Challenger Expedition

In December 1872, HMS Challenger left Portsmouth on a voyage that would last more than three years and cover roughly 70,000 nautical miles. The Challenger expedition was the first major scientific cruise devoted entirely to studying the deep sea, and its results gave birth to oceanography as a modern discipline. Though the ship sailed around the world, its true aim was to look down rather than out: to find out what lay beneath the surface of the oceans.

The expedition grew out of mid-nineteenth-century curiosity about the deep. Earlier dredging and sounding work, including surveys for laying transatlantic telegraph cables, had shown that the seabed was not flat or empty, and some naturalists argued that life could exist at great depths. The Edinburgh naturalist Charles Wyville Thomson and the physician and naturalist William Carpenter pressed the Royal Society and the British Admiralty to support a larger effort. The Admiralty lent a steam-assisted warship, a wooden corvette, which was refitted with laboratories and winding gear, and most of its guns were removed to make room.

Thomson led the scientific staff, which included the naturalists John Murray and Henry Moseley, the chemist John Buchanan, and the artist John James Wild. Captain George Nares commanded the ship at first. The vessel crossed the Atlantic, visited the Cape of Good Hope, Australia, New Zealand, and Pacific islands, rounded Cape Horn, and returned via the South Atlantic, reaching Britain in May 1876. Along the way the crew took soundings, dredged the sea floor, measured temperatures at different depths, and collected water and sediment samples at hundreds of stations. In the western Pacific they sounded the Mariana Trench, and the deep reading they recorded there marked the Challenger Deep, which still bears the ship's name.

The harvest was enormous. The scientists described thousands of species previously unknown to science, including many deep-sea organisms, which undermined the older belief that the abyss was lifeless. They mapped the distribution of seafloor sediments, found manganese nodules on the ocean bottom, and gathered evidence of a submarine ridge running through the Atlantic. Their temperature and chemical data helped establish how the oceans are structured and circulate.

Publication took far longer than the voyage. After Thomson's death in 1882, John Murray oversaw the editing, and the Challenger Report eventually filled about fifty large volumes, completed in 1895. It became a foundation for marine biology, geology, and physical oceanography, and it set a model for later national expeditions. Historians sometimes note that the expedition also reflected the imperial reach of the Royal Navy, but its lasting legacy is the evidence it gave that the deep sea was a vast, varied, and knowable part of the planet.