IELTS Academic Reading Practice Test 7

For more than fifteen hundred years, a web of caravan routes connected China with Central Asia, Persia, India and the Mediterranean world. Today it is known as the Silk Road. The name is usually credited to the German geographer Ferdinand von Richthofen, who used the term Seidenstraße in 1877. Some scholars have since found the phrase in earlier German writing, but there is little doubt that Richthofen's work made it popular. The name is misleading, since there was never a single road but a shifting network of tracks and mountain passes, and silk was only one of many goods carried along it.

Chinese records trace the beginning of regular contact with the west to a diplomatic mission. Around 138 BCE, Emperor Wu of the Han dynasty sent an envoy named Zhang Qian to find the Yuezhi, a people who had been driven westwards by the Xiongnu, a nomadic confederation that raided China's northern frontier, in the hope of forming an alliance against their common enemy. Zhang Qian was captured by the Xiongnu and held for about ten years before he escaped and finally reached the Yuezhi.

By then, however, they had settled in fertile new lands and showed no interest in renewing the war. The mission therefore failed in its original purpose, yet the envoy returned to the Han capital with detailed reports of kingdoms that the Chinese had scarcely known existed. His descriptions of the large, powerful horses of the Ferghana Valley were of particular interest to a state whose armies needed cavalry to fight the nomads.

The routes that developed were shaped by some of the harshest terrain on Earth. Travellers leaving western China faced the Taklamakan Desert, an enormous basin of shifting sand that caravans did not attempt to cross directly. Instead, they followed chains of oasis towns, such as Turpan in the north and Khotan in the south, around its edges. In these places, rivers flowing from the surrounding mountains made agriculture possible. Very few individuals ever travelled the whole distance. Goods were usually passed from one trader to another in a long series of exchanges, with each intermediary taking a profit. As a result, an item could cost many times its original price by the time it reached its final buyer.

Among the most successful of these middlemen were the Sogdians, an Iranian-speaking people whose homeland centred on the cities of Samarkand and Bukhara in what is now Uzbekistan. From roughly the fourth to the eighth centuries CE, Sogdian merchants settled in towns throughout Central Asia and northern China. Their language became a common medium of trade along much of the route. Some of the most vivid evidence of their activities comes from a bundle of letters discovered in 1907 by the archaeologist Aurel Stein in the ruins of a watchtower west of Dunhuang. Dating from the early fourth century, the letters had apparently never reached the people to whom they were addressed. Two of them were written by a woman who had been left behind in Dunhuang with her daughter and who complains bitterly that her husband has abandoned them.

The animal best suited to the task was the Bactrian camel, a two-humped species native to Central Asia that can tolerate both the bitter winters and the scorching summers of the region and can survive for long periods without water. Camels travelled in large caravans, partly for efficiency and partly for protection against bandits. At night, merchants could stay in caravanserais, walled inns built around a central courtyard where animals were sheltered and goods could be stored securely, with rooms for travellers around the sides. Because transport costs were so high, long-distance trade concentrated on items that combined low weight with high value, such as silk, spices, perfumes and precious stones.

Goods moved in both directions. China exported silk above all, along with lacquerware. In return it imported horses, wool, silver vessels and glass from Roman and later Persian workshops, which was highly prized by Chinese buyers. In the Roman Empire, Chinese silk became a fashionable and conspicuous luxury. Its popularity alarmed some Roman moralists. In the early first century CE the Senate attempted to forbid men from wearing silk garments, which were regarded as unmanly, and the writer Pliny the Elder complained that India, China and Arabia together drained the empire of a hundred million sesterces every year.

For centuries, China guarded the secret of silk production, which depended on raising silkworms on mulberry leaves and carefully unwinding the fine thread from their cocoons. According to the Byzantine historian Procopius, it was only around 552 CE that monks arriving from Central Asia smuggled silkworm eggs into Constantinople at the request of the emperor Justinian. Whether or not the story is accurate in every detail, the Byzantine Empire did go on to develop its own silk industry.

The routes also carried beliefs and knowledge. Buddhism travelled from India into Central Asia and China, and the oasis town of Dunhuang became a major religious centre, with hundreds of cave shrines carved into the cliffs nearby. In 1900 a sealed chamber was discovered in one of these caves containing tens of thousands of documents, among them a copy of the Diamond Sutra dated 868 CE, which is considered the world's oldest dated printed book. In 2014, however, UNESCO recognised the historical importance of the network by adding a 5,000-kilometre section of it, stretching from central China to Central Asia, to its World Heritage List.

In a converted warehouse on the edge of a city, rows of lettuces grow on shelves stacked from floor to ceiling, bathed in artificial light. There is no soil, no sunshine and no weather. This is vertical farming, a form of what specialists call controlled-environment agriculture, in which crops are grown indoors in layers and every factor that affects their growth – light, temperature, humidity, carbon dioxide and nutrients – is managed by computer. Supporters argue that such farms could produce fresh food close to where people live, using a fraction of the land and water required by conventional agriculture. Critics reply that the economics rarely add up.

The phrase itself was the title of a 1915 book by the American writer Gilbert Ellis Bailey, although Bailey had something quite different in mind. His concern was with the depth of the soil and with cultivating the ground more thoroughly, and he even recommended the use of explosives to loosen its deeper layers, rather than stacking crops on top of one another. The modern concept owes most to Dickson Despommier, a professor at Columbia University in New York, who at the end of the 1990s set his students the task of designing a farm that could operate inside a skyscraper. Their proposals were never built, but Despommier promoted the idea energetically, and his 2010 book The Vertical Farm brought it to a wide audience.

Most vertical farms do not use soil at all. The commonest method is hydroponics, in which plant roots are supported in an inert material or suspended directly in water containing dissolved nutrients, which is pumped around the system and reused. In aeroponics, a more technically demanding variant, the roots hang in the air inside a closed chamber and are sprayed at regular intervals with a fine mist of nutrient solution, an arrangement that gives them unusually good access to oxygen. A third approach, aquaponics, links plant cultivation to fish farming. Waste produced by the fish is broken down by bacteria into compounds that the plants absorb as fertiliser, and the plants in turn help to clean the water before it returns to the fish tanks.

The advantages of growing food in this way are considerable. Because water is recirculated rather than lost to evaporation or drainage, vertical farms commonly claim to use around 90 to 95 per cent less water than field agriculture for the same crop. Pests find it difficult to enter a sealed building, so chemical pesticides are rarely needed. Production continues throughout the year, unaffected by droughts, floods or frosts. Farms near cities can also deliver produce within hours of picking, reducing transport costs and spoilage. Stacking crops in layers also produces far higher yields per square metre than a field.

None of this would be practical without the light-emitting diode, or LED. Older fluorescent and sodium lamps were expensive to run and produced so much heat that they had to be kept at a distance from the plants. LEDs have become dramatically cheaper and more efficient over the past two decades. Because they emit relatively little heat towards the crop, they can be positioned just above the leaves, allowing the layers to be packed closely together. They can also be tuned to particular wavelengths. Chlorophyll absorbs red and blue light most strongly, so many farms use LEDs concentrated in those parts of the spectrum, which is why their growing rooms often glow an eerie pinkish purple.

The great weakness of vertical farming is energy. A field of lettuces receives its light free of charge from the sun, whereas an indoor farm must pay for all of its light, as well as for the air conditioning needed to remove the heat that lamps and plants produce. Electricity is consequently one of the largest operating costs, alongside labour. It also determines their environmental credentials: a farm powered by electricity generated from coal or gas may have a larger carbon footprint than the conventional agriculture it replaces, while one supplied by renewable sources compares far more favourably. Energy costs further explain why vertical farms grow leafy greens, herbs and a few soft fruits such as strawberries rather than staple crops. A study published in 2020 calculated that wheat grown in a multi-storey indoor facility could in theory produce hundreds of times more grain per hectare of land than a field, but that the energy required would make it far too expensive to compete.

These economic realities caught up with the industry in the early 2020s. Investors had poured very large sums into the sector during the previous decade. When energy prices rose sharply in 2022 and higher interest rates made borrowing more expensive, several prominent firms found themselves in difficulty. AeroFarms, based in New Jersey, filed for bankruptcy protection in 2023 before emerging later that year in a reorganised form. Bowery Farming, once one of the best-funded companies in the sector, announced in late 2024 that it was ceasing operations altogether.

None of this means that vertical farming has no future. The technology makes most sense in places where land and fresh water are scarce and imported food is expensive, such as Singapore and the desert states of the Persian Gulf, and Japan has operated indoor 'plant factories' for decades. Meanwhile, falling prices for solar and wind power may ease the energy problem. The most realistic prospect, many agricultural scientists believe, is that vertical farms will become a valuable complement to conventional agriculture for certain crops, rather than a replacement for it.

In classrooms, offices and homes, reading has moved steadily from paper to screens. Many schools now issue tablets or laptops instead of textbooks, academic journals are consulted almost entirely online, and much of what adults read each day arrives on a phone. To some observers, this transition is simply a matter of convenience: words are words, whatever surface they appear on. To others, it represents a quiet threat to the kind of sustained, attentive reading on which education depends. Both positions, in my view, overlook what the research actually shows, which is more interesting and more useful than either the enthusiasts or the pessimists tend to admit.

Studies conducted in the 1980s, when most people read from bulky monitors with low resolution and flickering displays, regularly found that reading from a screen was slower and more tiring than reading from paper. Reviews of that early literature concluded that the disadvantage was largely a matter of image quality, and it was widely assumed that the problem would disappear once display technology improved. Modern screens are sharp, bright and stable, and in terms of sheer legibility they are now at least the equal of a printed page.

Yet the gap has not disappeared. In 2018 a team of researchers from Spain and Israel led by Pablo Delgado published a meta-analysis that combined the results of 54 studies conducted between 2000 and 2017, involving more than 170,000 participants in total. Overall, people who read on paper understood texts better than those who read the same material on screens. The effect was modest in size, but it was consistent, and it had several revealing features. It appeared with informational texts but not with narratives, and it was larger when readers had to work under time pressure. Most strikingly, the advantage of paper did not shrink over the period studied, as improvements in technology might have led one to expect; it grew. Nor did younger participants read any better on screens than older ones.

A separate review by Virginia Clinton, published the following year, reached similar conclusions after analysing 33 studies. It found that readers spent roughly the same amount of time on each medium, which suggests that screen readers were not simply rushing. However, it also found that people reading from screens were worse at judging how well they had understood the material. This problem of calibration had been identified earlier by the Israeli psychologists Rakefet Ackerman and Morris Goldsmith, whose 2011 experiments showed that students who studied texts on a screen tended to be overconfident about how much they had learnt. When the students could decide for themselves how long to study, those reading on screen spent less time and performed worse; when the study time was fixed, the difference in performance largely vanished.

What could explain these findings? One possibility concerns the physical character of the printed book. Readers of paper can feel the thickness of the pages on either side, and they often remember where on a page a particular passage appeared, which may help them to build a mental map of the text. In one study led by the Norwegian reading researcher Anne Mangen, people who read a short mystery story on an e-reader were less accurate than those who read a paperback edition when asked to put events from the plot in the correct order. A second explanation, sometimes called the shallowing hypothesis, holds that the problem lies less in the device than in the habits associated with it. Because most of what we read on screens consists of messages, headlines and social media posts, we may have learnt to approach any text on a screen with the rapid, skimming attitude that such material invites.

I find the second explanation the more persuasive of the two, not least because it accounts for the curious detail that the paper advantage has increased over time. If screens were inherently worse for reading, the gap should have narrowed as they improved. If, on the other hand, the gap reflects a mental habit, its growth is exactly what one would predict as people spend ever more of their lives skimming digital content. The distinction matters, because a habit, unlike a property of glass and pixels, can in principle be changed. Indeed, some experiments have found that simple interventions, such as asking readers to generate keywords or to summarise what they have just read, reduce or even remove the disadvantage of screens.

This does not mean that the concerns of critics such as the cognitive neuroscientist Maryanne Wolf, whose 2018 book Reader, Come Home warns that digital reading may erode our capacity for deep, reflective attention, can be dismissed. Nor, however, does it mean that schools should abandon digital materials, which offer real advantages in cost, accessibility and the ease with which they can be updated. What the evidence suggests is a more careful approach. For difficult informational texts, especially when the stakes are high, paper remains the safer choice for now. At the same time, students should be taught explicitly how to read demanding material on screens – slowing down, checking their own understanding and resisting the pull towards skimming – since this is how they will read for most of their lives.

The debate over paper and screens is often presented as a contest between the old and the new, in which one side must eventually win. The evidence points to something different. The medium does matter, but mainly because of what we have learnt to do with it.