An Historical Perspective of Oceanography
Though the oceans cover about 71 percent of Earth's surface, until comparatively recently they remained largely unexplored. An impediment to early European exploration of the oceans was the difficulty for sailors to accurately determine their position. Though latitude can be estimated relatively easily using the angle between the horizon and the North Star, determining longitude while at sea presented a significantly greater challenge. In the 18th century, it was recognized that longitude can be expressed as a function of time, since the earth rotates 360 degrees in 24 hours. The remaining challenge was to develop an accurate, portable clock that could withstand the extreme forces and weather at sea; in 1760 John Harrison created such a clock.
In 1872, the British launched the HMS Challenger on the first major expedition to systematically collect oceanographic data. The expedition took 3 1/2 years and covered over 65,000 nautical miles. The Challenger obtained soundings to over 12,000' depth, measuring the water temperature at various depths, and surface currents. Among the many discoveries made during this voyage was the carbonate compensation depth, manganese nodules, the Puerto Rico Trench, and indirectly observed the sinking of the Antarctic Intermediate Water.