers from some town
35:25that has a different name on every map,
35:27what we're doing is getting
35:29a satellite fix.
35:31And this little piece of plastic
35:33has an antenna in it.
35:3520,000 kilometers above us
35:37there's 24 satellites
35:38circling the earth.
35:40And this usually can pick up about five.
35:42And what it does is
35:44it picks up an incredibly faint signal
35:46from those satellites
35:48and calculates, triangulates
35:50the exact position for this spot.
35:57After more than a week on the road,
35:59the expedition came to
36:01a temporary standstill
36:03upon reaching Mount Kailash
36:05in western Tibet.
36:09Tibetans from all over
36:11make pilgrimages
36:13to this sacred mountain
36:15which they regard
36:17as the center of the cosmos.
36:19At least once in their lifetime
36:21they hope to walk around Kailash,
36:23an act of devotion
36:25that helps accumulate
36:27spiritual merit.
36:31The team paused
36:33for its Tibetan members
36:35to make this journey,
36:3618 hours straight.
36:42Afterwards,
36:44the expedition could begin again.
36:49For Ramo's explanation
36:51of the Ice Age
36:53to be taken seriously,
36:55it would have to be backed up
36:57with hard data.
36:59What she needed
37:01was a way to show
37:03that weathering of the Himalayas
37:04has never been so easy.
37:06So,
37:08she set out
37:10to the Himalayas
37:12in search of
37:14evidence
37:16to prove
37:18that the ice age
37:20has never been
37:22so easy.
37:24Ramo's expedition
37:26began
37:28with the discovery
37:30of a piece of
37:32ice
37:34that had been
37:36dissolved in
37:38calcium carbonate.
37:40The ice age
37:42is a time
37:44when
37:46the ice age
37:48is a time
37:50when
37:52the ice age
37:54is a time
37:56when
37:58the ice age
38:00is a time
38:02when
38:05there are
38:07at least
38:09two types
38:11or isotopes
38:13of strontium
38:15each with a
38:17different
38:19atomic
38:20mass.
38:21They can
38:23be separated
38:24in the lab
38:26and the
38:27concentrations
38:28of the
38:29isotopes
38:30in each
38:32layer
38:33and is released by seafloor spreading.
38:38Maureen Rameau reasoned that by comparing the amounts of the isotopes in the layers,
38:43she would learn which process was more active at any point in time,
38:47seafloor spreading or chemical weathering.
38:54This curve graphs the ratio of the two isotopes,
38:57strontium 87 to strontium 86,
39:00over the last 80 million years.
39:04Here was a measure of which mechanism was more powerful
39:08in controlling levels of carbon dioxide in the atmosphere.
39:15What we found as we got further into the strontium work
39:18was that the curve got more and more interesting.
39:21The problem was we weren't exactly sure what it meant.
39:25Now, it also turns out that at about the same time,
39:29Maureen Rameau and Ruddiman had come out with their ideas
39:34about how the Himalaya and the erosion of the Himalaya
39:39were affecting the Earth's climate.
39:41And they, in fact, used the strontium data
39:43as evidence that erosion and weathering rates were changing.
39:47And this was support for their ideas.
39:50From about 80 million years ago to 35 million years ago,
39:53almost nothing happened.
39:55And then at 35 million years ago, wham!
39:57The strontium curve starts to go up like a rocket in comparison.
40:01So if one was going to make a dividing line
40:04and say when was it the way it used to be
40:06and when did it start becoming like it is now,
40:09in other words, when was the Earth warm
40:11and when did it start to get cold,
40:13it would have been 35 million years ago.
40:15The strontium record was shouting that.
40:17If you stretch it a little bit,
40:19it's close to the time that India and Asia start to collide
40:22and one starts to build the Himalaya.
40:28But is the sudden increase in strontium-87
40:31washing into the ocean at the same time
40:33the Himalayas were forming more than coincidence?
40:40Maureen Rameau sees it as an important piece of evidence
40:43supporting her ideas.
40:47The strontium record was kind of the third piece of the puzzle,
40:51I guess, that fell into place that kind of made it all click.
40:54One was, you know, I knew the history of the uplift of the Himalayas,
40:57I knew there was a lot of chemical weathering going on here today,
41:00but I didn't really have any,
41:03you know, I didn't really have a really good geologic record
41:07of how chemical weathering had changed through time.
41:10And when I saw a strontium isotope curve for the first time,
41:13I saw it in me and I realized that this was kind of, you know,
41:17the smoking gun, so to speak.
41:21The strontium curve is controversial, though.
41:25Not everyone agrees on what it actually means.
41:28Critics point out that the rising amount of strontium-87
41:32may not be due to an increase in chemical weathering.
41:38It could be rising simply because more rocks rich in strontium-87
41:43happen to become exposed on the surface of the Himalayas.
41:46Useful geochemical analysis to see if it's similar geochemistry.
41:51In fact, such rocks are plentiful in the region.
41:55I'm going to whack it off. No, we're getting there.
41:58The granites formed in the Himalayas
42:01are exceptionally high in 87 strontium.
42:06So what we've got here is a ready source available at the surface
42:11to provide the increase in 87 strontium seen in the oceans.
42:17Tibet
42:23The strontium evidence remains open to interpretation.
42:27But another clue to solving the mystery of Tibet's role in the Ice Age
42:31may lie just a few days' drive away.
42:37In a small town on the Tibetan plateau,
42:39the team met up with some local geologists and fossil hunters
42:43who had found a rock that they thought might be helpful.
42:47Where did you get this, Lao Pang?
42:49Where did you get this?
43:06He said he found it in the Tertiary Basin,
43:09north of Daqing in the Kailash area.
43:18He said originally he thought it might be a stem of a plant,
43:22but now he compared that with the fossils which have been collected,
43:28and this one has been identified as a reed
43:32growing on the side of a riverbank here.
43:37A fossil plant, such as a reed that grew by the side of a riverbank,
43:42reveals what the climate was like when the plant was alive.
43:46A comparison to the same area today reveals how conditions have changed.
43:53With enough plant fossils,
43:55scientists can build a record of these changes over time.
44:00This could help settle another mystery.
44:03Exactly when did the uplift of the region occur, and how quickly?
44:11The answers to these questions are vital to linking the Himalayas to the Ice Age.
44:16What we really want to know is what the elevation history of the Tibetan plateau is,
44:21and one of the ways that we think we may be able to get at this is using paleobotany.
44:27The idea behind this idea is when you climb up a mountain,
44:30you go through progressively different vegetation bands.
44:34Obviously it's a lot colder at the top of the mountain, the vegetation is very different,
44:38and so possibly what we can do is look at fossils of past plants
44:43that are very high up in the plateau
44:45and try to infer what the elevation of those plants were at the time that those plants grew.
44:53So for instance, in extreme case, you'd find a palm tree at five kilometers,
44:57and that palm tree is Miocene 15 million years ago.
45:00Does that mean that 15 million years ago the plateau is much lower at sea level where palm trees grow?
45:07But can you really distinguish warm weather plants from cold weather plants in the fossil record?
45:11If you look at tropical plants, the leaves are generally thick, they're often large,
45:17their margins are very smooth, these are called entire margins.
45:22Whereas if you look at temperate plants, often the leaves are thin,
45:26which is difficult to record in the fossil record,
45:28but their margins are often irregular, not all of them, but often irregular.
45:32They have teeth on the margins, they go around, teeth around the edge.
45:36You think of a maple leaf or an oak leaf, you have teeth around the edges.
45:41Those are parameters that we can measure.
45:43Will you ever be able to find enough fossils and date them well enough?
45:47No, that's another question.
45:48No, that's the critical question.
45:50Just a minute, we're in the middle of Tibet now, is this going to work for us?
45:53How are we going to establish at what time the altitude of Tibet was at what level?
46:00Altitude is one problem, temperature is another.
46:04Both are essential to understanding whether the uplift of the Tibetan plateau caused the ice age.
46:13I see no reason why we shouldn't be able to trace back in Tibet over the last 20 million years or whatever,
46:19the variations in temperature.
46:21How we translate that into variations in altitude, that's a matter for debate.
46:25But as a method for predicting variations in temperature, it seems very powerful indeed.
46:31Well, I personally think it's the only way.
46:34And it won't work indeed if there are too few species represented.
46:40Six is not enough.
46:41We need 20. 20 is a rough minimum.
46:44Whether there are enough fossil localities, that's a good question.
46:49To develop a reliable record of the history of the region's elevation by this method
46:53would require a wide range of plant fossils.
47:01Because this area is so inaccessible, many years and many more expeditions would be required.
47:12Field work in these conditions is never easy.
47:20The roads are notorious for contributing to the slow pace of science.
47:25And it is not just the views that leave visitors short of breath.
47:29Working at 15,000 feet is debilitating.
47:37Despite how much basic information has yet to be discovered about this region,
47:42Maureen Ramo remains steadfast in her opinion that the Himalayas caused the ice age.
47:48The Himalayas are unique because they're so huge.
47:52They're so high.
47:53So much crust has been thrust up into the atmosphere.
47:56So much of it has been eroded.
47:58An enormous amount of mechanical and chemical weathering has gone on in this mountain range.
48:02It's like a huge sponge pulling CO2 out of the atmosphere.
48:07I think these mountains are in large part responsible for all the global cooling of the last 40 million years.
48:14With the addition of the strontium evidence, Maureen Ramo thought she had solved the ice age mystery.
48:23First, the uplift of the Tibetan region intensified the Indian monsoon.
48:29Then the monsoon rains eroded the mountains, stripping carbon dioxide from the air.
48:34Finally, with less carbon dioxide, the atmosphere got colder and colder.
48:40The only thing left to do was publish the idea.
48:44I went back home and, like, wrote a paper.
48:47The paper was an agonizing ordeal, but I went back home and just started writing it.
48:54It was short to the point.
48:58Some scientists loved it. Others were less enthusiastic.
49:04The original paper by Ramo and co-workers in 1988
49:08specified that if we had uplift of the Himalayas,
49:11that the carbon dioxide would be consumed by weathering and CO2 would go down.
49:15Well, you can't just do this simply because you have to watch out.
49:18You run out of CO2 very quickly.
49:20The geochemists are an unruly bunch.
49:23They have sharp knives, and if you're wrong, it can be a very public matter.
49:29There was a lot of things in that paper that were very controversial.
49:33I think there's good reasons for why the reaction is mixed.
49:37On one hand, I think some people think,
49:39well, gee, could it really be that simple and I missed it?
49:42Or the other thing is, well, she can't know enough about this to really get it right,
49:49so we are justified in not paying attention to it.
49:53But the fact is that it tweaks everybody.
49:56I mean, one of the people that was on my thesis committee
49:59just basically said the paper was unpublishable crap.
50:02So, I mean, I got a lot of conflicting advice on that paper.
50:06Some people said, oh, this is great.
50:08Other people said, this is crock.
50:10Scientists are men, unfortunately,
50:12usually men in white coats seeking after truth about 1% of the time.
50:17The rest of the time, they're like everybody else.
50:20So if you spent the last 10 years making more and more elaborate models or experiments, whatever,
50:28it's not just modelers,
50:31and somebody comes along and says that's all by the way
50:36because you're not addressing this and this is what's really the big problem,
50:40then the response isn't open-handed enthusiasm.
50:44There's something about it that's undeniable,
50:47and that is that if you erode continental rocks,
50:51you should take away CO2 from the system.
50:54And if you look at the geologic record,
50:57there's been a lot of erosion in the Himalaya,
51:00and I don't think erosion was there before the Himalaya formed,
51:03so there's been some change since they came up.
51:09But if you look at the other models for how the climate system works,
51:13you're almost completely at odds with this idea.
51:16And there's a real scientific problem.
51:20So on the one side, if you listen to Maureen,
51:23she will tell you a story that you have a hard time arguing with.
51:26And if you go to another person, for example, Bob Berner,
51:29he will tell you a story that's almost completely at odds with what Maureen will tell you
51:34and give you good reasons why that has to be the case.
51:37And so we have a problem.
51:43Things are definitely not perfect with my theory.
51:45There's major areas where I don't have an answer.
51:51But I think that, you know, that I'm going in the right direction,
51:56and I think I know what the problems are and how to go about trying to solve them.
52:02She says, hopefully.
52:05Rameau and her colleagues have added to the possible explanations of the Ice Age.
52:10But the mystery is far from solved.
52:17If you put up a theory with no fact,
52:20it probably doesn't affect anybody.
52:24It just gets ignored.
52:26And she, of course, has not done that.
52:28She's got a lot of facts to back it up.
52:30But we still have a ways to go.
52:32Science, the forefront of science is a very fuzzy, fuzzy area.
52:36And one needs a balance of all kinds of approaches.
52:41There have to be ideas drifting around.
52:43They have to be formulated and worked up well.
52:45And usually, when they are, there still aren't enough facts.
52:51So while scientists continue to accumulate facts that tell us about our climate's history,
52:57some cannot resist speculating about its future.
53:00If I was asked about what the climate was likely to do in the future,
53:04I would probably focus on the last two million years of the strontium curve,
53:08during which time the strontium ratio has gone up at a rate that's as close to as fast as it's ever gone up.
53:15And in the past, when that's happened,
53:17it's meant that the climate is going to get colder in a couple of million years.
53:22So my prediction would be that we haven't seen the most intense Ice Age yet.
53:28It would be a heck of a story if it turned out to be true.
53:58The highest plateau, the deepest canyon.
54:01Take on Tibet's extremes of land and weather at NOVA's website.
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56:19On patrol in the Persian Gulf.
56:21Tensions remain high.
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56:39Next time on NOVA.