IELTS Academic Reading Practice Test 469

Between roughly AD 100 and 800, the desert coast of northern Peru was home to one of the most accomplished societies of the ancient Americas. The Moche built huge platforms of mud brick, cut canals across a landscape that receives almost no rain, and made pottery that is still admired for its realism and technical skill. They left no writing that anyone has been able to read, so nearly everything known about them has been pieced together from excavation. Even their name is a modern invention, taken from the valley where the first large ruins were examined; nobody knows what these people called themselves.

Their world was shaped by water. Although the coast is one of the driest deserts on earth, dozens of short rivers run down from the Andes to the Pacific, and each supported a cluster of villages and fields. Farmers learned to divert these rivers into canals, some several kilometres long, which carried water to plots of maize, beans, squash and peanuts. A canal that silts up quickly fails, so the system required constant maintenance. Keeping the channels clear also demanded cooperation between neighbouring communities, and disputes over water were probably frequent. Control of the supply may in turn have underpinned the authority of local leaders, whose monuments required a great many people to be fed.

The largest surviving monument is the Huaca del Sol, a stepped platform in the Moche valley built from millions of sun-dried adobe bricks. Many of the bricks carry a mark, apparently identifying the group of workers who made them. Beside the platform stands the Huaca de la Luna, whose walls preserve painted friezes in red, yellow, black and white, showing a fanged deity and repeated images of captives. The Huaca del Sol was badly damaged in the seventeenth century, when Spanish treasure hunters diverted the river to wash away part of the mound in the hope of finding gold.

Moche pottery is the richest source of evidence about daily life, because the desert preserves it in enormous quantities. Potters are best known for vessels with a stirrup-shaped spout, a tube that rises from the body of the pot and loops back to form a handle. Yet they also modelled faces, animals, plants, houses and tools with great accuracy, and some vessels are painted with scenes of hunting, fishing, weaving and fighting. Fine lines, applied with a brush made from a few hairs, record details of dress and ornament that would otherwise have been lost.

For a long time the Moche were known mainly through such objects, since almost every tomb was looted soon after it was found. That changed in 1987, when looters digging into a platform at Huaca Rajada in the Lambayeque valley began selling gold ornaments, and police recovered some of what they had taken. The archaeologist Walter Alva, then director of a regional museum, started an excavation and uncovered a burial that had escaped the robbers. The dead man, soon known as the Lord of Sipán, had been buried with ornaments of gold and silver, bead necklaces and hundreds of other objects. The discovery transformed understanding of Moche wealth and craftsmanship.

Moche art makes it plain that warfare and sacrifice were central to public life. Painted scenes show battles between groups of warriors, the capture of prisoners, and a ceremony in which captives, stripped of their weapons and clothing, are presented to a figure in elaborate regalia. Their blood was then collected in a cup and offered to the deity. Excavation has supported these images. In one plaza at the Huaca de la Luna, archaeologists found the skeletons of more than seventy young men, many with cut marks on their bones. They interpreted the deposit as the remains of a single sacrificial event.

The end of Moche dominance was not a single event. From about AD 600 the archaeological record in the southern valleys changes: some sites show thick layers of flood sediment, while others contain evidence of a long dry period. A particularly severe El Niño is one candidate for the damage, and a drought lasting decades is another. That periodic warming of the eastern Pacific disrupts weather along the coast and can bring both heavy rain and prolonged dry spells. Others argue that the collapse was political, pointing to conflict within communities and to the growth of a new centre further north. Whatever the mixture of causes, the great southern settlements were abandoned within a few generations.

Excavation has also overturned old assumptions about who held power. In 2005, at the site of El Brujo, archaeologists opened a tomb containing the body of a young woman covered in tattoos of spiders and snakes. She had been buried with gold ornaments, weapons and a sacrificed companion. Dating placed the burial in the fifth century AD, and its richness made it clear that high status was not restricted to men. Other finds have complicated any simple picture of Moche society.

Today the mud-brick pyramids are steadily eroding. Rain is rare in normal years, but the heavy rainfall that comes with a strong El Niño dissolves exposed surfaces, and illegal digging continues in remote valleys. At the Huaca de la Luna, teams have built roofs over the painted walls and consolidated the adobe beneath them. The study of the Moche has become increasingly international, and every season of excavation produces fresh evidence against which earlier interpretations must be tested.

Hail is ice that falls from thunderstorms, and it is easily confused with other kinds of frozen precipitation. Sleet, in the sense used in North America, consists of raindrops that freeze into small, translucent pellets on their way down; in Britain the same word means a mixture of rain and partly melted snow. Snow forms when water vapour turns directly into ice crystals. Hail is different in scale and in origin. A hailstone is a lump of ice, sometimes larger than a tennis ball, that has grown inside a towering cloud by collecting water that was still liquid well below the freezing point. It often falls in summer, on days when the ground is warm and the air near the surface is hot.

To make hail, a cloud must be deep and violent. The cumulonimbus cloud that produces thunderstorms forms where warm, moist air near the ground is unstable and rises rapidly, cooling as it goes. As the air ascends, its water vapour condenses, releasing heat that makes it rise faster still, so that a strong upward current of air — the updraft — develops inside the cloud. In a big storm this current may extend ten kilometres or more above the ground, far above the level at which the temperature falls below zero. The stronger the updraft, the more water it can carry upwards and the longer ice particles can remain inside the cloud.

High in the cloud, where the temperature may be thirty degrees below zero, water does not always freeze. Tiny droplets can remain liquid in a supercooled state until they touch a particle on which ice can form, such as a speck of dust, a sea-salt crystal or a fragment of ice already present. When that happens, the droplet freezes almost instantly. A mass of ice that tumbles through this region collects such droplets and becomes a small, opaque pellet known as graupel, a few millimetres across. This pellet, the embryo of the future hailstone, is the starting point of everything that follows.

Once an embryo exists, it grows by sweeping up supercooled droplets, which spread over its surface and freeze. How the ice looks depends on how quickly this happens. If the stone passes through a region rich in liquid water, the water freezes slowly enough for air bubbles to escape, producing clear ice. If it meets only a little water, the droplets freeze at once and trap air, producing white, opaque ice. The alternation of clear and cloudy bands, visible when a large hailstone is cut in half, is therefore a record of the different parts of the cloud the stone travelled through before it fell.

None of this would matter if the stone simply dropped out of the cloud. What keeps it inside is the balance between the strength of the updraft and the speed at which the stone falls. A hailstone a centimetre across falls at perhaps ten metres a second. One the size of a golf ball may be travelling at close to a hundred kilometres an hour by the time it reaches the ground. Only a storm with an exceptionally powerful updraft can hold such stones aloft. The largest authenticated hailstone, measured after a storm in South Dakota in 2010, was about twenty centimetres across, roughly the size of a melon.

Hail is not evenly distributed. It is most frequent in the interior of continents at middle latitudes, where warm, humid air from the south meets colder air from the north and the land surface heats strongly in summer. The high plains of the United States, from Texas northwards into Nebraska and the Dakotas, receive more large hail than almost anywhere else on earth. Mountainous regions such as the Himalayas and parts of the Alps also report frequent falls. Storms that produce hail usually do so in the afternoon and evening, when the ground is warmest and rising air is strongest, and the season peaks in late spring and early summer. Hailstones are sometimes carried sideways by strong winds and may land far from the storm that produced them.

Because hailstones melt quickly and a storm may pass in half an hour, much of the evidence is collected on the ground. A long-established instrument is the hailpad, a sheet of insulating board wrapped in kitchen foil and laid out in a field. Each stone that hits it leaves a dent whose width gives the size of the stone, so a network of pads shows how hail varies across a region. Weather radar offers a wider view, since a zone of unusually strong reflectivity in a storm often indicates large ice particles. Damage surveys, which record shattered roof tiles, dented car panels and shredded crops, complete the picture, and photographs sent by members of the public now arrive within minutes.

Much remains uncertain. Why one storm produces hail and a very similar one does not is still poorly understood, which is one reason forecasts of hail remain less reliable than forecasts of rain. Attempts to reduce hail by seeding clouds with particles intended to create more, smaller ice crystals have been made in many countries since the middle of the twentieth century, but no method has been shown to work consistently. Climate change adds a further puzzle: a warmer atmosphere can hold more moisture and produce stronger updrafts, which might allow bigger stones to grow, while a higher freezing level might reduce the number of storms that produce hail at all.

Twenty years ago nobody could say which was the best university in the world, because no one had attempted a single league table covering institutions in different countries. That changed in 2003, when a team at Shanghai Jiao Tong University published the Academic Ranking of World Universities, an exercise designed originally to show how far Chinese universities lagged behind the strongest institutions elsewhere. A commercial global ranking appeared the following year, and newspapers and magazines in many countries began to publish annual tables. Rankings are now consulted by governments, by employers and by families choosing where to apply, and a university's place in them has become, for some institutions, a part of their identity. Employers have been drawn in as well: some large firms publish lists of the universities from which they recruit.

Most of these tables are built from a narrow set of indicators. The number of articles a university's staff publish in international journals, and the number of times those articles are later cited by other researchers, carry heavy weight. So does the tally of major awards held by staff and former students. Questionnaires asking academics to name the institutions they most admire supply much of what remains. Direct evidence about teaching is almost entirely absent, because there is no agreed method of comparing what students learn in different countries. The result is a method that favours large institutions with medical schools and strong science departments, and it also suits universities in English-speaking countries, whose journals dominate the databases the compilers search.

Because the tables are read by people who allocate money and status, universities have reorganised themselves around them. Institutions have recruited professors with exceptional citation records, set staff publication targets, opened programmes taught in English to attract overseas students and, in some cases, closed departments that bring little credit. Critics describe this as mission drift: a process in which institutions founded to serve a region, or to train teachers and nurses, come to resemble one another in pursuit of a higher position. The pressure is greatest where funding is already tight, since a fall of a few places may be reported as a decline in national standing.

The figures themselves are not always trustworthy. Where citation counts matter, some authors and editors have arranged to cite one another's work. A few institutions have been found to have inflated their records by employing highly cited researchers on part-time contracts and counting them as full-time staff. Reputation surveys, which rest on the impressions of academics who cannot know thousands of institutions in detail, are particularly easy to influence through advertising and alumni campaigns. Some universities have concluded that the game is not worth playing and no longer supply data, while others dispute published figures and demand corrections. Errors, when they occur, tend to be noticed by the institutions concerned rather than by the compilers.

Defenders of the rankings make a straightforward case. Before 2003 there was no comparable information about universities across borders, and judgements about quality rested on reputation and anecdote. The tables compelled institutions to publish data, exposed differences that had been hidden and gave the public a means of holding universities to account. Supporters acknowledge that the measures are imperfect, but argue that a rough comparison is better than none, and that criticism of the tables often comes from institutions that dislike their position in them. Few of those who compile the tables, they add, claim that their figures capture everything that matters about a university.

What difference the tables actually make to students is less clear than is often assumed. Surveys of international applicants suggest that most consult rankings at some stage, but few say that they are decisive. Cost, the availability of a particular course, the location of family and friends and the chance of a scholarship generally matter more. Their influence appears strongest among postgraduates, who are choosing between offers that are otherwise similar. It is also strong among families with no direct experience of universities, for whom a published position is a rare signal in an unfamiliar market.

Governments have been more responsive. Several countries require candidates for state scholarships to study at institutions inside a certain band of the tables. Others have set their universities explicit targets for entry into the top hundred, sometimes concentrating extra funding on a small number of institutions in the expectation that this will create a world-class university. Researchers who study higher education warn that such policies narrow a national system to a handful of institutions, leaving the teaching-intensive universities that educate most students without the resources or the prestige to improve.

My own view is that the balance of harm is clear, though not for the reason usually given. The problem is not that the numbers are wrong; most compilers are careful, and the indicators measure what they claim to measure. It is that a narrow set of measurable outputs has become a proxy for the value of a university as a whole. Rankings answer the question of which institution produces the most research of a kind that is easily counted. They do not answer the questions that most people actually ask. A better approach would publish several separate profiles, of teaching, of research and of regional contribution, and refuse to combine them into a single order. Until that happens, rankings will continue to do more harm than good.