How the Challenger Expedition Shaped the Science of Oceanography

On the occasion of the publication of the findings of the Challenger expedition in 1895, the chief scientist John Murray summed up the significance by calling it “the greatest advance in the knowledge of our planet since the celebrated discoveries of the fifteenth and sixteenth centuries”.

He was certainly not modest about it. Recall that Isaac Newton only described himself as a child playing with pebbles on the beach with a vast ocean of knowledge undiscovered before it. But the Challenger mission did indeed represent something new in human affairs. It appears to be the first time that a massive state sponsored effort was put into the task of science. Not to conquer nations, appropriate lands or subjugate peoples. It was simply to face the great unknown of the ocean and wrestle some of its secrets. The ramifications of the Challenger expedition stretch far and wide, and are not limited to oceanography.

The broad statistics of the expedition speak for themselves. It involved a circumnavigation of the globe that lasted four years (1872-76), covering a distance of 127,000 km. It set out with a crew of 243 that included six senior scientists. It sampled the ocean at 362 stations, made ocean depth soundings at 492 points and dredged the ocean floor at 133 locations. The accumulated findings were eventually published in 50 volumes covering 30,000 pages, and took 23 years to compile. If size alone counted, then Murray’s claim certainly has some substance.

Among the concrete findings is included the first ever rough map of the ocean floor. The ocean floor turned out to be just as interesting as the continental surfaces, probably even more so. It contained mountain ranges that eclipsed those on dry land, both in terms of height and spread. It turned out that the islands were only the peaks of submerged mountains, and from which accounting Hawaii’s Mauna Kea would be a whole kilometer taller than Mount Everest. There were also gorges that made the Grand Canyon look like a mere pinprick. The Challenger discovered an enormous depression in the north-west Pacific Ocean representing the deepest places in the Earth’s crust. Now called the Mariana trenches, the deepest point in it is named the Challenger Deep in honor of the expedition.

Other surprises included the fact that the ocean floor consisted largely of basalt rock, contrasted with the granite that made up the continents. In fact, it appeared that the continental granite was floating on the heavier basalt, together making up the crust of the Earth.

Also revealed for the first time was ocean currents, enormous bodies of water flowing through the ocean as if rivers. Temperature and salinity readings at various depths also revealed the existence of convection currents. Far from being a stagnant pond, it appeared that the ocean was being churned vertically. This ensured that oxygenated water reached the lowest depths allowing for the existence of life there. As for marine species, the naturalists on board identified 4700 new ones.

But the greatest achievement of the Challenger expedition was to establish the science of oceanography on a secure footing. The concrete findings turned out to be the clues that led to greater discoveries. In this sense, the greatest discovery of the expedition would be that of the Mid-Atlantic ridge, a mountain chain extending the entire length of the Atlantic Ocean near its center. It was later found that the ridge contained a central depression from which new rock was emerging from the mantle beneath. This led to Alfred Wegener’s theory of continental drift, and ultimately the plate tectonic theory.

The boldness and the scope of the venture also served as the impulse to further scientific expeditions carried out by other nations. The German ship Meteor set out on a 3 year expedition in 1925 using echo sounding techniques to map the ocean floor. Most significantly it found that the Mid-Atlantic ridge extended below Africa and into the Indian Ocean. Further expeditions in the 1950s, aided by satellites, led to the revelation that the Mid-Atlantic ridge was only a part of a global rift. These expeditions were modeled on the scope of the Challenger’s and led to rapid developments in the knowledge of tides, ocean bulges, marine geology and marine life.

It is also interesting to note that the techniques used in the Challenger expedition are, by and large, still those employed by oceanographers today. Dredging, sampling, and trawling are now standard, though of course the equipment is far more sophisticated today. Ocean sounding has become far easier with radar; it was done on the Challenger using hemp rope and sending a weight to the ocean floor, using a steam-powered pump of 12 horsepower. There was over 144 miles of rope aboard the ship.