On 23 January 1960, two men squeezed themselves into a steel ball not much bigger than a hot tub, dangling beneath a strange-looking craft floating off the island of Guam in the Pacific. The men were Swiss engineer Jacques Piccard and U.S. Navy lieutenant Don Walsh. The craft was the Trieste - a bathyscaphe, basically an underwater hot-air balloon designed by Jacques's father Auguste. They were about to try to reach the deepest place on Earth.
They began sinking into the Mariana Trench, a vast underwater canyon southwest of Guam. Down they went - 1,000 feet, 10,000 feet, 20,000 feet - into a blackness no human had ever entered. After nearly five hours they touched the muddy floor at 35,797 feet, or about 6.78 miles down. The pressure outside their tiny window was around eight tonnes per square inch - enough to crush a tank. Just as they settled, a window cracked with a loud bang. They held their breath. The hull held. Through the gloom they spotted a flatfish that gently swam past, proving life could exist even there.
They stayed on the bottom for only 20 minutes, then began the long climb up. Their dive was so deep that even today, more than 60 years later, only a tiny handful of people have ever returned - among them film director James Cameron and explorer Victor Vescovo. The trench is so remote that scientists are still discovering new species and bits of plastic litter there at the same time, a reminder of just how far our footprint already reaches.
