Deep-sea exploration

Deep-sea exploration is the investigation of physical, chemical, and biological conditions on the ocean waters and sea bed beyond the continental shelf, for scientific or commercial purposes. Deep-sea exploration is an aspect of underwater exploration and is considered a relatively recent human activity compared to the other areas of geophysical research, as the deeper depths of the sea have been investigated only during comparatively recent years. The ocean depths still remain a largely unexplored part of the Earth, and form a relatively undiscovered domain.

Scientific deep-sea exploration can be said to have begun when French scientist Pierre-Simon Laplace investigated the average depth of the Atlantic Ocean by observing tidal motions registered on Brazilian and African coasts circa the late 18th or early 19th century. However, the exact date of his investigation is unknown. He calculated the depth to be 3,962 metres (12,999 ft), a value later proven quite accurate by echo-sounding measurement techniques.^[1] Later on, due to increasing demand for the installment of submarine cables, accurate measurements of the sea floor depth were required and the first investigations of the sea bottom were undertaken. The first deep-sea life forms were discovered in 1864 when Norwegian researchers Michael Sars and Georg Ossian Sars obtained a sample of a stalked crinoid at a depth of 3,109 m (10,200 ft).^[2]

From 1872 to 1876, a landmark ocean study was carried out by British scientists aboard HMS Challenger, a screw corvette that was converted into a survey ship in 1872. The Challenger expedition covered 127,653 kilometres (68,927 nmi), and shipboard scientists collected hundreds of samples and hydrographic measurements, discovering more than 4,700 new species of marine life, including deep-sea organisms.^[1][3] They are also credited with providing the first real view of major seafloor features such as the deep ocean basins.

The first instrument used for deep-sea investigation was the sounding weight, used by British explorer Sir James Clark Ross.^[4] With this instrument, he reached a depth of 3,700 m (12,139 ft) in 1840.^[5] The Challenger expedition used similar instruments called Baillie sounding machines to extract samples from the sea bed.^{[citation needed]}

In the 20th century, deep-sea exploration advanced considerably through a series of technological inventions, ranging from the sonar system, which can detect the presence of objects underwater through the use of sound, to manned deep-diving submersibles. In 1960, Jacques Piccard and United States Navy Lieutenant Donald Walsh descended in the bathyscaphe Trieste into the deepest part of the world's oceans, the Mariana Trench.^[6] On 25 March 2012, filmmaker James Cameron descended into the Mariana Trench in Deepsea Challenger, and, for the first time, filmed and sampled the bottom.^{[7][8][9][10][11]}

Despite these advances in deep-sea exploration, the voyage to the ocean bottom is still a challenging experience. Scientists are working to find ways to study this extreme environment from the shipboard. With more sophisticated use of fiber optics, satellites, and remote-control robots, scientists hope to, one day, explore the deep sea from a computer screen on the deck rather than out of a porthole.^[3]