Exploration

The History of Exploration

Early ideas of the shape of the world were based on little more than myth and superstition. For all their brilliant astronomy, the Ancient Egyptians thought of the world as a flat square beneath a pyramid sky. But the Ancient Greeks realized there were clues to its real shape. They noticed that ships vanished over the horizon, and heard from travellers how, as they went north, new stars rose in the sky ahead and dropped out of sight behind. What better explanation could there be than that the Earth was round? Another clue to the planet's shape was provided by Greek philosopher Aristotle (384–322 BC), who observed that the Earth's shadow, as it fell on the Moon during eclipses, was round. With the fall of the Greek civilization, these ideas were largely forgotten—only Arab scholars kept them alive.

For a century, hundreds of travellers and merchants, including the great Arab traveller, Ibn Battuta, ventured between Cathay and the west. Often they travelled along what came to be known as the Silk Road, through great Mongol cities such as Samarkand. On their way home, they brought not only silk, but playing cards, porcelain, and furniture, which strongly influenced western lifestyles. They also brought new inventions such as printing, paper money, and gunpowder. The Mongol Empire collapsed in the mid-14th century, and the Silk Road was cut off.

Prevented from travelling overland, Europeans set out to reach the Orient by sea. From the early part of the 15th century, many ships sailed south from Europe, venturing further and further round the continent of Africa in sailing ships called caravels. Many of the sailors were Portuguese, sent out by Prince Henry the Navigator (1394–1460) from his base at Sagres on the southern tip of Portugal.

In 1497, Vasco da Gama (c. 1460–1524) led one of the greatest voyages of exploration in this period. With tremendous courage, he sailed thousands of miles out into the south Atlantic, round the Cape of Good Hope, up the east coast of Africa, and across the Arabian Sea and the Indian Ocean to reach Calicut in southwest India. Five years earlier, Genoese adventurer Christopher Columbus (1451–1506) had completed an even more astonishing voyage. Sailing west across the then unknown Atlantic Ocean, he had expected to reach the Indies, as south Asia was then known. Instead, he found himself on the fringing islands of an entirely new continent, soon to be named the Americas. It seems that Columbus had miscalculated, and the Indies were much further around the world than he had predicted, but his discovery was nevertheless momentous.

Columbus may not have been the first European to cross the Atlantic—the Vikings, for instance, had succeeded 500 years earlier—but his voyage had great impact. It opened up an entire New World to the Europeans, who embraced it enthusiastically. Following conquests by Spanish adventurers, such as Francisco Pizarro (c. 1476–1541) over the Incas of Peru, and Hernán Cortés (1485–1547) over the Aztecs of Mexico, thousands of Spanish pioneers settled in South America. Meanwhile, voyagers and pioneers from northern Europe explored and settled North America, beginning with John Cabot (c. 1450–1499) and his sons, who sailed from Bristol, England, in 1497. A quarter of a century later, in 1522, Ferdinand Magellan's (c. 1450–1499) ship, the Victoria, made its momentous circumnavigation of the world.

More than 100 years later, in 1642, Dutch navigator Abel Tasman (1603–1659) sailed right round Australia. But it was not until 1768 that English captain James Cook (1728–1779) took his ship, the Endeavour, to map the South Pacific and its islands, bringing them properly into the known world for the first time.

By the 18th century, most of the world's coastlines had been explored, but many continental interiors remained as dark and mysterious as ever. Sea explorers were followed by settlers, soldiers, and governors who launched expeditions inland. In North America, Daniel Boone (1734–1820) led settlers across the Allegheny Mountains and into Kentucky, and in 1804 Meriwether Lewis and William Clark found a route from the Missouri River across the Rocky Mountains to the Pacific. In Australia, Edward Eyre (1815–1901) explored the interior and discovered Lake Eyre, and William Wills and Robert Burke crossed the continent from south to north, but died on their return journey.

From the mid-19th century, Europeans such as Richard Burton (1821–1890), James Grant (1827–1892), John Hanning Speke (1827–1864), and David Livingstone (1813–73) began to explore the mysterious, unknown interior of the vast African continent. In 1858, Burton and Speke discovered Lake Tanganyika. Two years later, Speke discovered Lake Victoria, and traced the source of the River Nile. Livingstone discovered the great Victoria Falls on the Zambezi in 1856. Later, in 1867–1868, he pressed westwards from Zanzibar, and after suffering innumerable hardships found Lakes Mweru and Bangweulu.

By the end of the 19th century, the polar regions were the last great unexplored areas of the Earth. Throughout the 1800s, these vast regions of ice had held a fascination for adventurers such as Sir John Franklin (1786–1847), who travelled to the Arctic, and Sir James Clark Ross (1800–1862), who braved the cold in expeditions to the Arctic (1831) and Antarctic (1839–1843). But nobody had ventured to the North Pole and South Pole. It became a race. In 1909, Robert Peary (1856–1920) walked across the ice to the North Pole. Two years later, Roald Amundsen (1872–1928) reached the South Pole, beating Robert Scott (1868–1912).

Exploring Space

In 1781, British astronomer Sir William Herschel (1738–1822) discovered Uranus, the first new planet to be discovered since ancient times. He also discovered two moons of Uranus, Titania and Oberon, and two moons of Saturn, Mimas and Enceladus. For the first time, scientists began to realize that the solar system was much bigger than anyone had thought. Until 1838, nobody realized how far away even the nearest stars are. But that year, Friedrich Bessel (1784–1846) measured the distance to a star for the first time, using the parallax method—by measuring the slight shift in the relative position of stars as the Earth moves round the Sun. His calculations showed that the star known as 61 Cygni is an astonishing 10.3 light years (90 trillion kilometres) away. As such, it is one of the nearest stars to the Earth.

The Sun is just one of billions of stars in the cluster known as the Milky Way, visible sideways-on as a pale white strip across the middle of the night sky. Until earlier this century, the Milky Way was thought to be the entire universe. In 1912, American astronomer Henrietta Leavitt (1868–1921) discovered a method of measuring how far away distant stars are by comparing brightnesses of fluctuating stars, known as cepheid variables. Seventeen years later, astronomer Edwin Hubble (1889–1953) made a discovery which has enlarged the region known to us far more than any discovery in the entire history of exploration. Using cepheid variables viewed through a very powerful telescope, he showed that the tiny cluster of stars known as Andromeda is not part of the Milky Way at all, but a separate, equally large galaxy of stars more than a quarter of a million light-years away. He soon discovered other galaxies beyond the Milky Way. 

As telescopes have become more sophisticated, more galaxies have been revealed at greater and greater distances. It now seems that our galaxy is just one of countless millions of galaxies scattered throughout the universe, each containing hundreds or even thousands of billions of stars. In 1998, a particularly bright galaxy, known as a quasar, was spotted more than 13 billion light years away (more than 100 billion trillion kilometres away). This is so far away that the light we see beaming from it left the quasar more than 13 billion years ago—soon after the dawn of the universe—and is only just reaching us now despite travelling at 300,000 kilometres (186,000 miles) a second for all that time. Increasingly powerful means of observation, such as the Hubble Space telescope orbiting the Earth and therefore clear of the distorting effects of the atmosphere, have also allowed us to explore space nearby in increasing detail. In recent years, for instance, planets have been discovered circling other stars apart from our own Sun—and this discovery makes it increasingly likely that somewhere in the universe there is a planet that, like Earth, supports life.

The remote exploration of the universe by telescope from the Earth has gone far beyond where we can physically travel. In the last four decades, rockets have launched unmanned craft into space that are travelling farther and farther away from Earth. Following the launch of the USSR's Sputnik 1 in 1957, space milestones were reached very quickly. In 1962, US Mariner 2 flew past Venus, the first human-made object to fly by another planet. In 1965, Mariner 4 explored the surface of Mars, and in 1966, the Soviet Lunar 9 landed on the Moon. In 1970, Soviet Venera 7 landed on Venus, the first landing on another planet. Since then, space probes have flown past every known planet in the solar system except for the most distant, Pluto, not only beaming back huge amounts of data about the nature of planets such as Jupiter and Saturn, but also revealing many previously undiscovered moons circling these distant celestial bodies.

Meanwhile, after a flurry of achievements in the 1960s and 1970s, the progress of manned space exploration has been much slower. In 1961, Soviet cosmonaut Yury Gagarin (1934–1968) became the first person to travel in space. Then in 1969, American astronauts Neil Armstrong (1930– ) and Edwin Aldrin (1930– ) became the first humans to walk on the Moon. Since then, manned space flights have largely concentrated on maintaining satellites and space stations orbiting the Earth, such as the American Skylab and the Russian Mir. Sometime in the 21st century, the National Aeronautics and Space Administration (NASA) plans to send a manned mission to Mars.

Exploring the Oceans

Beebe descended in his bathysphere to a record 923 metres (3,028 feet) off one of the Bermuda islands. But his craft was not manouevrable; it could only go straight down and straight back up again. Then in 1947, Swiss engineer Auguste Piccard (1884–1962) invented a steerable version, called a bathyscaphe. In 1960, Piccard's son Jacques (1922– ), accompanied by US Navy Lieutenant Don Walsh, made an astonishing descent into the North Pacific Ocean in Trieste, a bathyscaphe designed by Auguste. They reached the bottom of the Challenger Deep of the Marianas Trench, the world's deepest known ocean trench, 11,033 metres (36,198 feet) below sea level. The danger and difficulty of the Trieste's voyage was such that it has never been repeated, and only three bathyscaphes have ever been built. The real breakthrough in ocean exploration came in the 1950s and 1960s with sonar surveys, which are based on the reflection of sound waves from the ocean floor.

When American geophysicist Maurice Ewing (1906–1974) enlisted two colleagues to create a map of the ocean floor, their research revealed a central rift valley running the length of the Mid-Atlantic Ridge. Within a few years, they had discovered that the ridge was not just a feature of the Atlantic, but was actually part of a long, submarine mountain range winding 60,000 kilometres (37,000 miles) through all of the oceans. It is the longest mountain range in the world.

By the 1960s, it had become clear that the ocean floor had a surface as rich and varied as the continents. Over the next decade, a new generation of manned submersibles, including the famous Alvin, operated by the Woods Hole Oceanographic Institution, began to make more voyages into the deep ocean. One of the most amazing discoveries was the presence of 'Black Smokers', dark chimneys on the sea floor which belch hot, mineral-rich water. These hydrothermal vents proved to be home to a unique community of organisms, possibly among the oldest life forms on Earth.

Much deep ocean exploration today is carried out by robot submersibles. Many of these are remotely operated vehicles, or 'rovs', operated by cable, such as Jason, the craft that discovered the wreck of the ship Titanic. In 1995, the Japanese rov Kaiko landed on the ocean bed at about 10,920 metres (35,799 feet) in the Challenger Deep. Remarkably, it spotted lugworms and shrimps living even at this depth.

In the future, many explorations may be performed by untethered robot craft known as autonomous underwater vehicles, or 'auvs', such as the Massachusetts Institute of Technology's Odyssey. Rovs need support ships on site constantly, but auvs can roam the ocean depths freely, without human intervention. Although they cannot yet beam back pictures instantly, auvs can search the depths, recording information for up to a year non-stop, guided by artificial intelligence. Eventually, oceanographers hope to be able to communicate directly with auvs using a system called acoustic local-area networks, or ALANs, which send messages in much the same way as a cellphone.

Just what these craft will discover remains the subject of debate among oceanographers. Some say that we have now explored 97 per cent of the ocean depth, and that there will be little new or interesting information in the remaining 3 per cent. Others think that this last 3 per cent could be crucial.

Not all oceanic discoveries in the future will be made by diving, however. Already satellites have revealed vast areas of the oceans, showing movements of currents, concentrations of chemicals, sea-surface temperatures, and the presence of plankton. In 1996, the European Space Agency's satellite ERS-1 showed that it could map the ocean floor by picking up minute variations in the height of the sea surface, reflecting variations in gravity. Where there is a mountain under the sea, its extra gravity pulls water towards it, making the ocean bulge up. A deep trench, on the other hand, causes a depression on the ocean surface. The difference can be as much as 100 metres (328 feet). It is so gradual that ships never notice it, but ERS-1 could detect it—and so could the US satellite GEOSAT, which had been launched secretly in 1978 by Pentagon, the headquarters of the US Department of Defense.

Combining the new ERS-1 data with the years of data from GEOSAT, Walter Smith of the National Oceanographic and Atmospheric Administration (NOAA) and David Sandwell of the Scripps Institute of Oceanography made a startlingly accurate map of the ocean floor. Smith and Sandwell's maps show every feature on every part of the ocean floor bigger than a hill, and the detail is improving annually.

Exploring the Earth

One reason why the nature of exploration has changed is that there are practically no unexplored places left to discover. Another is the arrival of satellite technology. Ever since satellites were first launched in space in the 1960s, we have had a complete overview of every inch of the planet. As this technology improves, we are being provided with increasingly detailed and up-to-the-minute information and images of different aspects of the Earth's surface, from infestations of particular species of plants in Tahiti to variations in Japanese crop patterns. Three systems, in particular, have helped to create the science 'geodesy', the measurement of the Earth's surface: laser ranging, the Global Positioning System (GPS); and Satellite radar interferometry (SAR).

Laser ranging depends on ground-based stations which bounce laser beams off satellites in space to another ground-based receiving station. Because laser beams are so straight, they can provide extremely accurate measurements of very long distances—to within millimetres over thousands of kilometres. Indeed, the system is so accurate that scientists have actually been able to measure the slow movement of the continents around the Earth. We now know, for instance, that South America and Africa are drifting almost 20 cm (7.9 inches) further apart every year.

The GPS relies on radio signals emitted by satellites in space and picked up by a receiver on the ground, and can pinpoint locations within, theoretically, a few centimetres, and in practice, a few metres. The number of uses of the GPS is growing by the year, and includes everything from mapping state boundaries to tracking taxis. One important geodetic use is for detecting slight movements of the Earth's surface that might indicate an imminent earthquake or volcanic eruption.

SAR uses the principle of interference—the interaction between light waves that creates the coloured fringes on patches of oil. SAR satellites such as the ERS-1 and JERS-1 make radar images of the ground by beaming down microwave signals and picking up the reflections. They make several images, each from a slightly different orbit. The tiny variations in the distance to the ground for each image mean the microwaves are slightly out of phase—and so interfere with each other when superimposed by computer. The 'interferogram' gives a 3D view of the landscape, and repeated passes of the satellite will reveal minute changes in the relief. Using this technique it is possible to make astonishingly accurate height maps of any terrain, however inaccessible or dangerous. This may be especially useful for the prediction of volcanic eruptions, since the satellite may be able to pick up even a slight swelling of the ground that might indicate an imminent eruption.

In the 21st century, satellite mapping will enable us not only to map every inch of the planet instantly and with extreme accuracy, but to detect the slightest changes. The days of exploration of the Earth's surface will be over. But the vastness of space is still almost completely unknown and unexplored.