IELTS Academic Reading Practice Test 78

Before the late eighteenth century, almost every region of Europe had its own units of length, weight and volume. A 'foot' in one town might be several centimetres shorter than a 'foot' in the next, and the same word could refer to different quantities depending on the commodity being measured. This local variety was not merely an inconvenience for traders; it also made fraud easier and scientific communication almost impossible. As manufacturing and long-distance commerce expanded, pressure grew for a single set of measures that could be understood everywhere.

The French Revolution provided the political opportunity to introduce such a system. In 1790, the National Assembly asked the French Academy of Sciences to devise a universal system of weights and measures. The Academy appointed a commission of leading scientists, who recommended a decimal system based on natural standards rather than on the length of a king's arm or the weight of a particular grain. Decimalisation meant that units would be multiplied or divided by powers of ten, which would make calculation far simpler than working with the old units, many of which were based on twelves, sixteens or other awkward multiples.

The commission proposed that the unit of length should be one ten-millionth of the distance from the North Pole to the equator along the meridian passing through Paris. This unit was named the metre. To establish its exact length, two astronomers, Jean-Baptiste Delambre and Pierre Méchain, spent six years measuring the meridian between Dunkirk and Barcelona, a task made hazardous by the political turmoil of the revolutionary period. Their result was used to create a platinum bar that became the official standard metre in 1799. Although later measurements showed that the bar was very slightly too short, the principle of a unit derived from the Earth remained.

For the unit of mass, the commission chose the gram, defined as the mass of one cubic centimetre of pure water at its freezing point. This was also an attempt to base the units on nature, since water was available everywhere and its properties could be checked by anyone. In 1799, a practical standard was made in the form of a platinum cylinder weighing one kilogram, and this object, known as the Kilogram of the Archives, served as the reference for over eighty years. The litre was defined as the volume of one kilogram of water at its maximum density, which occurs at about four degrees Celsius.

The new system, which came to be known as the metric system, was not instantly accepted even in France. Napoleon later allowed some traditional units to return, but the metric system was gradually taught in schools and used by government departments, so that by the mid-nineteenth century it had become firmly established in French life. Its advantages were evident: calculations involving money, land and goods became much easier, and the system could be extended to new quantities as science advanced.

Other countries adopted the metric system at different speeds. The Netherlands and Belgium did so in the 1820s, and in 1875 an international treaty known as the Metre Convention was signed in Paris by seventeen nations. This treaty created the International Bureau of Weights and Measures (BIPM) and the General Conference on Weights and Measures (CGPM), which together maintain the international standards and decide on changes. The original platinum metre and kilogram bars were then replaced by more stable platinum-iridium copies kept under carefully controlled conditions.

Over the following century, the metric system expanded to cover additional physical quantities. The units for electric current, temperature and luminous intensity were added, and in 1960 the whole system was formally renamed the International System of Units, universally known as the SI. By this time, the metre had been redefined using the wavelength of light, and later the speed of light in a vacuum was adopted as the basis for the metre. Such redefinitions meant that the units no longer depended on physical objects that could change over time.

The most significant recent change came in 2019, when the kilogram was redefined by fixing the numerical value of the Planck constant, a fundamental quantity in quantum physics. For the first time, all seven base units of the SI were based on constants of nature rather than on artefacts. This meant that the kilogram no longer depended on a small metal cylinder kept in a vault near Paris, but could in principle be realised in any well-equipped laboratory.

Today, the metric system is the official system of measurement in almost every country. A few nations, most notably the United States, have not adopted it for everyday use, although even they use metric units in science, medicine and international trade. The United Kingdom retains some imperial units for road signs and beer, while Myanmar and Liberia have also been slow to change. Nevertheless, the metre, the kilogram and the litre are now so familiar that it is easy to forget how recently and how deliberately they were created.

For more than a century after the discovery of Archaeopteryx in the 1860s, feathers were thought to be unique to birds. This small fossil, which lived around 150 million years ago, showed a mosaic of bird-like and reptilian features, including well-developed flight feathers. Because no other creatures were known to have feathers, palaeontologists assumed that feathers had evolved for flight, and that their presence in Archaeopteryx was simply evidence that it was a bird. The idea that dinosaurs might have had feathers was rarely considered, and when it was, it was usually dismissed.

That view changed dramatically in the 1990s, when a series of spectacular fossils began to emerge from Liaoning Province in north-eastern China. The volcanic ash deposits there preserved soft tissues in exceptional detail, including impressions of what appeared to be simple feathers. In 1996, scientists described Sinosauropteryx, a small predatory dinosaur covered in a coat of hair-like filaments. These filaments were not complex feathers, but they were clearly integumentary structures, suggesting that feather-like coverings had evolved in non-avian dinosaurs long before the origin of birds. Soon afterwards, other remarkable specimens were announced. Caudipteryx and Protarchaeopteryx, for example, possessed fully formed feathers with a central shaft, while Beipiaosaurus, a member of a very different dinosaur group, also carried filamentous structures. Together these finds made it impossible to regard feathers as a bird-only feature.

Since then, many more feathered dinosaur species have been identified, and their feathers show a wide range of forms. Some, like those of Caudipteryx, were short and symmetrical, with a central shaft and branching barbs, but they were not suitable for flight. Others, such as the long feathers on the arms and legs of Microraptor, formed airfoils that could have allowed gliding or even powered flight. The large tyrannosauroid Yutyrannus, which grew to about nine metres long, was covered in long filamentous feathers, demonstrating that even very large dinosaurs could be feathered. The feathers vary from flexible, unbranched filaments to stiff, pennaceous feathers with a closed vane. Some species, including a small creature named Epidexipteryx, had long ribbon-like tail feathers that were clearly not suited to flight and were probably used for display.

The discovery of feathers on dinosaurs that could not fly forced scientists to reconsider the original function of feathers. Flight could not have been the reason feathers first appeared, because the earliest feathered dinosaurs were ground-dwelling animals with no aerodynamic ability. Instead, researchers proposed that feathers initially evolved for insulation, helping small active dinosaurs to maintain a high body temperature. This hypothesis is consistent with the fact that the earliest feathers are simple filaments, similar to the down of modern birds, which is effective at trapping air and reducing heat loss.

Other functions may have followed. Some dinosaurs had feathers with colour patterns, and the presence of melanosomes—pigment-bearing structures—in fossil feathers has allowed scientists to reconstruct the colours of some species. For example, Sinosauropteryx appears to have had a reddish-brown and white banded tail, while Anchiornis, a small feathered dinosaur, had black and white wings with a red crest. Such colour patterns suggest that feathers were also used for display, either to attract mates or to signal to rivals.

The fossil record also shows a gradual transition from simple filaments to complex flight feathers. Early feathers were unbranched or weakly branched, but later forms developed a central rachis, barbs and barbules that interlocked to create a continuous surface. These changes allowed feathers to become stiff and aerodynamic, enabling them to generate lift. Once flight feathers had evolved, natural selection could refine them for ever more efficient flying, but the initial steps in feather evolution were probably driven by thermoregulation and display, not by the need to fly. Biologists have proposed a staged model for this transition. A simple hollow filament gave way to a tuft of filaments, then to a central shaft with branches, and finally to the closed vaned feather of modern birds, with barbs held together by tiny hooks on smaller branches called barbules. Each stage can be seen in the fossil record, although not always in a single lineage.

Some researchers have suggested that feathers may have first appeared even earlier, in the common ancestor of dinosaurs and pterosaurs, because simple filamentous structures have been found in some pterosaur fossils. However, this idea remains controversial, since the filaments in pterosaurs may be made of a different material. Feathers are now known from a wide variety of coelurosaurs, the subgroup of theropods that includes tyrannosaurs, dromaeosaurs and birds. What is now beyond doubt is that feathers were widespread among theropod dinosaurs, the group that includes birds, and that many non-avian dinosaurs were feathered. The old distinction between 'feathered birds' and 'scaly reptiles' has been permanently erased.

The study of feathered dinosaurs has transformed our understanding of the origin of birds. Rather than appearing suddenly, the defining features of birds—feathers, a wishbone and hollow bones—were assembled gradually over millions of years within the dinosaur lineage. Feathers, once thought to be the exclusive badge of birds, are now recognised as a much older innovation, one that appeared long before the first bird took to the air. Indeed, birds are now classified simply as a lineage of feathered theropod dinosaurs, and the distinction between dinosaur and bird has lost much of its former clarity.

Heritage tourism—travel that focuses on historic sites, monuments, museums and cultural traditions—has become one of the fastest-growing sectors of the global travel industry. Millions of people each year visit places such as the Pyramids of Giza, the Forbidden City in Beijing, and the ancient Inca citadel of Machu Picchu. This growth is often welcomed, because tourists bring money that can be used to restore crumbling buildings and support local economies. Yet the very popularity of these places also creates problems that can undermine the heritage they are meant to celebrate.

The economic argument for heritage tourism is straightforward. Visitors spend money on accommodation, food, guides and souvenirs, and this spending creates jobs and tax revenue. In many regions, particularly in developing countries, heritage tourism is seen as a relatively clean way to generate income without the pollution associated with heavy industry. Historic town centres that were once neglected have been revitalised, and some traditional crafts have been saved from extinction because tourists provide a market for them.

However, the influx of visitors can place enormous strain on physical structures. The foot traffic of thousands of people a day wears away stone steps, damages fragile floors and disturbs the microclimate of enclosed spaces. In some famous caves and tombs, the moisture and carbon dioxide from visitors' breath have caused mould to grow on ancient paintings. Attempts to manage this, such as limiting the number of visitors per day or closing parts of a site, often meet resistance from tour operators who depend on unrestricted access.

A further problem is the displacement of local residents. As heritage tourism expands, property prices and rents rise, and traditional shops are replaced by souvenir outlets and chain restaurants. In old city centres, the people who once lived there are pushed out, and the place becomes a stage set rather than a living community. This process, sometimes called 'tourism gentrification', has been documented in cities around the world, from Venice to Prague to Quito. The irony is that the very atmosphere that attracts tourists—the daily life of a historic neighbourhood—is destroyed by their arrival.

There is also the question of authenticity. To cater to tourist expectations, local traditions may be simplified or commercialised. A ritual that once took place at a particular season may be performed weekly for paying audiences, and crafts that were once made for practical use are mass-produced as trinkets. Some critics argue that heritage tourism inevitably turns living culture into a commodity, stripping it of its original meaning. Others respond that all cultures change over time, and that tourism can encourage communities to take pride in traditions they might otherwise abandon.

Another concern is the environmental impact of large numbers of visitors. Many heritage sites are located in fragile ecosystems, such as high mountain regions, coral reefs or wetlands. The construction of airports, roads and hotels to serve tourists can destroy the very landscapes that make a site attractive. Cruise ships bring thousands of passengers to small coastal towns, overwhelming local infrastructure and discharging waste into the sea. In some cases, the carbon footprint of flying to a distant heritage site may exceed any local environmental benefit.

Despite these problems, I do not believe that heritage tourism should be abandoned. Well-managed tourism can provide the funds needed to conserve sites that would otherwise deteriorate through lack of resources. It can also foster international understanding by exposing people to the achievements and traditions of other cultures. The issue is not whether tourists should come, but how they should come, how many should come, and who should benefit from their visit.

In my view, the key is to involve local communities in decisions about tourism development. When residents have a stake in the management of a heritage site, they are more likely to protect it and to ensure that the benefits are shared fairly. This might mean limiting visitor numbers, raising prices for foreign tourists, or channelling revenue directly into conservation and community projects. Such measures are not popular with everyone, but they are essential if heritage tourism is to be sustainable in the long term.

There are examples of successful approaches. The Galápagos Islands, for instance, have strict limits on visitor numbers and require licensed guides, and the revenue helps fund the national park. Some Italian cities have introduced entry fees for day-trippers to reduce overcrowding. These policies show that it is possible to balance the economic value of tourism with the need to protect heritage. The challenge is to extend such practices more widely, rather than allowing the market to dictate how many visitors a site can absorb.

Ultimately, heritage tourism is neither inherently good nor inherently bad. Its effects depend on how it is planned and governed. If we treat heritage sites merely as products to be sold, we will destroy the very things we claim to value. If, on the other hand, we treat them as living assets that belong to their communities and to humanity as a whole, tourism can become a force for conservation and mutual respect. The choice is ours to make.