Novel agro-pastoral package enabled settlement of Tibetan Plateau

Barley and sheep enabled agriculturalists to live at high altitude

A new study, published in the journal Science, has documented human adaptations to living at high altitudes on the Tibetan Plateau. This vast elevated region in Central Asia includes most of Tibet and Qinghai Province, together with a part of the Ladakh region of Jammu and Kashmir. Measuring 1,000 km (620 miles) from north to south and 2,500 km (1,600 miles) east to west, it has an area of 2,500,000 sq. km (970,000 sq. miles) or roughly five times the size of France. With an average elevation exceeding 4,500 m (14,800 ft.), the Tibetan Plateau is the world’s highest and largest plateau, for which reason it is popularly known as “the roof of the world”.

The first evidence for human presence on the Tibetan Plateau dates to around 20,000 years ago, reaching altitudes of up to 4,300 metres above sea level. Artefacts include stone tools, small hearths and animal remains. It is thought that these finds were associated with single-use campsites occupied by hunters in pursuit of game. The first farming villages appeared 5,200 years ago.

In order to ascertain when and at what altitude food production became sufficient to sustain a long-term presence, researchers recovered artefacts, animal remains and plant remains from 53 sites located on the northeastern corner of the plateau. They obtained radiocarbon dates for charred cereal grains recovered from each site, which suggested that the sites fell into two groups. The first group dated from between 5,200 to 3,600 years ago, and the second group from between 3,600 to 2,300 years ago. None of the first group of sites exceeded an altitude much above 2,500 metres above sea level, but the majority of second group of sites ranged in altitude from between 2,500 to 3,400 metres above sea level.

The first group of sites were interpreted as reflecting the widespread settlement of the region by farming communities of the Yellow River and its tributaries. Millet accounted for all but a tiny percentage of cereal grains recovered from these sites. By contrast, at the higher altitude sites in the second group, the dominant crop was barley, together with some. Barley was grown alongside millet at the lower altitude sites in the second group. Sheep remains were present at those sites lying at or higher than 3,000 meters above sea level.

The presence of crops and livestock suggests that there was now a more sustained human presence at high altitudes. Barley is more frost-resistant than millet, but it also has a longer growing season of typically six months. The presence of houses and tombs at these sites further supports a sustained and likely year-round human presence. Thus this second phase of settlement of the Tibetan Plateau saw the northern Chinese millet joined and in some cases replaced by two Southwest Asian crops – barley and wheat. The introduction of these new crops enabled Tibetan farmers to exploit the harsher conditions of the higher elevations of the Tibetan Plateau.

Some sites outside the study region were located at even greater altitudes. For example, Changguogou on the southern-central part of the plateau has an elevation of 3,600 metres above sea level. Southwest Asian crops included barley, wheat, oats, rye and peas, in addition to millet.

The changing patterns of exploitation of the Tibetan Plateau might have been driven by climate change. The warm, wet conditions of the Early and Middle Holocene enabled both early hunter-gatherer exploitation of the plateau and the subsequent expansion of millet agriculture into the region. These conditions gave way to a colder, dryer climate, which did not favour millet and forced farmers to look for hardier alternatives. Not only did barley and wheat do well in the cooler conditions, they also grew at the higher elevations the farmers had previously been unable to exploit.


1. Chen, F. et al., Agriculture facilitated permanent human occupation of the Tibetan Plateau after 3600 BP. Science (2014).


Ice Ages

Introduction: We live in an era where even politicians have realised the significant threat climate change poses to civilization and indeed to all life on Earth, but it is nothing new and has been a major driving force of evolutionary change for hundreds of millions of years. One species that undoubtedly owes its very existence to climate change is Homo sapiens. It is no coincidence that the earliest human species, Homo habilis, emerged at just about the same time as Earth entered an ice age. The subsequent epochs of advancing and retreating ice sheets have played a pivotal role in the evolution and dispersal of subsequent human species, culminating in that of modern humans, Homo sapiens.

The Current Ice Age: We now know that the Earth has been affected by a number of ice ages in its history. The current Ice Age begun 2.6 million years ago and has been characterised by the advance and retreat of major glaciers and ice sheets in glacial periods punctuated by warmer interglacial periods. The last glacial period – or what is popularly known as the last Ice Age – began 110,000 years ago and ended with the onset of the Holocene epoch 11,600 years ago. The Ice Age is not in fact at an end and barring the effects of global warming, the glaciers and ice sheets will one day return.

The origins of the current Ice Age go back some 50 million years. Throughout this time the Earth’s climate has been cooling. Though the reasons are not fully understood, the collision of India with the Eurasian landmass (48-52 million years ago) and the migration of Antarctica to the South Pole (23 million years ago) are thought to be factors. From the first of these two events arose the mountains of the Himalaya Range, uplifted by the collision. The weathering of this new mountain range sequestered CO2 from the atmosphere, leading to global cooling. Subsequently the presence of a large landmass at the South Pole encouraged the build-up of ice. These ice-sheets reflected more of the Sun’s radiation back into space leading, in turn, to further cooling. The tipping point was reached 2.6 million years ago, with the expansion of ice sheets in the Northern Hemisphere.

Discovery: Perhaps surprisingly, the discovery that the northern glaciers had once been far more extensive, reaching as far south as London, New York and Berlin, is comparatively recent. Not until the 19th Century did geologists began to ponder such anomalies as bones of reindeer in the south of France and granite boulders high up on the slopes of the predominantly limestone Jura Mountains. The German-Swiss geologist Jean de Charpentier suspected that the boulders might have been deposited there by glaciers. He discussed the idea with his friend and fellow geologist Louis Agassiz, who took it up with great enthusiasm.

Meanwhile the naturalist Karl Friedrich Schimper, who was also a friend of Agassiz, was also of the opinion that ice sheets had once been far more extensive than now, and had once lain across much of Eurasia and North America. But he was a man who very rarely put his ideas into writing. He did however lend Agassiz his notes, but to his and de Charpentier’s considerable annoyance Agassiz subsequently took all the credit for the theory, which he put forward in a two-volume work entitled Etudes sur les glaciers (Study on Glaciers), published in 1840.

The main problem with the theory as it stood was that it offered no explanation for the cycles between glacial and interglacial periods. That these might have an astronomical cause was first suggested by Scottish scientist James Croll in 1860, who claimed that cyclical changes in the Earth’s orbit around the Sun might be responsible. Croll’s theory attracted considerable interest at the time, but had been more or less abandoned by the end of the 19th Century. The theory was revived and extended in the 1920s and 1930s by a Serbian engineer named Milutin Milanković.

The Milanković Pacemaker: The Earth’s seasons arise from its axis of spin being tilted rather than upright in relation to the plane of its orbit. When either the Northern or the Southern Hemisphere is tilted towards the Sun, it will experience summer as a result of both longer hours of daylight and the Sun being higher in the sky and more of its heat reaching the ground. The other hemisphere, meanwhile, will experience winter. For the Northern Hemisphere, the day with the longest period of daylight or Summer Solstice occurs on 21 June. The day with the shortest period of daylight or Winter Solstice occurs on 21 December. The spring and autumn equinoxes occur when the Earth is mid-way between the solstice positions, and everywhere receives 12 hours of daylight.

At the present time in the Northern Hemisphere, summers are hot enough to melt the whole of the previous winter’s accumulation of snow, but if this was not the case then the latter would gradually build up and ice sheets would advance into temperate latitudes. The enlarged ice sheets would then reflect more of the Sun’s radiation straight back into space, causing the cooling process to accelerate.

Milanković considered the possible effects of astronomical cycles on the intensity of the seasons, the amount of sunlight received (“insolation”) in the Northern Hemisphere and the possibility that at certain times the summers in the Northern Hemisphere might not be hot enough to prevent ice sheets from building up. He took into account three variables now known as the Milanković Cycles: precession of the equinoxes; variation of the axial tilt (“obliquity”) and changes in the shape of the Earth’s orbit around the Sun (“eccentricity”).

Precession is the long-term oscillation experienced by the Earth in which the spatial orientation of the axis changes with time. The phenomenon may be likened to the wobbling of a spinning-top or a gyroscope and is caused by caused by tidal effects of the Moon and Sun. A complete cycle takes 25,800 years. Precession affects the time of the year when the Earth is at is closest to the Sun (“perihelion”), which in turn will affect the intensity of the seasons. The picture is complicated by the precession of the orbit itself, with the perihelion slowly migrating around the Sun in a 105,000 year cycle. If these are combined with cyclical changes in the shape of the Earth’s orbit, a periodicity of 21,700 years is obtained for perihelion coinciding with summer in each hemisphere.

The Earth’s axial tilt is currently 23.5 degrees, but varies between 21.8 and 24.4 degrees over a period of 41,000 years. The seasons for both hemispheres will be exaggerated when the angle of tilt is high and moderated when it is low.

Finally the Earth’s orbit changes from near-circular (“low eccentricity”) to an ellipse (“high eccentricity”) with a major cycle of 400,000 years and a number of smaller cycles that average out at 100,000 years. At times of high eccentricity, the seasons are exaggerated in the hemisphere experiencing summer close to perihelion, and moderated in the other.

How these differing cycles combine to either exaggerate or moderate the seasons is of course very complicated, and Milanković spent many years laboriously performing the relevant calculations which – in an era before computers – all had to be carried out with the aid of a slide rule and books of tables. Unfortunately his dates for glacial periods did not tally with the then accepted values, and his theory fell out of favour. However in the late 1960s and early 1970s advances in methods for dating proxy evidence (indications of glacial periods) vindicated Milanković’s predictions and his theory gained widespread acceptance.

Although the duration of glacial periods is now seen to correspond closely to expectations, different cycles seem to have dominated at different times. Prior to 800,000 years ago, glacial periods followed the 41,000 year obliquity cycle, but subsequently the 100,000 year orbital eccentricity cycle has been dominant.

Effect upon Sea Levels: During glacial periods, significant amounts of water are locked up in ice sheets and sea levels fall. At the time of the Last Glacial Maximum (LGM), when the ice sheets reached their maximum extent, 20,000 years ago, sea levels were roughly 120 metres below their present-day level. Britain and Ireland were joined to continental Europe and the Indonesian islands as far east as Borneo and Bali were joined to mainland Asia as part of a subcontinental landmass known as Sundaland. Australia was connected to New Guinea and Tasmania and though it remained separate from Sundaland, the gap was small and could be crossed by humans living at that time.

Effect upon Climate: During the LGM, the climate throughout the world was cooler and dryer. The arid conditions were a consequence of so much water being locked up in ice sheets. In some parts of the world such as Southern Australia and the Sahel Belt south of the Sahara, rainfall dropped by up to 90 percent. Throughout the world deserts expanded and rainforest shrank.

During interglacial periods, the climate is warmer and wetter. In Africa, a weather phenomenon known as in Inter-Tropical Convergence Zone (ITCZ), which normally brings monsoons to the tropics, can extend its influence northwards. During such epochs, the Sahara experiences moist wet conditions and savannah climate. The last such climatic optimum was the Holocene Thermal Optimum, which began at the end of the last glacial period and peaked around 4000 BC. Subsequently, Milanković-determined insolation declined, the ITCZ returned southwards and the Sahara rapidly dried up.


Bryson, B. (2003) A Short History of Nearly Everything, Doubleday.
Evans, E.P. (1887) The North American review, Volume 145, Issue 368, July 1887.
Klein, R. (1999) The Human Career (2nd Edition), University of Chicago Press.
Wilson, R.C.L., Drury S.A. and Chapman J.L. (2000) The Great Ice Age, Routledge.

© Christopher Seddon 2008

The End is Nigh!

The Day the Earth Caught Fire (1961) & Crack in the World (1965)

During the 1960s, the Bomb, as it was simply known, held very much the same place in public consciousness as global warming does today. The fear of nuclear war was very real and even though the Cuban Missile Crisis had shown that the US and USSR could pull back from the brink, there remained the possibility that a nuclear war could be started by accident. Hollywood’s output reflected this fear with Stanley Kubrick’s black comedy Dr. Strangelove and the documentary-styled Failsafe, both released in 1964.

The possibility that mankind might be placed in peril simply by the testing of nuclear weapons or indeed by an attempt to make benign use of them was less prominent in the public imagination; nevertheless this sub-genre gave rise to two excellent “doomsday” movies: the British-made The Day the Earth Caught Fire (1961) and the US-made Crack in the World (1965).

The Day the Earth Caught Fire is an offbeat but smart piece of movie-making. It was directed and produced by the late Val Guest, who also directed the first two screen-adaptations of the Quatermass series. Screenplay was also by Guest, in conjunction with Wolf Mankowitz. The film starred Janet Monroe, Leo McKern and Edward Judd, and featured former Daily Express editor Arthur Christansen playing himself. It was filmed in black and white, with some orange-tinted sequences.

The tinted opening of the movie shows journalist and reformed alcoholic Peter Stenning (Judd) making his way down a deserted, heat-baked Fleet Street to the Daily Express building, to cover what may well be the last news story ever. Four nuclear devices, the most powerful yet devised, have just been detonated in an attempt to push the Earth back into its proper orbit. It is too early yet to tell if the attempt has been successful.

Reverting to conventional b/w, the main section of the movie then tells the story of the events of the previous 90 days, beginning with near-simultaneous bomb tests by the United States and the Soviet Union. In the days that follow, earthquakes and freak weather conditions occur in many parts of the world, and a total eclipse of the sun is seen in London ten days before it was due. Soon after, the whole world begins to experience heat-wave conditions. London experiences thick fog, followed by violent storms.

These events are seen through the eyes of Stenning and fellow journalist Bill Maguire (McKern). Stenning’s relationships with his ex-wife (who left him for another man), his son and new love Jeannie Craig (Monroe) are skilfully worked into the story, forming an integral part of the narrative drive. Encouraged by Editor Arthur Christiansen (himself), Stenning and Maguire, with assistance from Craig, eventually expose a government cover-up. The bombs have caused an eleven-degree shift in the tilt of the Earth’s axis. The Prime Minister goes on the air to reassure the public that the Earth’s axial tilt has altered in the past without catastrophic effects, and that things will eventually settle down.

But temperatures continue to rise inexorably. Water rationing is brought in and the Thames dries up. Eventually Christiansen learns from a Russian correspondent that that the bomb tests have also affected the Earth’s orbit, and it is moving towards the Sun. With doomsday just four months away, the Prime Minister goes on the air again to inform the public that the heads of governments world-wide have decided that the only hope for mankind is to detonate four very large nuclear bombs, in order to reverse the motion towards the Sun. Meanwhile, law and order is breaking down. People are coming down with typhoid from contaminated bootleg water and bottles of Coca Cola are fetching four pounds (about £80 at today’s prices). A street party held the night before the corrective bombs are detonated gets out of hand and rioting breaks out.

The countdown is broadcast to an anxiously-waiting world by radio, by loudspeakers set up in the streets of cities around the world, and by producer-gas fuelled police cars on the streets of London. Stenning, Maguire and Craig follow events from the Old Bell, Fleet Street [a pub in which I have spent many hours!] and the bombs are detonated, through the only immediate effect is a that cloud of dust is shaken up. Stenning begs Maguire to let him cover the story.

The story returns to the tinted “frame” that began the film. Stenning dictates his copy, his typewriter having seized up. A camera pans between two versions of tomorrow’s front page, ready to go to press. One reads “World Saved”, the other “World Doomed”. Several shots show clocks, both inside and outside the building, each showing a later time than the last, suggesting the passage of time. Church bells ring out across the City of London, implying that the Earth was saved.

It has been suggested that the church bells were added at the insistence of the distributer, and Guest intended a completely open ending. In a director’s commentary to the DVD edition, he does not mention the ending. Val Guest died in 2006, aged 94.

The Day the Earth Caught Fire is the definitive “cult movie”, a term that should be reserved for movies that punch above their weight, while delivering what they set out to deliver. This film does just that: in addition to the intelligent screenplay, the special effects belie the small budget, especially the scenes where Thames dries up. Londoners will particularly appreciate the location filming around the capital.

The film is not without some “bad science”, however. Nuclear bombs could not possibly affect the Earth’s orbit. A major meteorite impact, such as the one that wiped out the dinosaurs, would be many times more powerful than the world’s combined nuclear arsenals, but it would have a negligible effect on the orbit. Indeed, anything powerful enough to affect the Earth’s orbit to the extent implied by the film would almost certainly destroy the planet at the outset.

A solar eclipse can only take place at New Moon and one occurring ten days early would not happen without warning, as it would be apparent for days in advance that something was seriously wrong with the Moon’s phases. Four days before the eclipse, the Moon would have been seen as a waning crescent when it should still have been full. This would be noticed by astronomers and indeed any casual observer in possession of a diary or calendar. The anomaly would certainly have been picked up at a newspaper, where the current phase of the Moon is often published with sunrise and sunset times.

A eleven degree alteration of the Earth’s axial tilt would significantly alter sunrise and sunset times around the world, and postions of constellations in the night sky. Again, this would be widely noticed almost immediately.

Made four years later, Crack in the World is a more orthodox SF/disaster movie. It starred Dana Andrews, Janette Scott, Keiron Moore and Alexander Knox. The screenplay was by John Manchip White and Julian Zimet. The film was shot on location in Spain and its memorable score was composed by Johnny Douglas.

Project Inner Space is an international effort to tap geothermal energy by drilling down to the Earth’s mantle, but attempts are being frustrated by a layer of dense material lying at the boundary between it and the crust above. The project’s director, cancer sufferer Dr. Stephen Sorenson (Andrews) wants to use an atomic bomb to blast through the obstruction, and a government team headed by Sir Charles Eggerston (Knox) travels to the Project’s site, a massive complex two miles underground, to consider Sorenson’s plan. This is supported by nearly all the Project’s scientists, including Sorenson’s wife Dr. Maggie Sorenson (Scott). The one dissenter is Maggie’s former lover Dr. Ted Rampion (Moore), who has developed a “Rampion Theory” that the Earth’s crust has already been seriously weakened by underground nuclear testing, and that Sorenson’s plan would trigger a global catastrophe.

Despite Rampion’s objections, the attempt goes ahead but shortly before it does Sorenson learns that his illness is terminal. However he bravely keeps this knowledge to himself. The bomb does blast through the obstruction, and magma bubbles to the surface. All appears to be well, and Rampion happily concedes that he was wrong.

However a series of earthquakes begin to occur along a (fictitious) geological flaw in the Earth’s crust known as the Macedo Fault. Many of the places affected have no history of seismic disturbance. Rampion and his assistant Steele take a DSV to investigate an underwater portion of the fault and determines that a spreading crack has opened up in the Earth’s crust. If a way of stopping the rupture isn’t found, the Earth will be torn apart.

Sorenson and Rampion put aside their differences and try to come up with a solution. They decide the best hope of averting disaster is to explode a hydrogen bomb in the shaft of an active volcano that lies in the path of the spreading crack. Rampion and Steele volunteer for the difficult assignment of lowering the bomb into the volcanic shaft.

The bomb is successfully placed, though Steele falls to his death in the volcano’s magma chamber, and Rampion is almost barbecued alive. Believing him to be dead, Maggie Sorenson is distraught. Still unaware how seriously ill her husband is, her affections are drifting back to Rampion. However, the latter is only unconscious and rapidly recovers. The bomb goes off and the earthquakes appear to cease.

Relief is short-lived. Soon reports come in that suggest that the crack has simply switched direction, and appears to be doubling back on itself. To make matters worse, it is now moving twice as fast. As Rampion speaks to Sorenson by R/T, the latter collapses – it is finally apparent that he seriously ill. The group returns to the Project, where Maggie learns her husband has just days to live. Despite her renewed feelings for Rampion, she is grief-stricken. However she accompanies Rampion in a jeep on a trip to investigate a second crack that has appeared near the Project complex [where exactly this is located is never revealed]. Meanwhile, Sorenson determines that the two cracks will meet at the original borehole, and that a portion of the Earth will be blasted away into space to form a new moon.

On the surface, Rampion and Maggie Sorenson desperately try to stop a train that is heading straight towards the crack, but the jeep goes into a ditch. The train fails to stop and a bridge it is travelling over collapses. There are no survivors.

After freeing the jeep, the pair return to the Project, which is being evacuated. There is a dramatic shot of two converging cracks. Nobody has seen Sorenson, so Rampion and Maggie take the elevator down into the by-now quake-torn complex to look for him. They find him preparing to record the birth of Earth’s new moon. He points out that the Project is located outside the area that will be blasted into space, locks himself in and refuses to leave. Rampion and Maggie Sorenson head back to the surface, but the elevator becomes jammed by a quake. They manage to climb to the surface and reach safety just as the two cracks meet. A colossal explosion blasts the new moon into space, at the same time acting as a safety valve to prevent any further earthquakes. Calm returns and the old Moon and its new sibling are seen in the sky together for the first time.

The science in Crack in the World is well thought out, but became dated soon after the film’s release as the theory of plate tectonics became widely accepted. There are in fact many “cracks in the world”, corresponding to the tectonic plates that slide over each other to cause continental drift.

The theory that the Moon was spun off from the Earth was first put forward by Sir George Darwin (son of Charles) in the 19th Century and was strongly supported by the American astronomer William Pickering, who suggested that the Atlantic basin had been formed as a result. However the angular momentum of a system so formed would not correspond to that of the actual Earth-Moon system, so the theory had to be abandoned.

Dated though the science is, it is certainly on another level to the ludicrous Core (2003).

For some reason, Crack in the World has never been released on DVD. It is strongly to be hoped that this omission will be rectified in the near future.

In recent years, there has been a trend for remaking classic movies of the 1950s and 1960s, such as the 2005 version of The War of the Worlds. The Day the Earth Caught Fire and Crack in the World would both be excellent candidates for a remake. Although both films are rooted in ‘Sixties fears about the Bomb, they additionally tap into two highly-topical themes – climate change and emission-free energy.

© Christopher Seddon 2008