Reading 2026-01 Test 4

A The oceans of Earth cover more than 70 percent of the planet’s surface, yet, until quite recently, we knew less about their depths than we did about the surface of the Moon. Distant as it is, the Moon has been far more accessible to study because astronomers long have been able to look at its surface, first with the naked eye and then with the telescope—both instruments that focus light. And, with telescopes tuned to different wavelengths of light, modern astronomers can not only analyze Earth’s atmosphere, but also determine the temperature and composition of the Sun or other stars many hundreds of light-years away. Until the twentieth century, however, no analogous instruments were available for the study of Earth’s oceans: Light, which can travel trillions of miles through the vast vacuum of space, cannot penetrate very far in seawater. B Curious investigators long have been fascinated by sound and the way it travels in water. As early as 1490, Leonardo da Vinci observed: “If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you.” In 1687, the first mathematical theory of sound propagation was published by Sir Isaac Newton in his Philosophiae Naturalis Principia Mathematica. Investigators were measuring the speed of sound in air beginning in the mid seventeenth century, but it was not until 1826 that Daniel Colladon, a Swiss physicist, and Charles Sturm, a French mathematician, accurately measured its speed in water. Using a long tube to listen underwater (as da Vinci had suggested), they recorded how fast the sound of a submerged bell traveled across Lake Geneva. Their result—1,435 meters (1,569 yards) per second in water of 1.8 degrees Celsius (35 degrees Fahrenheit)—was only 3 meters per second off from the speed accepted today. What these investigators demonstrated was that water—whether fresh or salt—is an excellent medium for sound, transmitting it almost five times faster than its speed in air. C In 1877 and 1878, the British scientist John William Strutt, third Baron Rayleigh, published his two-volume seminal work, The Theory of Sound, often regarded as marking the beginning of the modern study of acoustics. The recipient of the Nobel Prize for Physics in 1904 for his successful isolation of the element argon, Lord Rayleigh made key discoveries in the fields of acoustics and optics that are critical to the theory of wave propagation in fluids. Among other things, Lord Rayleigh was the first to describe a sound wave as a mathematical equation (the basis of all theoretical work on acoustics) and the first to describe how small particles in the atmosphere scatter certain wavelengths of sunlight, a principle that also applies to the behavior of sound waves in water. D A number of factors influence how far sound travels underwater and how long it lasts. For one, particles in seawater can reflect, scatter, and absorb certain frequencies of sound—just as certain wavelengths of light may be reflected, scattered, and absorbed by specific types of particles in the atmosphere. Seawater absorbs 30 times the amount of sound absorbed by distilled water, with specific chemicals (such as magnesium sulfate and boric acid) damping out certain frequencies of sound. Researchers also learned that low frequency sounds, whose long wavelengths generally pass over tiny particles, tend to travel farther without loss through absorption or scattering. Further work on the effects of salinity, temperature, and pressure on the speed of sound has yielded fascinating insights into the structure of the ocean. Speaking generally, the ocean is divided into horizontal layers in which sound speed is influenced more greatly by temperature in the upper regions and by pressure in the lower depths. At the surface is a sun-warmed upper layer, the actual temperature and thickness of which varies with the season. At mid-latitudes, this layer tends to be isothermal, that is, the temperature tends to be uniform throughout the layer because the water is well mixed by the action of waves, winds, and convection currents; a sound signal moving down through this layer tends to travel at an almost constant speed. Next comes a transitional layer called the thermocline, in which temperature drops steadily with depth; as temperature falls, so does the speed of sound. E The U.S. Navy was quick to appreciate the usefulness of low-frequency sound and the deep sound channel in extending the range at which it could detect submarines. In great secrecy during the 1950s, the U.S. Navy launched a project that went by the code name Jezebel; it would later come to be known as the Sound Surveillance System (SOSUS). The system involved arrays of underwater microphones, called hydrophones, that were placed on the ocean bottom and connected by cables to onshore processing centers. With SOSUS deployed in both deep and shallow waters along both coasts of North America and the British West Indies, the U.S. Navy not only could detect submarines in much of the northern hemisphere, it also could distinguish how many propellers a submarine had, whether it was conventional or nuclear, and sometimes even the class of sub. F The realization that SOSUS could be used to listen to whales also was made by Christopher Clark, a biological acoustician at Cornell University, when he first visited a SOSUS station in 1992. When Clark looked at the graphic representations of sound, scrolling 24 hours a day, every day, he saw the voice patterns of blue, finback, minke, and humpback whales. He also could hear the sounds. Using a SOSUS receiver in the West Indies, he could hear whales that were 1,770 kilometers (1,100 miles) away. Whales are the biggest of Earth’s creatures. The blue whale, for example, can be 100 feet long and weigh as many tons. Yet these animals also are remarkably elusive. Scientists wish to observe blue time and position them on a map. Moreover, they can track not just one whale at a time, but many creatures simultaneously throughout the North Atlantic and the eastern North Pacific. They also can learn to distinguish whale calls. For example, Fox and colleagues have detected changes in the calls of finback whales during different seasons and have found that blue whales in different regions of the Pacific ocean have different calls. Whales firsthand must wait in their ships for the whales to surface. A few whales have been tracked briefly in the wild this way but not for very great distances, and much about them remains unknown. Using the SOSUS stations, scientists can track the whales in real time and position them on a map. Moreover, they can track not just one whale at a time, but many creatures simultaneously throughout the North Atlantic and the eastern North Pacific. They also can learn to distinguish whale calls. For example, Fox and colleagues have detected changes in the calls of finback whales during different seasons and have found that blue whales in different regions of the Pacific Ocean have different calls. G SOSUS, with its vast reach, also has proved instrumental in obtaining information crucial to our understanding of Earth’s weather and climate. Specifically, the system has enabled researchers to begin making ocean temperature measurements on a global scale—measurements that are keys to puzzling out the workings of heat transfer between the ocean and the atmosphere. The ocean plays an enormous role in determining air temperature—the heat capacity in only the upper few meters of ocean is thought to be equal to all of the heat in the entire atmosphere. For sound waves traveling horizontally in the ocean, speed is largely a function of temperature. Thus, the travel time of a wave of sound between two points is a sensitive indicator of the average temperature along its path. Transmitting sound in numerous directions through the deep sound channel can give scientists measurements spanning vast areas of the globe. Thousands of sound paths in the ocean could be pieced together into a map of global ocean temperatures and, by repeating measurements along the same paths over times, scientists could track changes in temperature over months or years. H Researchers also are using other acoustic techniques to monitor climate. Oceanographer Jeff Nystuen at the University of Washington, for example, has explored the use of sound to measure rainfall over the ocean. Monitoring changing global rainfall patterns undoubtedly will contribute to understanding major climate change as well as the weather phenomenon known as El Nino. Since 1985, Nystuen has used hydrophones to listen to rain over the ocean, acoustically measuring not only the rainfall rate but also the rainfall type, from drizzle to thunderstorms. By using the sound of rain underwater as a “natural” rain gauge, the measurement of rainfall over the oceans will become available to climatologists.

Moving in orbit around our Sun are millions of rocks known as asteroids. Now scientists have plans to capture one. A Send a robot into space, catch an asteroid and bring it back to Earth's orbit. This, say scientists and engineers at the California Institute of Technology (Caltech), could be feasible. A four-day workshop was dedicated to investigating the feasibility of capturing a near-Earth asteroid, bringing it closer to our planet and using it as a base for future manned space-flight missions. This is not something the scientists are imagining could be done someday in the future. It is possible with the technology we have today and could be accomplished within a decade. A robotic probe could anchor to an asteroid with simple magnets or grab it with specialised claws. Alternatively, a large spacecraft could use its gravitational field to shift the orbit of a larger asteroid, sending it towards Earth. 'Once you get over the initial reaction - You want to do what?! - it actually starts to seem like a reasonable idea,' says engineer John Brophy, who helped organise the workshop. In fact, many of these ideas have been on the drawing board for years as part of NASA's planetary-defence programme against large space-based objects that might threaten Earth. And there's no shortage of potential targets: NASA estimates there are 19,500 asteroids at least 100 metres wide within 45 million kilometres of Earth. B Though rearranging the heavens may seem an excessive undertaking, this US mission has its merits. The US already has plans to send astronauts to a near-Earth asteroid, a mission that would mean confining them in a tiny capsule for three to six months and would involve all the risks of a deep-space voyage. Instead, robots could bring an asteroid close enough for them to get there in just a month. An asteroid would provide a stationary base from which to launch missions further into space. There are several advantages to this. For one, launching missions carrying materials from Earth requires a lot of power, fuel and, consequently, money, because of our planet's strong force of gravity. Since this would be far weaker on an asteroid, materials mined there could be more easily taken off the asteroid and shuttled around the solar system. Many asteroids have a lot to offer. Some are rich in metals, which can be mined and used to build space-based habitats, or brought back to Earth. Others are up to one-quarter water, which could be used for life-support or broken down into hydrogen and oxygen to make fuel. Astronomers would also have the chance to get a close-up look at one of the solar system's earliest relics, generating important scientific data. 'Executing the asteroid-retrieval plan would help demonstrate and greatly expand mankind's space-based engineering capabilities,' says engineer Louis Friedman, another co-organiser of the Caltech workshop. For instance, the mission would teach engineers how to capture an unco-operative target, which could be useful practice for planetary-defence missions in the event of a threat from a meteoroid or comet approaching our planet, he adds. C Former astronaut Rusty Schweickart, co-founder of the B612 Foundation, an organisation dedicated to protecting Earth from asteroid strikes, points out that although it would be technically feasible, shifting such a hefty and substantial target would not be easy: 'You're moving the largest mother-lode imaginable,' he says. Engineers would need to be absolutely certain they could control such a potentially dangerous object. 'It's the opposite of planetary defence; if you do something wrong you have a Tunguska event,' says engineer Marco Tantardini from the Planetary Society, referring to the powerful 1908 explosion above a remote Russian region thought to have been caused by a meteoroid or comet. D Still, these obstacles only add to the appeal of the project for engineers, who love to go over every potential difficulty in order to solve it. And if the challenges posed by a large asteroid seem too daunting, researchers could always start with a smaller asteroid, perhaps two to ten metres across. Last year, Brophy helped conduct a study to look at the feasibility of bringing a two-metre, 1,000-kilogram asteroid—of which there might conceivably be millions—to the International Space Station. The study suggested the asteroid could be captured robotically in something as simple as a large bag. Of course, such a small object might not have the same emotional impact as a larger target. 'NASA isn't going to want to go to something that is smaller than our spaceships,' says engineer Dan Mazanek from NASA's Langley Research Center. E No matter the size of the asteroid, these plans would require hefty investments. Even capturing a small asteroid would consume at least a billion dollars. Convincing taxpayers to foot such a bill could be difficult. However, private industry might be interested in getting involved. One possibility would be to push the asteroid into near-Earth orbit and then invite anyone who wants to develop the capabilities to reach and mine the object. However, although the undertaking might be scientifically exciting and provide great insight into the solar system's formation, this is not enough on its own to justify the expense of bringing an asteroid to Earth. Investigations of asteroids can be done much more cheaply with an unmanned spacecraft, says chemist Joseph A. Nuth from NASA's Goddard Space Flight Center. According to Brophy, ultimately we would be working towards bringing an asteroid closer to Earth in order to help humanity move out into the solar system.

List of Headings i The need for skill and care ii Choosing the richest asteroid iii The safest way to protect an asteroid iv Obtaining support for the project v An achievable goal, not an impossible dream vi The need for global cooperation vii Beginning with a less challenging task viii Practical, economic and research justifications

List of statements A A mistake could have serious consequences for Earth. B It might be difficult to arouse interest in an asteroid of limited size. C The project could be an early step in space exploration. D An asteroid's weight makes the project extremely challenging. E The skill gained could save Earth from future danger. F An asteroid could be a useful landing place for a spaceship. G Capturing an asteroid would not be an efficient method of research.

The merits of the US mission Capture of an asteroid would reduce the time that astronauts travelling to it needed to spend in space. An asteroid could also act as a 23 _________ for further space travel and exploration. The fact that an asteroid would have weaker 24 _________ would allow easier movement of resources. These resources include 25 _________ which could be used in space or on Earth, and 26 _________ which consumed or used as a source of power. The mission could provide data on the history of our Sun and planets. It could also be good practice if there was a threat to Earth from a body from space.

Plants need to produce more individuals of their own kind, and these normally grow best from their parent. So plants need to travel, and they do so in a variety of ways. In an English woodland, the blackberry puts out exploratory stems, which curve upwards, waving slowly as though searching. If they touch another plant, they begin to advance directly and purposefully. To us, their motion is invisible, but for a plant it's an extraordinary rate—around five centimetres a day. When a stem makes contact with the ground, it puts down small rootlets, and starts to extract nutriment. The silverweed is equally effective, putting out travelling stems that advance horizontally, creeping at low level through the mat of rootlets and dead vegetation formed by other plants. In meadows, fescue grass is notable for annexing land from other less robust and aggressive species. The genetic fingerprints of its leaves and stems taken two hundred metres apart have proved, in some instances, to be identical. This must mean that one particularly vigorous plant has increased its territory year after year until now, after perhaps a century, it has become the largest plant in the entire meadow. The bird-cage plant grows among sand dunes, in the deserts of the American west, and puts down long roots to search for water. But if the sand blows away, the plant's roots may shrivel up, the plant dies, and the stems form a hollow sphere. With no roots to anchor it, the wind blows it across the sand for several kilometres. Eventually it rolls into a sheltered site, allowing the seeds inside to germinate. A few plants don't need external assistance to distribute their seeds. The Mediterranean squirting cucumber fills with a slimy juice as it ripens. Eventually the juice shifts so violently that the cucumber bursts off its stalk and shoot five or six metres through the air, leaving a trail of slime and seeds behind it. One of the most dramatic detonating seed-containers belongs to a Brazilian tree known as monkey's dinner-bell. The side of the seed pod facing the sun dries out, causing an explosion which can hurl the seeds over twelve metres. The bang is enough to convince nervous strangers in the forest that they're under attack. It's particularly important for trees that their seeds move far enough away to gain adequate light and nutriment. This is helped by the height of the tree, and in some cases by fitting their seeds with wings. Sycamore seeds, for instance, have a single wing, sprouting from one side. This makes the seed spin, and even in a light breeze, these tiny spinning helicopters can land far from their parent. Instead of using wind or water as carriers, many plants use animals. The South African grapple plant, a low-growing creeper, relies on its seeds being trodden on. Its seed capsules have arms ending in hooks that are so sharp and strong, and point in so many directions, that when the foot of an elephant or rhino descends on one, the capsule becomes attached, and is carried by the animal. Other plants reward their carriers instead of hurting them. Many plants that grow in the heathland of South Africa provide their seeds with an edible covering which ants find particularly attractive. These collect the seeds and carry them down to their underground nests, where they eat the covering, leaving the seeds themselves in an ideal position to germinate. Fruit seeds are completely enclosed with such a generous edible reward that the animal-carrier is encouraged to swallow both together. While the plant is constructing the seeds, the flesh of the unripe fruit is sour, and animals learn not to eat it. But once the seeds are fully developed, the sap becomes sweet, and the fruit signals the fact that the seeds are now ready for transport by changing colour. Animals understand the signals well. They now eat the fruit, and carry the seed away inside their stomachs, to be ejected at a distance. Not all seeds have to pass through the entire digestive tract to be transported, though. The quetzal, a Central American bird, feeds on the wild avocado, swallowing it whole. It eventually regurgitates the stone, which then has a chance to take root and produce a new plant. Passage through an animal's gut is essential for some seeds, however. When the acacia of East Africa produces its seed-bearing pods, beetles fly in, lay eggs, and as the grubs hatch, they feed on the acacia seeds. The seeds can only grow if an elephant, or other animal, eats the pod, as its digestive juices kill the eggs. Eventually the seeds return to the outside world in the animal's droppings, and can germinate. While the seeds of pine trees are developing, they're protected inside cones. When the seeds are ripe, one bird, the nut-cracker, is particularly skilful at picking them out. Those it can't eat immediately it buries, providing the seed with ideal growing conditions. But two out of every three seeds that the bird buries, it never finds again, so the tree uses a strategy of sacrificing a few of its seeds and relying on the poor memory of the courier who takes and conceals them. So in one way or another, many seeds reach destinations where they can start their lives away from the environmental dominance of their parents.

A can dominate its surroundings with a single plant. B explodes as a result of internal pressure. C has seeds which have a feature that increases the distance they travel. D colonises a new spot when it can no longer survive in another. E moves along close to the ground. F produces a loud noise when it distributes its seeds. G relies on human activity to distribute its seeds. H requires water every day. I produces branches that spread out very quickly into the air.