Challenger expedition

The Challenger expedition of 1872–1876 was a scientific programme that made many discoveries to lay the foundation of oceanography. The expedition was named after the naval vessel that undertook the trip, .

The expedition, initiated by William Benjamin Carpenter, was placed under the scientific supervision of Sir Charles Wyville Thomson—of the University of Edinburgh and Merchiston Castle School—assisted by five other scientists, including Sir John Murray, a secretary-artist and a photographer. equipping it with separate laboratories for natural history and chemistry. The expedition, led by Captain George Nares, sailed from Portsmouth, England, on 21 December 1872. Other naval officers included Commander John Maclear. However, it was the first scientific expedition to take pictures of icebergs. They collected plankton samples and recorded the speed and direction of ocean surface currents. Samples were preserved in brine or alcohol, or dried, then brought to Europe and distributed to various experts to analyse.

Preparations

To enable it to probe the depths, 15 of Challenger 17 guns were removed and its spars reduced to make more space available. Laboratories, extra cabins and a special dredging platform were installed.

Because of the novelty of the expedition, some of the equipment was invented or specially modified for the occasion. It carried of Italian hemp rope for sounding.

Expedition

thumb|upright|One of the original boxes containing the photographic negatives brought back from the expedition

On its landmark journey circumnavigating the globe, By the end of the voyage, this had been reduced to 144 due to deaths, desertions, personnel being left ashore due to illness, and planned departures.

After leaving the Cape Verde Islands in August 1873, the expedition initially sailed south-east and then headed west to reach St Paul's Rocks. From here, the route went south across the equator to Fernando de Noronha during September 1873, and onwards that same month to Bahia (now called Salvador) in Brazil. The period from September to October 1873 was spent crossing the Atlantic from Bahia to the Cape of Good Hope, touching at Tristan da Cunha on the way.

A second important issue concerning the collection of different kinds of physical data on the ocean floor was the laying of submarine telegraph cables. Many transoceanic cables were being laid in the 1860s and 1870s and their efficient laying and operation were matters of great strategic and commercial importance. Upon the retrieval of a dredge or trawl, Challenger crew would sort, rinse, and store the specimens for examination upon return. The specimens were often preserved in either brine or alcohol. Manganese nodules and sediment, which was later found to contain micrometeorites, was collected from the ocean floor.

The primary thermometer used throughout the Challenger expedition was the Miller–Casella thermometer, which contained two markers within a curved mercury tube to record the maximum and minimum temperature through which the instrument traveled. Several of these thermometers would be lowered at various depths for recording. However, this design assumed that the water closer to the surface of the ocean was always warmer than that below. During the voyage, Challengers crew tested the reversing thermometer, which could measure temperature at specified depths. Afterwards, this type of thermometer was used extensively until the second half of the 20th century. William Dittmar of Glasgow University established the composition of seawater. Murray and Alphonse François Renard mapped oceanic sediments.

Thomson believed, as did many adherents of the then-recent theory of evolution, that the deep sea would be home to "living fossils" long extinct in shallower waters, examples of "missing links". They believed that the conditions of constant cold temperature, darkness, and lack of currents, waves, or seismic events provided such a stable environment that evolution would slow or stop entirely. Louis Agassiz believed that in the deeps "we should expect to find representatives of earlier geological periods." Thomas Huxley stated that he expected to see "zoological antiquities which in the tranquil and little changed depths of the ocean have escaped the causes of destruction at work in the shallows and represent the predominant population of a past age." Nothing of the sort came to pass, however; though a few organisms previously regarded as extinct were found and cataloged among the many new discoveries, the harvest was typical of what might be found in exploring any equivalent extent of new territory. Furthermore, in the process of preserving specimens in alcohol, Thomson and chemist John Young Buchanan realised that he had inadvertently debunked Huxley's prior report of Bathybius haeckelii, an acellular protoplasm covering the sea bottoms, which was purported to be the link between non-living matter and living cells. The net effect was a setback for the proponents of evolution. As shown by later expeditions using modern equipment, this area represents the southern end of the Mariana Trench and is one of the deepest known places on the ocean floor.

Modern soundings to have since been found near the site of Challengers original sounding. Challengers discovery of this depth was a key finding of the expedition in broadening oceanographic knowledge about the ocean's depth and extent; the depression, the Challenger Deep, now bears the name of the vessel and its successor, HMS Challenger II, which in 1951 identified a depth of 5,944 fathoms nearby. Thomas Gaskell, the Chief Scientist on HMS Challenger II, observed that the later measurement<blockquote>was not more than 50 miles from the spot where the nineteenth-century Challenger found her deepest depth [...] and it may be thought fitting that a ship with the name Challenger should put the seal on the work of that great pioneering expedition of oceanography.</blockquote>The expedition also verified the existence of the Mid-Atlantic Ridge extending from the southern hemisphere to the northern one. Specimens brought back by Challenger were distributed to the world's foremost experts for examination, which greatly increased the expenses and time required to finalize the report. The report and specimens were displayed at the British Natural History Museum from January to July, 2023. Some specimens, many of which were the first discovered of their kind, are still examined by scientists today.

A large number of scientists worked on categorizing the material brought back from the expedition including the paleontologist Gabriel Warton Lee. George Albert Boulenger, herpetologist at the Natural History Museum, named a species of lizard, Saproscincus challengeri, after Challenger.

Before the Challenger expedition, oceanography had been mainly speculative.

Challenger expedition

Preparations

Expedition

References

Further reading

External links