Deep-Sea Exploration: The HMS Challenger Expedition
Deep-Sea Exploration: The HMS Challenger Expedition
The HMS Challenger, a 200-foot warship converted for scientific use, left the English port of Sheerness on December 7, 1872, for a four-year voyage of exploration. Unlike previous expeditions, Challenger left to explore the sea itself, the first scientific expedition of oceanographic exploration. During Challenger's four years away from home, her crew and scientists founded the era of modern scientific study of the ocean and its creatures. Challenger returned to England on May 24, 1876, having traveled 68,890 nautical miles (79,277 miles or 127,584 km) with scientific specimens from over 350 sampling locations. These specimens included samples of bottom materials, samples of bottom animal life, water samples at a variety of depths, and samples of aquatic life from various depths. In addition, seawater temperature at different depths was measured, as were surface weather conditions, measurements of ocean currents, and other information. Following her return, a total of 50 volumes of scientific reports were published by a team of over 100 scientists that described and explained the voyage's findings. The voyage was said to have been "the greatest advance in the knowledge of our planet since the celebrated discoveries of the 15th and 16th centuries."
The great age of exploration and discovery that began with the Portuguese and Spanish in the fifteenth century had largely run its course by the latter part of the nineteenth century. All the major landmasses of the world had been discovered by that time, the coastlines charted, and explorers were making major inroads towards exploring the continental interiors for geographic, scientific, and commercial purposes. Throughout this time the oceans served as highways between nations and continents, highways upon which ships sailed carrying raw materials, finished goods, people, and money from port to port. Fishermen, whalers, sealers, and others depended on the sea for their livelihood, and the products of their work fed and employed countless people in nearly every country. Yet, in spite of this dependence on the oceans, no systematic scientific study had been made of them until the Challenger set sail in 1872.
Although explorations on land were progressing well, land encompasses only about 30% of the Earth's surface. No matter how thoroughly the continents were mapped and explored, there was a limit to our understanding of the Earth unless serious, scientific exploration of the oceans took place. This is the role that Challenger,under the scientific direction of Charles Wyville Thomson (1830-1832) and the military leadership of Captain George Nares (1831-1915) was to fill.
The Challenger voyage was a logical progression from other scientific voyages sponsored by Britain. Captain James Cook (1728-1779) made three voyages of discovery with the Endeavour between 1768 and his death in 1779, Charles Darwin (1809-1882) accompanied the Beagle in 1831 on a voyage of nearly five years, and other lesser known scientists and explorers made similar voyages. But England's empire on land was held together by her dependence on the sea. So, in 1870, Thomson, a professor of natural history at Edinburgh University, persuaded the Royal Society to recommend a voyage of oceanographic exploration and study, a recommendation that was granted.
At the time Challenger set sail, geologists were relatively certain that there were vast expanses of featureless plains at the bottom of the oceans, probably covered with all the sediments washed from the continents. They were also sure that life could not exist at the ocean bottoms and that any sediments found would likely be unremarkable, fine-grained sediments that varied little from place to place. All of these suppositions were shown to be wrong. Finally, the land-based scientists had some facts with which to work.
The major impact of the Challenger expedition was scientific in nature, but these discoveries either were staggering in and of themselves or later led to other discoveries that fundamentally changed the way in which we view our world. Some of these were:
- Discovery of undersea mountains, particularly along the Mid-Atlantic Ridge.
- Discovery of life at the bottom of the oceans.
- Charting of surface and subsurface ocean currents, salinity differences, and temperatures.
- Returning samples of sea-floor sediments, including manganese nodules, from a variety of locations.
From the viewpoint of long-term scientific impact, the discovery of the Mid-Atlantic Ridge is perhaps the most significant discovery made by the Challenger, though this was not appreciated until more than 80 years after the voyage. Not only did this dispel the conception of the abyssal plains as uniformly flat and featureless, but the Mid-Atlantic Ridge turned out to be crucial to understanding the concept of plate tectonics. It is there that geologists first understood how the tectonic plates upon which continents ride are formed and travel around the globe. The theory of plate tectonics, in turn, has proved to be a unifying force in the fields of geology, evolutionary biology, and climatology, among others. The presence of undersea mountains helped to validate the concept of the earth as a dynamic geologic environment, a living planet in the geological sense that mountains and islands are born, age, and are eroded away. Another discovery, a deep-sea trench 8,515 meters (nearly 27,000 feet) deep, turned out to be due to plate tectonics, too. This trench is actually a subduction zone where one plate is diving beneath another, completing the journey begun at a mid-ocean ridge such as the Mid-Atlantic Ridge.
At each observation station, the Challenger attempted to dredge the ocean floor for any animal life they could find. At first it was widely thought that no life could survive the high pressures and low temperatures at the sea floor. This notion was proved wrong when Challenger's nets brought up living creatures from the greatest depths. Finding life under such conditions led, in turn, to a reevaluation of the conditions under which life can exist, suggesting that living beings are not as fragile as previously thought. This concept has lately been taken to even greater extremes with the discovery of "extremophiles"—organisms that survive temperatures above boiling, extreme pressures, highly acidic solutions, vacuums, and extreme radiation levels. All told, Challenger scientists discovered over 4,700 species that were new to science.
Adding to this already impressive legacy, Challenger also obtained a suite of samples at each observation station that gave information about water temperature, water chemistry, and current direction at a number of depths down to the ocean floor. At the same time, surface conditions were noted, including weather, the direction of surface currents, and any other information that could be gathered. The immediate impact was the start of global maps of surface currents and weather conditions. The measurements obtained at various depths set in motion studies that later led to a better understanding of the manner in which ocean and atmosphere interact to cause weather, the interdependence of ocean and climate, and the impact that changes in ocean conditions can have on terrestrial climate over longer periods of time. For example, scientists have recently discovered the intimate link between wind patterns over the Pacific Ocean and the onset of El Niño weather conditions that affect parts of Asia, the Americas, Australia, and Africa. For the first time, scientists began to understand that conditions in the oceans were not uniform, that the oceans could affect the weather (and vice versa), and that these facts could be significant scientifically, economically, and militarily.
The discovery that sea floor sediments were varied also came as a surprise to many. In fact, Challenger brought back many surprises. Parts of the sea floor were covered with large nodules that turned out to be primarily manganese and other metals. Recently, technology has been developed that will allow mining of these areas for the manganese, a process that, once started, could have significant economic impacts as well as potentially serious environmental effects on the areas of ocean that are mined. In addition, it was found that large parts of the ocean floor were covered with biogenic ooze; sediments derived mainly from microscopic shells composed of calcium carbonate and silica. In fact, in many places siliceous shells predominate because calcium carbonate dissolves. These shells helped demonstrate the major role played by microscopic organisms in the ocean ecosystem and assisted with proper identification of rocks composed of similar sediments found on land.
Like any good research, Challenger's discoveries led to as many questions as were answered. These, in turn, led to more questions as knowledge of the oceans increased, and this process continues today. As important as Challenger's discoveries were, equally important is the branch of scientific study that was thus established. Today, oceanographic exploration is a legitimate form of scientific inquiry practiced by thousands of scientists on over 100 oceanographic research vessels in all major bodies of water on Earth. All of this was started by Challenger, the first ship to purposely set out to explore the 70% of our planet covered by water.
P. ANDREW KARAM
Saari, Peggy, and Daniel B. Baker. "HMS Challenger." In Explorers & Discoverers: From Alexander the Great to Sally Ride. Detroit: UXL, 1995.
Thurman, Harold, and Alan Trujillo. Essentials ofOceanography. Englewood Cliffs, NJ: Prentice Hall, 1999.