The Beginning of Deep-sea Exploration
The knowledge we currently have about the deep ocean has been a long time coming. The exploration of the deep ocean floor began in 1856, with the laying of the first telegraph cable across the Atlantic Ocean. To lay the cable correctly, it was necessary to make detailed depth measurements of the sea floor along the cable's 3,200-kilometer (2,000-mile) route between Newfoundland and the southwest corner of Ireland. These readings were made with a sounding line, a strong, thin cord with a heavy sinker at one end. The line was marked at regular intervals, like a giant measuring tape, to indicate depth.
The first major oceanographic expedition—for the sake of science rather than for commercial or military purposes—was made by the British naval ship HMS Challenger. From 1872 to 1876, the Challenger sailed the Atlantic, Pacific, Antarctic, and southern Indian oceans. Its scientists took water temperature readings at various depths, collected water for chemical analysis, dredged up samples of deep-sea sediment, much of it rich in plant and animal life, and made numerous soundings. The Challenger's voyage aroused interest in deep-sea exploration, and in the following years several countries, including Germany and the United States, launched oceanographic expeditions.