IELTSwithJurabek

You should spend about 20 minutes on Questions 14-26, which are based on Reading Passage 2.

The Myth of the Eight-hour Sleep

14 We often worry about lying awake in the middle of the night - but it could be good for you. Indications from both science and history suggest that the eight-hour sleep may not be a natural or inborn pattern for humans. In the early 1990s, psychiatrist Thomas Wehr conducted research which implies just that.

Wehr kept a group of people in a darkened room for 14 hours a day for a month. It took some time for their sleep to regulate, but by the fourth week the subjects had settled into a very distinct sleeping pattern. First, they slept for four hours, then woke for one or two hours before falling into a second four-hour sleep. Though sleep scientists were impressed by the implications of the study, the idea that we must sleep for eight consecutive hours persists amongst the general public.

15 In 2001, historian Roger Ekirch of Virginia Tech University in the US published a paper drawn from 16 years of research, revealing historical evidence that humans used to sleep in two distinct periods of time each night. Ekirch's research found more than 500 references to a segmented sleeping pattern - in diaries, court records, medical books and literature, from the ancient Greeks to tribes in Nigeria. Much like Wehr's findings, these references describe a first sleep which began not long following sunset. Then there was a waking period of one or two hours and after that a second sleep. During the waking period, people could be quite active. They sometimes got up and moved around the house, although most people stayed in bed, and perhaps read or wrote if they had enough money for candles. In many historic accounts, Ekirch found that people used the time that they were awake between periods of sleep to think about and attempt to analyse their dreams. In his book, Evening's Empire, historian Craig Koslofsky suggests an explanation for this divided sleep pattern in Europe. 'Associations with night before the 17th century were not good,' he writes. He goes on to explain that the streets of the cities and towns at night were often populated by thieves or worse. The streets at night consequently scared many people. Even the wealthy, who could afford to light their way, had better things to spend their nights on.

16 Ekirch found that references to the first and second sleep started to disappear during the late 17th century. The pattern began to alter first among the upper classes in northern Europe and, over the course of the next 200 years, began changing amongst the rest of Western society. By the 1920s, the idea a first and second sleep had receded entirely from our social consciousness. Ekirch attributes the initial shift to improvements in street and home distincting. As the night became a time for all kinds of activity, the length of time people sleep declined. In 1667, Paris became the first city in the world to light its streets, using wax candles in glass lamps. It was followed by another French city, Lille, in the same year and by Amsterdam in Holland two years later, where a much more efficient oil-powered lamp was developed. London didn't light its streets until 1684, but by the end of the 17th century, more than 50 of Europe's major towns and cities were lit at night. Coffee houses emerged as a fashionable phenomenon and many were open virtually around the clock. Going out at night became commonplace, and spending hours lying in bed was considered a waste of time. 'People were becoming increasingly time-conscious and sensitive to efficiency, certainly before the 19th century,' says Ekirch. 'But the Industrial Revolution intensified that attitude considerably.' Strong evidence of this shifting attitude is contained in a medical journal from 1829 which urged parents to force their children out of the pattern of first and second sleep.

17 Today, most people seem to have adapted quite well to the eight-hour sleep, but Ekirch believes many sleeping problems may have roots in the human body's natural preference for divided sleep, as well as in difficulties caused by extended exposure to artificial light in the modern world. This could be the cause of a condition called sleep maintenance insomnia, where people wake during the night and have trouble getting back to sleep. The condition first appears in literature at the end of the 19th century, at the same time as accounts of interrupted sleep disappear.

18 Sleep psychologist, Gregg Jacobs, says that the idea that we must sleep for an extended period of time could be damaging if it makes people who wake up in the night anxious, as this anxiety can itself discourage sleep and is likely to affect waking life too. Jacobs suggests that the waking period between sleeps, when people simply rested and relaxed, could have played an important part in the human capacity to regulate stress naturally. Russell Foster, a professor of circadian (body clock) neuroscience at Oxford University in the UK, shares this point of view. 'Over 30% of the medical problems that doctors are faced with stem directly or indirectly from sleep. But sleep has been ignored in medical training, and there are very few centres where sleep is studied,' Foster says. He feels this needs to change.

READING PASSAGE 3

You should spend about 20 minutes on Questions 27-40, which are based on Reading Passage 3 below.

Living dunes

Things don't come much stranger than heaps of sand that can move and sing of their own accord. Sally Palmer investigates

A 27 Armies of giant sand dunes are advancing across the world's deserts, engulfing anything that crosses their path. They are tens of metres tall and hundreds of metres long. Fortunately, they aren't going very fast. Even the smallest, speediest dunes only travel about 100 metres over the course of a year, while the bigger ones, which weigh something in the order of 10,000 tonnes, barely move one metre in that time. However, their insidious creep can have serious consequences if there is an oil installation or a railway line in their path.

B 28 About 47% of the world's land mass, including Antarctica, most of Australia and large areas of Africa, is classified as arid or semi-arid desert. Only around 20% of that is sand-covered, however, and over half of that is classified as 'linear' sand dunes. These form in a long curving wave, as a result of wind blowing strongly from several quarters, flipping them from side to side. Although linear dunes are static, sand blowing off them can cause problems for desert villages, burying crops and buildings.

C 29 Moving dunes make up just a small percentage of the rest, but they are of the most interest to scientists. They are known as 'barchans': heavy, crescent-shaped sand piles with a ridged crest and two elongated arms, one curving away to either side. 'Barchan dunes only tend to form where you have one-directional winds on the edge of sandy deserts near coastal areas,' says Giles Wiggs, a geomorphologist at Oxford University, who has been studying the formation and movement of sand dunes for more than a decade.

D 30 But even with strong winds, how can entire barchans move while retaining their form? That question was first answered in the mid-20th century by British explorer Ralph Alger Bagnold, and his answer hinges on the fact that dunes aren't solid, but granular. Bagnold figured out how barchan dunes are able to move grain by grain. Imagine a single grain of sand being blown up the back of a dune by the wind and deposited on the top. More grains follow the same pattern, until the accumulated weight of piled-up sand finally pushes the top down the dune face. The grain tumbles, then stops on the face until subsequent mini-avalanches bury it. Eventually, it reappears at the back of the dune, ready to repeat the process. As this happens to every grain of sand in the dune, the whole thing creeps in the direction of the prevailing wind.

E 31 The relationship between the wind and barchan dunes is complex. As a dune grows, it modifies the speed and course of the wind, which in turn alters how that dune and its neighbours evolve. 'Interestingly, the dune can regulate its own shape, and maintain it as it moves,' says Dr Stephane Douady, a physicist at Ecole Normale Superieure (ENS) in France. 'Even when two dunes collide, they quickly take on their distinctive shapes again. It's like a living organism.'

F 32 Douady and his colleagues have also been studying an even odder phenomenon than moving dunes: some barchans actually sing. Local legends attributed the sounds to dangerous spirits which were trying to trap unwary travellers. Douady is more pragmatic. 'It's a strong booming noise with a low frequency,' he explains, making a noise like a foghorn to demonstrate. 'It can last for a long time - up to several minutes. It's a very loud sound and you don't understand where it's coming from when you first hear it.' There are about 50 dunes distributed across 35 deserts round the world that are known to sing. Douady says the sound is caused by the way sand avalanches down the faces of particular dunes. Rather than tumbling randomly, the sand grains flow in synchrony and set each other vibrating like the membrane on a gigantic loudspeaker. The synchronisation causes the air to move in and out between the grains, creating a powerful sound wave.

G 33 What really surprised the scientists, however, was that they were able to take samples of the singing sand back to France and replicate the sound at ENS, proving that it's the sand, not the dune shape, that causes the sound. Their studies show the grains are a uniform shape, well-rounded from years of striking each other, and that the variations in size affect the tone. Crucially, the grains are coated with a special veneer, which Douady calls 'desert glaze', made from a precise combination of minerals from surrounding rocks including iron, aluminium, manganese, silicon and calcium. The team found that after a month or so, the veneer wore off and the grains lost their 'voice'. 'We managed to reproduce the desert glaze and then the grains started to sing again,' says Douady. 'We tried putting the coating onto different grains, but they weren't round enough and it didn't work. But some American colleagues made some artificial grains and managed to make them sing, after covering them in desert glaze. Douady has now made recordings of dunesong from all over the world which are to be made into a CD.