IELTS Academic Reading Practice Test 8

Glass is one of the few materials that humans used in its natural form long before they learnt to make it. Obsidian, a black volcanic glass that forms when lava cools too quickly for crystals to develop, was prized in prehistoric times because it could be chipped into blades sharper than any metal. That rapid cooling explains what makes glass unusual. In most solids, atoms are arranged in a regular, repeating pattern, but in glass they are frozen in the disordered arrangement of a liquid. The result is a material that is rigid yet has no crystal structure.

According to a story told by the Roman writer Pliny the Elder, glass was discovered by accident when merchants carrying natron, a naturally occurring form of soda, rested their cooking pots on blocks of it beside a beach fire and found streams of glass flowing from the melted sand. Historians regard the tale as a legend. The earliest manufactured glass objects are in fact beads from Mesopotamia, made more than four thousand years ago. Glass vessels appeared in Mesopotamia and Egypt by the middle of the second millennium BCE. They were made by covering a core of clay and dung, attached to a metal rod, with molten glass, and then scraping the core out once the glass had cooled. Such vessels usually held perfumes or oils and were luxury items.

The basic chemistry has changed little since. The main ingredient is silica, usually in the form of sand, but pure silica melts only at around 1,700 degrees Celsius, far beyond the reach of ancient furnaces. Glassmakers therefore added a flux, a substance that lowers the melting point. Around the Mediterranean this was usually natron from Egyptian lake deposits, while elsewhere the ashes of certain plants were used. A third ingredient, lime, acts as a stabiliser. Without it, glass made from silica and soda would slowly dissolve in water. Colour could be controlled by adding small quantities of metal compounds; cobalt, for example, produces a deep blue. Most glass produced today, from bottles to windows, is still of this basic soda-lime type.

The most important innovation in the history of the craft came in the first century BCE, somewhere on the eastern coast of the Mediterranean. Craftsmen discovered that a blob of molten glass on the end of a hollow tube could be inflated by blowing into it, rather like a balloon, and then shaped with simple tools while it was still soft. Glassblowing was far faster than earlier methods. Within a few generations, workshops throughout the Roman Empire were producing cups, jugs and bottles so cheaply that glass, once a luxury, became an everyday material for ordinary households.

After the collapse of the western Roman Empire, the most celebrated glass in Europe came from Venice. In 1291 the city's authorities ordered most glass furnaces to move to the nearby island of Murano, partly to reduce the risk of fire in the crowded city. The glassmakers enjoyed high social status, but they were forbidden to leave the republic, since the state was determined to protect the secrets of their trade. In the fifteenth century, Angelo Barovier is credited with developing cristallo, a glass of exceptional clarity named after rock crystal, which was made by carefully purifying the raw materials. Venetian glass went on to dominate European luxury markets for around two hundred years.

That dominance was eventually challenged from England. In the 1670s George Ravenscroft began adding lead oxide to his glass mixture, producing a heavy, brilliant material that bent light strongly and was soft enough to be cut and engraved with elaborate patterns. Lead glass, often known simply as crystal, became fashionable for tableware, and its optical qualities later made it valuable for the manufacture of lenses.

Windows posed a different problem, because they required flat sheets. In the crown method, a glassblower inflated a bubble, transferred it to a solid iron rod and spun it rapidly until it opened out into a wide disc, which was then cut into panes. In the cylinder method, a long cylinder was blown, split along its length and flattened while still soft. Both techniques produced glass of uneven thickness.

This, rather than any slow flow of the material over the centuries, is why panes in some old buildings are thicker at the bottom, although the opposite explanation is often repeated. The cylinder method was improved during the nineteenth century, and nearly 300,000 panes made in this way were used in the Crystal Palace, built in London for the Great Exhibition of 1851.

Mechanisation transformed the industry in the twentieth century. In the early 1900s the American inventor Michael Owens developed a machine that could make glass bottles automatically, and within a few decades hand-blown bottles had become largely obsolete. Flat glass was revolutionised by the float process, announced in 1959 by the British firm Pilkington after years of development led by Alastair Pilkington. Molten glass is poured onto a bath of molten tin, on which it spreads out to form a perfectly level sheet. Because both surfaces are already smooth as the glass cools, the expensive grinding and polishing previously required are no longer necessary, and most of the world's flat glass is now made in this way.

Every autumn, millions of monarch butterflies leave their breeding grounds in southern Canada and the eastern United States and fly south to a handful of mountain forests in central Mexico. For some individuals the journey is around 4,000 kilometres long, an astonishing distance for an insect weighing about half a gram. What makes the migration truly remarkable, however, is that none of the butterflies that set out has ever made the trip before. They are several generations removed from the ancestors that left Mexico the previous spring, yet they arrive at the same small patches of forest year after year. Biologists regard it as one of the most spectacular insect migrations on the planet.

Where exactly the eastern monarchs spent the winter remained a mystery to scientists until the 1970s. The zoologist Fred Urquhart of the University of Toronto spent decades trying to solve it, recruiting volunteers across North America to attach small numbered labels to the wings of butterflies and to report any that were recovered. The breakthrough came in January 1975, when Kenneth Brugger and Catalina Aguado, who were working with Urquhart, located an immense colony on a mountainside west of Mexico City. When Urquhart visited the site the following year, he found among the millions of butterflies one bearing a tag that had been attached in the United States.

The overwintering sites lie at altitudes of around 3,000 metres in forests of oyamel fir. Conditions there are almost ideal for a butterfly that must survive several months without breeding. The air is cool enough to slow the insects' metabolism, allowing them to conserve the fat reserves they built up on the journey south, yet the dense forest canopy acts like a blanket, protecting them from the most severe frosts. The butterflies gather in clusters so dense that branches bend under their weight, and a single colony may contain many millions of individuals. A separate population living west of the Rocky Mountains follows a shorter route, spending the winter in groves of trees along the coast of California.

The migration depends on an unusual life cycle. Monarchs born in spring and early summer live for only a few weeks as adults, long enough to mate and lay eggs. The generation that emerges in late summer is different. Triggered by shortening days and falling temperatures, these butterflies delay reproduction and can live for up to eight months, which is long enough to fly to Mexico, survive the winter and begin the return journey. In spring they mate and fly north to the southern United States, where they lay their eggs and die. Their offspring, and the generations that follow, then continue northwards, so that the full round trip spans several generations.

How do butterflies that have never made the journey find their way? Much of the answer lies in a sun compass. Monarchs use the position of the sun to maintain a south-westerly heading, but because the sun's position shifts steadily from hour to hour, they need an internal clock to compensate for that change. In 2009 a team led by the neurobiologist Steven Reppert reported that a crucial part of this timekeeping takes place in the antennae: butterflies whose antennae had been painted black could no longer orient themselves correctly. Later work by the same group showed that monarchs can also sense the Earth's magnetic field, which may help them to navigate when the sun is hidden by cloud.

The monarch's survival also depends on a single group of plants. Its caterpillars feed only on milkweeds, which contain chemicals called cardenolides that are poisonous to many animals. The caterpillars are able to store these compounds in their bodies, and the compounds remain in the adult butterflies, making them toxic to birds. The bright orange and black wings serve as a warning: a bird that has eaten a monarch and been sick is likely to avoid them in future. This dependence on milkweed, however, also makes the species vulnerable when the plants disappear.

And disappear they have. The area of forest occupied by monarchs in Mexico, which researchers measure each winter as an indicator of population size, reached a peak of about 18 hectares in 1996–97 but fell to less than one hectare in 2013–14. Several factors appear to be responsible. In the agricultural Midwest of the United States, the widespread use of herbicides on crops genetically engineered to tolerate them has removed much of the milkweed that once grew among the fields. In Mexico, illegal logging damaged parts of the overwintering forests, although it has since been greatly reduced. Severe storms, droughts and heatwaves, which are expected to become more frequent as the climate warms, add further pressure.

Efforts to reverse the decline are taking place at every scale. Much of the overwintering area has been protected since the 1980s, and in 2008 it was designated a UNESCO World Heritage Site. In North America, government agencies, farmers and private gardeners have been encouraged to plant milkweed and nectar-producing flowers along roadsides and in parks and gardens. Volunteers continue to tag butterflies through programmes such as Monarch Watch, helping scientists to track the migration. In December 2024 the United States Fish and Wildlife Service proposed listing the monarch as a threatened species, a step that would give it legal protection.

Few ideas have spread through education as quickly as gamification, the use of elements borrowed from games, such as points, badges, levels and leaderboards, in activities that are not themselves games. The word seems to have been coined in the early 2000s, but it became fashionable only around 2010, when software designers and marketing departments began adding game features to everything from fitness apps to customer loyalty schemes. Schools and universities soon followed. Language-learning apps reward daily practice with unbroken streaks, quiz platforms turn revision into a contest, and teachers award digital badges for completed tasks. The appeal is obvious: games are enormously engaging, and learning often is not.

It is worth being precise about what gamification is not. It differs from game-based learning, in which students play a complete game designed to teach particular content, such as a simulation of an ecosystem or a strategy game set in a historical period. Gamification leaves the underlying activity unchanged and adds a layer of rewards and feedback on top of it. The distinction matters, because the criticisms that apply to one approach do not necessarily apply to the other, and much of the confusion in public debate arises from treating the two as if they were the same thing.

So does gamification work? The most thorough answer so far comes from a meta-analysis by the educational psychologists Michael Sailer and Lisa Homner, published in 2020, which combined the results of experimental studies of gamified learning. They found small positive effects on three kinds of outcome: what students learnt, how motivated they were, and how they behaved, for instance how actively they took part. Only the effect on learning itself, however, remained robust when the analysis was limited to the most rigorously designed studies. The effects on motivation and behaviour were less stable, which suggests that some of the enthusiasm generated by early research reflected weaknesses in the way that research was conducted.

Some studies have found that gamification can even backfire. In a semester-long experiment published in 2015, the communication researchers Michael Hanus and Jesse Fox compared two versions of the same university course, one of which included badges, a leaderboard and a virtual currency. Over time, students in the gamified version reported lower intrinsic motivation and satisfaction, and they also achieved lower scores in the final examination. The researchers suggested that constant comparison with classmates on the leaderboard may have discouraged students who found themselves near the bottom of it.

Such findings would not have surprised psychologists who study motivation. As early as 1971, Edward Deci reported that people who were paid for solving puzzles subsequently spent less of their free time on them than people who had not been paid. Two years later, Mark Lepper, David Greene and Richard Nisbett found that young children who had been promised a certificate for drawing later showed less interest in drawing than children who had received no reward, or who had been rewarded unexpectedly. A 1999 review of more than a hundred experiments, led by Deci, concluded that expected, tangible rewards tend to undermine people's interest in activities that they already find enjoyable.

This does not mean that rewards are harmful in themselves. Deci and his colleague Richard Ryan went on to develop self-determination theory, which proposes that people are most strongly motivated when they feel a sense of autonomy, competence and connection with others. From this perspective, what matters is whether a reward is experienced as controlling or as informative. A badge that tells a student she has mastered a difficult skill may strengthen her sense of competence, whereas one used to pressure her into completing tasks may weaken her sense that she is acting by choice.

In my view, the lesson from this research is not that gamification should be abandoned but that its most visible features are often its least valuable. Points, badges and leaderboards are the easiest elements of games to copy, which is precisely why they are so widely used. Yet they are not what makes good games absorbing. Players persist with difficult games because the challenges are carefully matched to their growing skill, because they receive immediate and informative feedback, and because failure carries little penalty and simply invites another attempt. These are also, as it happens, the features of effective teaching.

There is a further risk in the way rewards are used. When a badge is awarded simply for logging in or for completing a fixed number of exercises, students may learn to pursue the badge rather than the understanding it was meant to represent. In 2012 the technology research firm Gartner predicted that around 80 per cent of the gamified applications then in use would fail to meet their objectives by 2014, mainly because of poor design. Education is not a business, but the warning applies to it: a reward system that encourages students to find shortcuts is worse than no system at all.

None of this means that teachers should avoid game elements altogether. A short competitive quiz can enliven a lesson, and a visible record of progress can encourage a student who has lost confidence. But gamification works best as a modest addition to good teaching rather than as a substitute for it. The question to ask is not whether an activity looks like a game, but whether it gives learners the challenge, the feedback and the freedom to fail that make games worth playing in the first place.