For three and a half long, dreary years the crew spent day after day dredging, measuring, and probing the oceans. Although the data they collected was scientifically indispensable, men were driven to madness by the tedium, and some sixty souls ultimately opted to jump ship rather than take yet another depth measurement or temperature reading. One day in 1875, however, as the crew were "sounding" an area near the Mariana Islands in the western Pacific, the sea swallowed an astonishing 4,575 fathoms (about five miles) of measuring line before the sounding weight reached the floor of the ocean. The bedraggled researchers had discovered an undersea valley which would come to be known as the Challenger Deep. Reaching 6.78 miles at its lowest point, it is now known to be the deepest location on the whole of the Earth. The region is of such immense depth that if Mount Everest were to be set on the sea floor at that location, the mighty mountain's peak would still be under more than a mile of water.
Nothing was known of what organisms and formations might lurk at such depths. Many scientists of the day were convinced that such crevasses must be lifeless places considering the immense pressure, relative cold, total lack of sunlight, and presumed absence of oxygen. It would be almost a century before a handful of inventors and explorers finally resolved to go down there and take a look for themselves.
The first scientist with the know-how and wherewithal to seriously consider a dive to the bottom of the Mariana was Auguste Piccard, a Swiss professor, physicist, and inventor of some repute. In the early 1930s, he had gained considerable scientific fame by constructing and piloting the world's first manned stratospheric balloon, using a pressurized sphere and helium gasbag of his own design to reach altitudes than no human had previously attained. From over 70,000 feet, he conducted experiments to measure cosmic rays, and made measurements to help prove the theories of his friend Albert Einstein. Piccard's wife--mortified that a middle-aged man would repeatedly subject himself to such risks--insisted that he retire his ballooning career. Much to her surprise, he agreed.
It turned out that he had grander plans afoot. Piccard had realized that a variation of his stratospheric balloon concept could be used as a deep-sea diving apparatus, and he soon set to work constructing his first bathyscaphe vehicle. The contraption consisted of a high-pressure passenger sphere suspended beneath a different kind of gasbag--a steel float chamber filled with gasoline. Gasoline is much lighter than water, causing it to be buoyant; yet it does not compress as air would, which allowed the tank to resist crushing even at extreme depths. The bathyscaphe operated a bit like an underwater zeppelin: operators descended by using pumps to replace small portions of gasoline with seawater, thereby reducing buoyancy. To ascend, operators used controls to let loose some of the onboard iron pellets used as ballast, thereby increasing buoyancy. Small electric propellers provided horizontal navigation.
On 23 January 1960, two men clambered aboard the Trieste for its attempt to dive into the Challenger Deep of the Mariana Trench: marine specialist Lieutenant Don Walsh of the US Navy; and oceanographer Jacques Piccard, son of the vehicle's inventor. At 76 years of age, Auguste himself was unable to take part personally. The two hydronauts were expected to be confined in their battery-powered pressure sphere for over eight hours, including almost four hours each for the seven-mile descent and re-ascent. Since no manned or unmanned vessel had ever braved the journey to the Challenger Deep, no one was sure how much life, if any, would be found there. Most scientists were reasonably sure that microorganisms would be found, but some thought it unlikely that vertebrates could withstand such an inhospitable environment.
Partway into their long descent, Walsh and Piccard grew alarmed when they discovered they were no longer able to raise the mother ship on the sonar/hydrophone communication system, even after repeated attempts. The two men were thus left truly isolated from the outside world. Curled up in the cramped, cold, and dimly-lit sphere, the adventurers continued their hours-long downward journey with only one another's voices and the occasional pop or groan from the Trieste's strained hull to punctuate the anxious silence.
At approximately four hours into their descent--several thousand feet above the sea floor--a sharp clang sounded through the pressure sphere and the vehicle shuddered violently. Once their wincing subsided, the men did what they could to inspect the craft and its condition. It seemed that the water pressure at this never-before-encountered depth--six tons per square inch--had cracked the outer pane of the lucite window. For the moment the vehicle itself remained watertight, but the damage was worrisome. The Trieste was outfitted with a few safety systems; for instance, the ballast doors were held closed by electromagnets, so in the event of electrical failure the doors would fall open and drop the ballast, causing the vehicle to rise to the surface. But such systems would be of no help to the men inside if the 1,000 atmospheres of pressure crushed their delicate passenger compartment. Moreover, no other vehicle in existence was capable of reaching such depths, which meant that if her float tank became compromised there was no chance of rescue. Nevertheless, the stalwart scientists opted to press on.
Walsh and Piccard attempted to use the sonar/hydrophone handset again, and found that it had inexplicably regained function. They reported their arrival and observations to the mother ship, and although their voices took approximately seven seconds to cross the seven miles of water, they came through quiet yet clear. The hydronauts observed the "diatomaceous ooze" through their tiny, cracked window, shivering in the 45F degree cold and munching chocolate bars to regain lost calories. For the most part, the few organisms they observed were little different from those found in the miles of water above them. Thirty or so minutes later, concerned that the damaged lucite porthole would not withstand the pressure indefinitely, the men dumped two tons of iron ballast and the vehicle slowly began to rise. Three and a quarter uneventful hours later, the bathyscaphe Trieste bobbed to the Pacific surface, having entered the history books with a record that could never be bested. Walsh and Piccard had been to the abyss and back.
Later the same day, the US Department of Navy issued a press release boasting that "the United States now possesses the capability for manned exploration of the sea down to the deepest part of its floor." Project Nekton was a success. Jacques Piccard and Lt. Don Walsh were flown to Washington DC to receive decorations from President Eisenhower, and to retell the story of their descent of alternating boredom and terror.
For a few years the Trieste continued her career as a diving vehicle, though never again to such depths as the Challenger Deep. Most of her later missions were pedestrian by comparison, although when the nuclear submarine USS Thresher was lost at sea in 1963 she did participate substantially in the search efforts. Soon thereafter she was retired, and many of her systems were incorporated into other dive vehicles. Much of her outer hull was left intact, however, and it is currently on exhibit at the Navy Museum in Washington, DC. In the 45 years since the Trieste was taken out of service, there has not been another manned dive vehicle capable of reaching the floor of the Mariana.
Even today, less than 5% of the Earth's oceans have been explored by humans according to the US National Oceanic and Atmosphere Administration. Of course humanity has not entirely abandoned the exploration of the deep. In 1995 a robotic probe did finally revisit the faraway floor of the Mariana trench, as did another such probe in 2009. Though we must not diminish the achievements of those plucky remote-controlled explorers, it seems a shame that no humans have ever attempted to return. There are some people who say that there is little value in sending humans to harsh places where hardier robotic proxies can go in their stead; but for the indefatigable adventurer, that sort of stick-in-the-mud, stay-at-home complacency is unfathomable.
Update 25 March 2012: Famed Hollywood director James Cameron has since become the third human to visit Earth's deepest chasm. He's like the Pete Conrad of the Mariana.