IELTS Academic Reading Practice Test 471

On 19 July 1545 a French invasion fleet of about two hundred ships entered the Solent, the narrow channel that separates the Isle of Wight from the south coast of England. Henry VIII watched from the battlements of Southsea Castle as the English fleet moved out to meet the threat. Among the largest of the king's ships was the Mary Rose, a carvel-built warship of some 500 tons. Shortly after she fired her first broadside she heeled over, water poured through her open gunports, and she went down in full view of the shore. Fewer than forty of the four hundred or so men on board survived.

The ship had been built at Portsmouth in 1509–11, early in Henry's reign, and refitted in 1536, when she was given an extra tier of guns. Like other warships of the period she was carvel-built: her hull planks were laid flush, edge to edge, rather than overlapping in the older clinker fashion, which produced a smooth surface strong enough to carry heavy ordnance. Her armament was her defining feature. Instead of firing only from the deck, she carried heavy iron guns in a row along her lower hull, each aimed through a hinged port cut close to the waterline. The arrangement gave her a devastating broadside, but it also meant that a few degrees of heel could bring the lowest ports under the sea.

Why she capsized has been argued over for centuries. The most common contemporary explanation was indiscipline: the crew, it was said, failed to close the lower ports after firing, and a sudden gust then pushed the hull over. Naval architects who have studied the wreck have added a structural factor. The lowest row of ports sat barely a metre above the water, and at that height any appreciable list, whether from wind, from the recoil of the guns or from the movement of several hundred men to one side, would have taken them below the surface. The ship may also have been overloaded with men and equipment.

For more than four centuries the wreck lay in the mud of the Solent, its timbers protected by sediment. Sealed in silt and starved of oxygen, and therefore out of reach of the shipworm that destroys exposed wood in the sea, the hull survived where most wrecks disintegrate. Everything above the level of the silt — the upper decks, the masts and the rigging — had long since been destroyed. In 1971, after years of searching with sonar and by eye, a team led by the amateur historian Alexander McKee located the buried hull. Around it lay a layer of objects that had slipped down with the ship and settled with her.

Excavation was a slow and difficult business, carried out by divers working in poor visibility and strong tides. They worked in short shifts, lifting spoil by hand, and every object was recorded in position before it was removed. The Mary Rose Trust, formed in 1979, raised the money for a full recovery. On 11 October 1982 the remaining hull, supported within a steel frame, was lifted by crane onto a barge and taken to a dry dock in Portsmouth while a television audience watched. It was the largest underwater excavation of its kind attempted at that time.

Conservation then became the central problem. Waterlogged oak that is allowed to dry out collapses, because the water that has filled the cells of the wood for centuries evaporates and the cell walls shrink and crush one another. From 1994 the hull was sprayed continuously with a solution of polyethylene glycol, a waxy polymer whose molecules penetrate the timber and support its structure as the water is gradually removed. The treatment took many years, and only in the 2010s did conservators begin the slow, carefully monitored process of air-drying, watched by sensors embedded in the wood.

Some 19,000 objects have been recovered from the site, an exceptionally rich collection because the ship went down suddenly, with everything on board. Among them are longbows by the hundred — the largest group of medieval and Tudor bows in existence — a barber-surgeon's chest still holding its jars and instruments, wooden plates and combs, dice, leather shoes and the skeleton of a small dog. The skeletons of about 179 individuals were also recovered, and they have been examined for evidence of diet, disease and injury.

Such finds matter because the everyday possessions of ordinary people in the sixteenth century survive hardly at all. What remains from the period is mostly the contents of churches, the houses of the wealthy and the written records of government. The Mary Rose offers something different: a single moment of ordinary working life, preserved in mud, with the objects still lying where the men who used them dropped them.

In 2013 the Mary Rose Museum opened in Portsmouth Historic Dockyard, designed so that the hull and the objects found with it can be seen together: the ship stands behind glass, with visitors on galleries overlooking it from three sides. Conservation continues, the timbers are still monitored and adjusted, and the study of what was recovered is far from complete.

Over the past two and a half million years the Earth has passed repeatedly between glacial periods, when vast ice sheets covered much of northern Europe and North America, and shorter warm intervals such as the one in which we now live. In the 1960s and 1970s researchers established the basic pattern from deep-sea sediments. Oxygen isotopes in the shells of tiny marine organisms record how much water was locked up in ice at any given time, and the record they produced showed a rhythm of roughly 40,000 years. About a million years ago, however, the cycles became longer, close to 100,000 years, and far more extreme. This shift is known as the Mid-Pleistocene Transition, and its cause is still argued about.

Naturalists had suspected long before that ice had once covered Europe. Erratic boulders, resting far from any rock of the same type, and spreads of gravel and clay in Alpine valleys could be explained if glaciers had once been far larger. In 1837 the Swiss-American naturalist Louis Agassiz went further, proposing to a scientific meeting that a great ice age had affected much of the northern hemisphere and not merely mountain regions. The idea was resisted at first, but by the end of the century geologists had mapped the deposits left by ice sheets across Europe and North America, and the existence of past glaciations was accepted.

What could cause such changes? In the 1860s the Scottish scientist James Croll suggested that variations in the Earth's orbit might alter the amount of sunlight reaching high latitudes. In the 1920s and 1930s the Serbian mathematician Milutin Milanković worked out the idea in detail. Three features of the planet's orbit vary: its shape, which shifts from more circular to more elliptical over about 100,000 years; the angle of its axis, which swings between roughly 22 and 24.5 degrees over about 41,000 years; and the direction in which the axis points, which traces a slow cone over some 23,000 years. Each changes the distribution of sunlight by season and latitude, even though the total amount reaching the Earth barely alters.

Milanković's theory was not widely accepted in his lifetime, because the geological evidence was too imprecise to test it. That changed with the deep-sea cores. In 1976 three researchers published an analysis of two sediment cores from the southern Indian Ocean, in which the oxygen-isotope record could be matched, cycle by cycle, against the calculated orbital variations. The match was close enough to persuade most of the scientific community that orbital cycles set the timing of the ice ages. The paper was titled 'Variations in the Earth's Orbit: Pacemaker of the Ice Ages', and the word pacemaker has been used ever since.

Orbital change alone, however, cannot explain the size of the swings. The direct effect of the cycles on the energy the Earth receives is small, and something must amplify it. Several feedbacks do so. Ice and snow reflect far more sunlight than land or sea, so an ice sheet that grows a little cools the region around it, which allows more ice to form. Carbon dioxide works in the same direction: air trapped in Antarctic ice cores shows that its concentration fell to about 180 parts per million during glacial periods and rose to about 280 in the warm intervals between them. Warming oceans and changing marine life appear to have released and absorbed the gas in step with the ice, amplifying the orbital signal.

The end of a glacial period is more abrupt than its beginning. The trigger is usually a rise in summer sunlight at high northern latitudes, produced by the orbital cycle described above. Ice sheets take tens of thousands of years to build, but they can disappear in a fraction of that time, because once melting starts, the shrinking white surface absorbs more heat and the process accelerates. Meltwater flooding into the North Atlantic can weaken the circulation that carries warm water northwards, which in turn shifts rainfall patterns across the tropics. Sea level rises by more than a hundred metres between a glacial maximum and an interglacial, drowning coastlines that had been dry land for millennia.

Over millions of years a quite different process regulates the planet's temperature. Silicate rocks exposed to the atmosphere are slowly broken down by chemical weathering, a reaction that consumes carbon dioxide and locks it away in carbonate minerals. Because the rate of the reaction rises with temperature, it acts as a thermostat: warmer conditions speed the removal of the gas and cool the planet. Mountain building exposes fresh rock to the air, and the uplift of the Himalayas and the Tibetan plateau has been proposed as one reason why the Earth cooled gradually through the last few tens of millions of years. The movement of continents can also alter the routes taken by ocean currents, which may help to determine where ice sheets are able to grow.

Many questions remain. The most stubborn is why the 100,000-year rhythm dominates the later record when changes in the shape of the Earth's orbit alter the total amount of sunlight so slightly; computer models of ice sheets still struggle to reproduce it. The future is a puzzle of a different kind. Calculations suggest that, without human interference, the present warm interval would last tens of thousands of years before the next glaciation began. Whether the carbon dioxide released by burning fossil fuels has already postponed that event, and by how long, is a question that no one can yet answer with confidence.

The floor of the deep ocean is scattered with small dark lumps known as polymetallic nodules, which form over millions of years as metals dissolved in seawater precipitate around a fragment of shell, a tooth or an older nodule. The nodules are rich in manganese, nickel, copper and cobalt, and they lie in enormous numbers on the abyssal plains, above all in the Clarion-Clipperton Zone, a stretch of the central Pacific between Hawaii and Mexico. They were first dredged up in the nineteenth century, but their extent became clear only in the 1960s and after. Metal-rich crusts on the slopes of underwater mountains, and the deposits that form around hydrothermal vents, are also candidates for extraction. These metals are essential to the batteries, magnets and cables on which the shift away from fossil fuels is widely expected to depend.

The United Nations Convention on the Law of the Sea, agreed in 1982, declares the deep seabed beyond national jurisdiction to be the common heritage of mankind, and it created the International Seabed Authority, based in Kingston, Jamaica, to administer the area. The Authority has granted many contracts allowing states and companies to explore particular areas, but it has not adopted the regulations that would permit commercial exploitation. In 2021 the Pacific island state of Nauru, which sponsors a mining company, gave notice that it intended to apply for one. Under the rules this started a two-year deadline for the Authority to finish its code; the deadline passed in 2023 with no code agreed.

Supporters of mining argue that demand for these metals will rise steeply as electric vehicles and renewable energy replace oil, coal and gas, and that the richest deposits on land are becoming harder to work and are concentrated in a few countries where supply may be disrupted. Critics reply that the commercial case has never been demonstrated: no deep-sea mine operates anywhere in the world, and the cost of lifting nodules from four kilometres of water and processing them is unknown. They add that recycling, better battery design and the substitution of other materials could reduce demand substantially. Prices of nickel and cobalt have also swung widely over the past decade, which makes long-term investment risky. In my view the economic case rests on projections rather than on evidence.

The ecological objections are harder to dismiss. The abyssal plain is one of the least studied environments on Earth, and much of what lives there is unknown: a high proportion of the animals collected by biologists turn out to be new to science. The nodules themselves are a habitat, since they provide almost the only hard surface on a plain of fine sediment, and slow-growing animals such as sponges and corals settle on them. Nodules accumulate at a rate of a few millimetres every million years, so they cannot be replaced within any span of time that matters to people. Disturbance is long-lasting as well: when researchers returned to a track cut through the sediment by a test in 1978, they found it still clearly visible, and the community of small animals living in the mud had not recovered.

Faced with such uncertainty, several governments, including France and Germany, have argued that no commercial mining should be approved until the risks are better understood and the rules are in place. Many marine scientists have signed statements calling for a pause, and several manufacturers, among them car and electronics companies, have promised not to buy metals taken from the deep sea. Others are impatient. Small island states that sponsor exploration contracts hope that royalties will fund development, and they point out that a delay is of little comfort to countries with no other source of income. Critics of a pause add that it would not stop mining everywhere but would merely push it into the national waters of states that choose to allow it, where international standards do not apply.

My own position is that commercial mining should not begin yet. The damage that would be done is likely to be irreversible within any human timeframe, while the benefits are speculative and might be met by other means; where the harm is permanent and the gain uncertain, delay is not obstruction but ordinary caution. I do not rule out that extraction may one day be justified, and continued exploration, properly funded and openly published, is the only way to find out. What I would defend is a pause of a decade or so, tied to independent baseline surveys, to monitoring of each site for years before any large-scale operation begins, and to a rule that no contract is granted while the Authority's code remains incomplete.