IELTS Academic Reading Practice Test 79

Until the nineteenth century, timekeeping was governed by the sun. Each town kept its own local time, setting its public clocks so that noon occurred when the sun reached its highest point in the sky. Because the sun appears to move from east to west, towns only a short distance apart experienced noon at slightly different moments, and their clocks therefore differed by a few minutes. As long as travel was slow and communication limited, these small discrepancies mattered little, and nobody expected a clock in one place to agree exactly with a clock in another.

The coming of the railways made such variety untenable. A railway company running trains across a country needed a single timetable, but if stations along the line each kept their own time, the timetable became confusing and accidents could occur. In Britain, the Great Western Railway took the lead in 1840 by ordering that London time be used at all its stations. Other companies followed, and by the middle of the century railway time, based on the Royal Observatory at Greenwich, had become the practical standard for rail travel throughout the country.

Greenwich time was not suddenly invented for the railways. The Royal Observatory, founded in 1675, had long supplied astronomical data for navigation, and from 1833 a bright time ball was dropped from its roof every day at one o'clock so that ships on the Thames could check their chronometers. In the 1850s, electric telegraph lines began to carry Greenwich time signals across the country, allowing distant towns to set their public clocks accurately. In this way, a single authority gradually became the source of standard time for Britain.

North America faced the same difficulty on a larger scale. In the United States and Canada, hundreds of different local times were in use, and each railway tended to adopt the time of its own principal city, so that stations serving several lines displayed several different clocks. The problem was solved by the railways themselves rather than by governments. On 18 November 1883, the American and Canadian railroads introduced four standard time zones across the continent – Eastern, Central, Mountain and Pacific – each one hour apart. The new arrangement was quickly accepted by most cities, although it did not become federal law in the United States until 1918.

The choice of Greenwich as the world's reference point owed much to the sea. British navigators had begun using the Greenwich meridian on their charts in the eighteenth century, and by the late nineteenth century most nautical charts and maps produced in many countries were based upon it. A standard meridian for longitude was therefore already a practical reality long before any formal international agreement.

Standard time within one country, however, was not enough for an age of global telegraphic communication and long-distance navigation. It was necessary to agree on a common starting point from which to measure longitude and time around the world. In October 1884, delegates from twenty-five nations met in Washington for the International Meridian Conference. They adopted the meridian passing through the Royal Observatory at Greenwich as the prime meridian for the whole world, and recommended that the universal day should be a mean solar day beginning at midnight at Greenwich. The conference did not impose time zones, but its decisions laid the foundation for the system used today.

The time-zone system based on Greenwich divides the globe into twenty-four zones, each ideally fifteen degrees of longitude wide, with local time one hour ahead of or behind its neighbours. In practice, governments have adjusted the boundaries to follow administrative borders or economic links, and many places use zones that differ from Greenwich by half an hour or even a quarter. China, for example, officially uses one time zone across a country that spans five geographical zones, while island states in the Pacific have at times shifted the international date line to suit their trading partners.

The original standard time was based on the rotation of the Earth, but astronomers discovered that this rotation is not perfectly steady. In the twentieth century, therefore, timekeeping moved from astronomical observation to atomic physics. Atomic clocks, which measure the vibration of atoms, are so stable that they lose or gain less than a second over millions of years. Since 1972, the world has used Coordinated Universal Time, or UTC, which is based on atomic time but is occasionally adjusted by the addition of a leap second to keep it in step with the Earth's rotation.

The adoption of standard time was gradual and sometimes resisted. Some communities resented having their clocks changed by distant authorities, and for years public clocks showed both local and railway time. Yet the benefits of agreement were overwhelming. In an interconnected world, standard time has become one of those invisible systems that make modern life possible, from airline schedules and financial markets to the simple act of agreeing to meet at a particular hour.

The history of standard time shows how a practical problem can lead to worldwide cooperation. What began as a way to keep the trains running smoothly ended up defining the daily rhythm of almost every human activity, and it now seems natural that the whole planet should share a single, agreed system of hours.

A meteoroid is a small piece of rock or metal travelling through space, ranging in size from a grain of dust to a boulder several metres across. When such an object enters the Earth's atmosphere, friction with the air heats it until it glows, producing the streak of light known as a meteor, or shooting star. Most meteoroids are destroyed completely during this fiery descent, but a few survive the passage and reach the ground, where they are called meteorites. It is only in this final stage that these objects can be picked up and studied, and each one is a direct sample of material from beyond our planet.

Meteorites are traditionally divided into three broad groups. The most common are stones, which make up the great majority of falls and are composed mainly of silicate minerals, although many also contain small grains of metal. Iron meteorites consist almost entirely of metallic iron and nickel, and stony-iron meteorites contain a mixture of both. Although iron meteorites are far less common among objects seen to fall, they are heavily over-represented in collections because their dense, rusting remains are much easier to recognise on the ground than ordinary stones. The classification is not merely descriptive, as the three groups appear to come from different regions of their parent bodies.

Most meteorites come from the asteroid belt between Mars and Jupiter, where countless rocky bodies have been colliding and breaking apart for billions of years. Collisions in this region send fragments into orbits that can cross the Earth's path. A small but scientifically precious subset can be linked to the Moon and Mars. These are identified by comparing their minerals and trapped gases with lunar samples returned by space missions and with measurements made on Mars by landers, and they offer a rare opportunity to study another planetary body without leaving Earth. Some Martian meteorites contain tiny bubbles of gas whose composition matches the Martian atmosphere measured by landers.

Meteorites are described either as falls or finds. A fall is a meteorite that is witnessed arriving and collected soon afterwards, while a find is a meteorite discovered by chance long after it has landed. Witnessed falls are comparatively rare, because most of the Earth is ocean or thinly populated, and a meteorite that lands unnoticed may be buried, weathered or covered by vegetation. Consequently, the majority of specimens in museums are finds, and their study depends on recognising them among ordinary terrestrial rocks. Hot deserts have also become productive because dark stones are visible on pale sand.

For centuries, reports of stones falling from the sky were treated with suspicion by educated Europeans. It was not until 1803, when the French scientist Jean-Baptiste Biot investigated a shower of stones at L'Aigle in Normandy and found thousands of fragments scattered over the countryside, that the reality of meteorite falls became widely accepted. Since then, meteorites have moved from curiosities to objects of serious scientific study, and every witnessed fall is treated as an opportunity to test ideas about the formation of the planets.

Antarctica has proved to be the most productive hunting ground on the planet. Dark meteorites stand out clearly against the bright blue ice, and the cold, dry conditions slow the weathering that destroys such objects elsewhere. In addition, glacial ice can carry meteorites downhill over thousands of years and concentrate them in areas where old ice is exposed at the surface. Teams of scientists have recovered tens of thousands of specimens from these so-called stranding surfaces, transforming the supply of extraterrestrial material available for research. Because the ice preserves even fragile meteorites, many important specimens, including the famous Martian meteorite ALH84001, have been found there.

Because many meteorites have remained almost unchanged since the solar system formed about 4.6 billion years ago, they preserve a record of its earliest history. Chondrites, the most primitive stones, contain tiny spherical droplets called chondrules that solidified very early from molten material, and some also contain calcium-aluminium-rich inclusions, which may be among the first solids to form. Carbonaceous chondrites additionally contain water and complex organic molecules, including amino acids. The Murchison meteorite, which fell over Australia in 1969, was analysed soon after landing and found to contain more than seventy amino acids, showing that the building blocks of life can form away from the Earth.

Large meteorite impacts have also shaped the Earth itself. In Arizona, Meteor Crater is a bowl about 1.2 kilometres across that was excavated around 50,000 years ago by an iron meteorite perhaps 50 metres in diameter. Much larger impacts have been linked to global effects, and it is now widely accepted that an enormous collision at the end of the Cretaceous period, 66 million years ago, contributed to the extinction of the dinosaurs and many other species. Such collisions are rare on human timescales, but they demonstrate the continuing influence of extraterrestrial objects.

In recent years, scientists have tried to increase the number of meteorites that are observed as they fall. Networks of cameras monitor the night sky, and radar can sometimes detect rocks descending through the atmosphere, allowing searchers to calculate a likely landing area. One celebrated success came in 2021, when the Winchcombe meteorite was recovered in England within days of being seen on camera, preserving fragile minerals that would have been destroyed by rain and weathering. Such rapid recovery is important because it connects a meteorite's chemical make-up with its original orbit, linking laboratory analysis to a particular region of the solar system.

Every historic building is a document, and like any document it can be read in different ways. When a building is damaged or decayed, the question of what should be done with it becomes urgent. Some argue that it should be returned to the condition intended by its original builders; others insist that any change to the surviving fabric destroys evidence that can never be recovered. My own view is that the first duty of those responsible for old buildings is to preserve what has actually survived, and that restoration should be no more than a cautious means to that end.

The debate has deep roots. In the nineteenth century, the French architect Eugène Viollet-le-Duc restored medieval buildings such as the fortified city of Carcassonne to an idealised state that they may never have possessed. His English contemporary John Ruskin took the opposite position, arguing that restoration is the worst form of destruction because it replaces the original work of the craftsman with a modern imitation. Ruskin's words are often quoted by conservationists, and I believe that, on this fundamental point, he was right. Viollet-le-Duc's approach was enormously influential, and many of his restorations are now admired as works of architecture in their own right.

The reason lies in the information carried by old materials. A wall built in the twelfth century is not simply a structure; it is evidence of the tools, techniques and economic conditions of its time. Every worn step and repaired joint records a history of use that cannot be inferred from drawings. When such material is removed and replaced with new stone shaped to match, the building may look older or more complete, but the knowledge stored in it has been destroyed. The loss is irreversible, even if the result is visually convincing.

This does not mean that historic buildings must be frozen and left to decay. Buildings survive by being used, and use may require alterations. The key is that modern additions should be clearly distinguishable from old fabric and, where possible, reversible. A steel and glass extension to a medieval hall may be criticised by some, but it is often more honest than a fake stone wing designed to deceive. The accepted principle in contemporary conservation, set out in international charters, is that new work should be identifiable on close inspection.

The most difficult cases are buildings that have been almost completely destroyed. After the Second World War, the historic centres of Warsaw and other European cities were rebuilt from ruins, often using old photographs and paintings as evidence. These reconstructions have become deeply valued by residents and visitors, and to call them fakes seems harsh. Nevertheless, I would argue that such rebuilding should be regarded as exceptional. It is justified when a community needs to recover its identity after disaster, but not as a routine way of turning a ruin into a tourist attraction.

Economic pressures present a constant temptation to over-restore. A complete, brightly painted interior may attract more visitors than a fragmentary wall, and heritage bodies sometimes face demands to make monuments more legible by rebuilding missing parts. Yet legibility should not require invention. Much can be done with careful presentation, lighting and explanatory panels, which help visitors understand a building without pretending that the gaps are not there. In my view, a ruin honestly presented is often more instructive than a reconstruction that fills every gap. The best interpretation is usually the one that respects the evidence rather than the imagination.

There is also the question of technique. Traditional materials such as lime mortar and hand-made brick often behave differently from modern cement and machine-made products, and their replacement can damage the surrounding masonry. Skilled conservation therefore depends on craftspeople who understand the original methods, and on owners who are willing to pay for patience rather than speed. The loss of these practical skills is as serious as the loss of the buildings themselves, because once a craft tradition has disappeared, it is extremely difficult to revive.

When a historic building has lost its roof, there is a temptation to rebuild it in a conjectural form. In some cases, archaeological evidence can provide a basis for this, but the line between evidence and imagination is easily crossed. If a reconstruction is presented as a hypothesis rather than as a faithful copy, it can be valuable. The problem arises when visitors are led to believe that what they see is original. Clear labelling and a visible difference between old and new work are essential if reconstruction is to remain intellectually honest.

However, I am not opposed to all change. A building that becomes a museum piece may lose the very life that made it significant. The challenge is to manage change without destroying the qualities that make a place valuable. This requires clear principles, independent advice and a willingness to say no to proposals that would harm the special character of a building, however profitable they may be. It also requires humility: we should assume that future generations will know more than we do, and that what we leave untouched will be studied with techniques we cannot yet imagine.