IELTS Academic Reading Practice Test 475

In the summer of 1903 a farmer digging into a large mound on the Oseberg farm, near the town of Tønsberg in southern Norway, struck a piece of carved timber. Beneath the mound lay a Viking ship, buried a thousand years earlier with two women and a remarkable collection of objects. Blue clay in the subsoil had sealed the grave from the air, so the oak of the hull and much of what it contained had survived. Nothing on this scale had been found before, and the excavation that followed changed scholars' picture of the Viking Age. For archaeologists of the period it was the find of a lifetime.

The excavation was supervised by the archaeologist Gabriel Gustafson, assisted by his younger colleague Haakon Shetelig, and the digging occupied a single summer, in 1904. Lifting the ship was slow and cautious. The waterlogged oak was soft enough to crush between finger and thumb, and it would have crumbled if allowed to dry out. Each timber was therefore recorded, numbered, wrapped in wet cloth and taken to Oslo, where the vessel was later rebuilt over an internal frame. What visitors see today is in that sense a reconstruction: most of the wood is original, but its shape is held by modern supports.

The ship is a slender vessel about twenty-one metres long and five metres wide. It is built in the clinker tradition, with overlapping planks of oak riveted together and caulked so that the hull would flex in a seaway. Fifteen oar holes on each side show that it was rowed by around thirty men, and a heavy steering oar is mounted on the right-hand, or starboard, side. The remains of a mast support prove that it also carried a sail, though its shallow draught and low sides suggest a vessel meant mainly for coastal waters rather than the open ocean. Both ends of the hull rise into elegant spiral posts, and the upper strakes are carved with interlocking animals.

Dendrochronology, the dating of timber by the pattern of its tree rings, indicates that the oak was felled around the year 820. The burial chamber was built of timbers cut a little later, and the grave appears to have been closed in 834. The ship may therefore have been in use for some years before it was hauled ashore to serve as a coffin — evidence that a vessel of this kind was valuable enough to justify an elaborate ceremony.

Of the two occupants, the elder was a woman of about eighty and the younger perhaps fifty. Both wore garments of fine wool, some of them woven with silk, and both lay in a chamber furnished as a bedchamber. Who they were has never been established. It has been suggested that the elder woman was Queen Åsa, mother of a ninth-century Norwegian ruler, but the guess rests on little more than the richness of the grave, and no inscription names her. Whether the younger woman was a relative, a servant or someone who died to accompany her mistress is equally unclear.

Apart from the ship, the grave contained a four-wheeled cart, four sledges and three beds, along with chests, cooking equipment and looms. There were five carved posts topped with animal heads, perhaps carried in processions, and a wooden bucket whose bronze mounts include a small seated figure with crossed legs, generally identified as a version of a Buddhist motif that had travelled north along trade routes. Textiles survived in extraordinary quantity, among them fragments of a tapestry showing figures, wagons and trees that may record a ritual. The grave also held the bones of horses, dogs, cattle and at least one peacock.

The mound had been robbed in the distant past. Intruders dug a shaft down into the chamber, removed the metal objects and anything else of value, and disturbed the bodies. Their visit has proved useful in one respect: they abandoned several wooden shovels in the trench they had dug, and these, preserved in the same wet clay as everything else, are among the few tools of their kind to survive from the Viking Age.

Because the hull had lost much of its strength, the ship was displayed for decades on a framework of metal and wood in a museum on the Bygdøy peninsula in Oslo. In recent years concern about its condition grew, for the timbers were slowly deforming under their own weight and the supports themselves were thought to be causing damage. A new museum building, designed to hold the vessel under gentler conditions, is being constructed on the same site. Conservation of the Oseberg wood, in short, is a process that has never quite ended.

The finds also gave art historians a vocabulary. The dense animal ornament that covers the ship and many of the objects buried with it is now known as the Oseberg style, an idiom that spread across Scandinavia. More broadly, the grave revealed a world that traded with Asia, honoured wealthy women with spectacular burials and employed craftsmen of extraordinary skill. A single waterlogged mound, it turned out, could say more about a society than a hundred scattered finds.

Wood is one of the most durable materials that plants make, and its durability is chemical rather than physical. Roughly half of dry wood is cellulose, long chains of sugar molecules bundled together into fibres. Perhaps a quarter is hemicellulose, a family of shorter, branched sugars. The remainder is lignin, a complex aromatic polymer that encases the fibres and makes timber rigid and waterproof. Cellulose and hemicellulose can be digested by a great many organisms, from bacteria to beetles, but lignin is a different matter. Its random, tightly cross-linked structure resists the enzymes that most living things possess, and only a few kinds of microbe can dismantle it. Of those, by far the most important are the fungi that cause wood to rot. Their success is a matter of chemistry rather than strength, and it depends on water: a fungus can work only in timber that is damp.

A wood-decaying fungus usually begins as a spore that lands on a wound, a broken branch or a sawn end. If the wood holds enough water — commonly reckoned at above about twenty per cent by weight — the spore germinates and puts out a thread called a hypha. Hyphae extend only at their tips, growing by a few micrometres an hour, and they branch repeatedly to form a network known as a mycelium that spreads through the timber in search of food. A hypha cannot swallow a piece of wood, so the fungus digests its meal outside its own body, releasing enzymes and other reactive substances into the wood and absorbing the soluble products. To pass from one cell to the next, hyphae slip through the pits, the small openings in the cell walls; once inside, they can bore through the wall itself. Water is essential throughout, because without a continuous film of it enzymes cannot travel and the process stalls.

The white rots are the most thorough of the decayers. They attack lignin as well as cellulose, using an armoury of oxidative enzymes that require oxygen and, in some species, generate hydrogen peroxide as a weapon. What remains is a pale, fibrous, stringy residue, which gives the group its name. Because they can destroy lignin, white rot fungi are the only organisms capable of returning all of the carbon in a fallen tree to the atmosphere within a reasonable period, and in forests they are the principal agents of that process. Some species are highly selective, stripping out lignin while leaving much of the cellulose intact, and this preference has attracted the interest of industries that wish to separate the two components cleanly.

Brown rot fungi take a different route. They remove cellulose and hemicellulose but leave most of the lignin, altering it chemically so that the residue cracks into cubical chunks and darkens; the crumbly brown wood that breaks apart underfoot is the result. How they begin the attack is a puzzle. The enzymes that digest cellulose are far too large to pass through the narrow pits between wood cells, so brown rots must open the assault with something much smaller. The leading explanation involves Fenton chemistry, in which the fungus produces hydrogen peroxide and uses iron ions to turn it into highly reactive radicals that attack the cellulose directly. Fungi are also known to secrete oxalic acid, which helps to create the necessary conditions and loosens the bonds between lignin and cellulose. The precise sequence is still disputed, however, and different species may not work in the same way.

Not all decay happens in forests. Soft rot fungi, which tolerate conditions of extreme wetness or dryness that defeat other species, tunnel along the inside of cell walls and are common in waterlogged timber and in wood exposed to the weather. In buildings the most feared species is the dry rot fungus, unusual in its ability to conduct water along thick strands of mycelium from damp masonry to dry timber, so that it spreads far from the original leak. It also produces thick, root-like cords that can cross a brick wall in search of food. A fruiting body — a flat, rust-coloured bracket on a skirting board or a joist — usually appears only when the damage is extensive. Repairs to timber damaged by fungi cost property owners large sums every year.

In the wider world the importance of wood decay is hard to overstate. In a temperate forest most of the carbon that enters the soil has passed through a fungus, and without decay dead wood and leaf litter would pile up and the nutrients locked inside them would never be released. Some decayers are also formidable in size: a single individual of the honey fungus in a forest in Oregon has been estimated to extend over nearly ten square kilometres, which would make it one of the largest organisms known. There is a commercial interest too. If industry could imitate brown rot, breaking wood down with small, cheap molecules rather than costly enzymes, the manufacture of fuel from plant waste might become much easier. How close that ambition is to being realised is another question; the chemistry of decay is still being worked out.

Few proposals in education divide opinion as sharply as the suggestion that teachers' pay should depend on how well their pupils perform in tests. In its simplest form the argument is that teaching is one of the last professions in which a person's income rises automatically with the years and has no connection with results, and that this arrangement is both unfair and inefficient. I want to argue that the case for paying individuals according to test scores is weaker than it appears, though not for the reasons its opponents usually give.

Economists who favour performance pay start from a general principle: in most occupations earnings reflect what a person produces, and teaching is one of the few professions in which pay rises automatically with length of service and is unrelated to results. On this view a uniform salary scale makes it hard to reward excellent teachers, gives able graduates little reason to choose teaching over better-paid careers, and allows the colleague who works hard and the one who does the minimum to be paid identically. The complaint is not that teachers are lazy. It is that the system sends no signal at all about who is doing the job well.

Teachers' organisations have resisted such schemes almost everywhere they have been tried, and their objections are not merely self-interested. They point out that a pupil's results reflect the home they come from as much as the effort of any single teacher, and that a scheme which sets colleagues in competition is damaging in schools where cooperation is essential. Leaders of those organisations have also warned of dishonesty. In one American city, an investigation in 2011 found that staff had altered pupils' answer sheets, and teachers elsewhere have described pressure to concentrate on the pupils close to a pass mark, neglecting both the weakest and the most able.

The technical objection is more serious still. To link pay to results, one must isolate the contribution of an individual teacher, and that is extraordinarily difficult. Value-added models, which compare the progress of a class with that of similar pupils elsewhere, are the most sophisticated instrument available, yet the statisticians who construct them are cautious about how their figures should be used. Their estimates are unstable. A teacher's score can move substantially from one year to the next, or when the class changes, because of random variation and the composition of the group.

Evidence from schemes that have actually operated is mixed. Evaluations of bonus programmes in lower-income countries have generally found modest gains in test scores while the money was on offer, and thinner evidence that anything in the classroom had changed. In one widely cited scheme the improvement was not sustained after the payments stopped, which suggests that the incentive altered behaviour rather than teaching. Richer countries offer a muddier picture, partly because their schemes differ so much in size, in whether bonuses go to individuals or to whole schools, and in how far teachers helped to design them.

Where bonuses have been paid to a whole school rather than to individuals, the effects appear somewhat more consistent, and this is not surprising. Schools are collective enterprises: a pupil's progress in one subject depends on what was taught in previous years, on the work of several colleagues and on the stability of the staff. Rewarding a staff collectively encourages the cooperation that individual competition erodes. Some campaigners therefore argue that any extra money would be better spent on schools serving disadvantaged communities and on subjects such as mathematics and physics, where vacancies are hard to fill.

None of this means that current pay arrangements are satisfactory. A scale that rewards time served and ignores everything else is hard to defend, and the difficulty of recruiting physics and computing specialists is real. But the alternative on offer — individual bonuses calculated from pupils' test scores — solves one problem by creating several worse ones. It narrows what is taught, since subjects that are not tested come to seem less important. It penalises teachers who agree to take on the most difficult classes. Above all, it rests on measurements that cannot bear the weight placed upon them.

Some countries have gone further than others. In England, a reform introduced in 2013 gave schools much greater freedom to decide how teachers' pay should progress, and in Sweden individual pay setting has been common for decades. Neither case offers a clean natural experiment, because pay arrangements changed alongside many other things, but neither has produced the transformation that advocates predicted or the collapse that critics feared.

My own view is that performance should indeed influence pay, but that the performance that matters cannot be reduced to a test score. Teachers who move to a school in a disadvantaged area, who take on a subject for which there are no applicants, or who mentor three new colleagues are doing work that a sensible salary system ought to recognise. Such judgements are inevitably local and human; they require a head teacher to observe, discuss and occasionally defend a decision to the staffroom. That is more troublesome than a formula, but it is also more honest, and it is less likely to reward the wrong things.