Hidden deep beneath the waves of the western Pacific lies the Mariana's Trench, the deepest point of all the oceans. [Music] The first step on the journey of what created this mysterious scar in the Earth's crust and how it continues to mold the planet takes us back to 1872 when a British research vessel HMS Challenger set out on the first ever mission to map the ocean floor. Throughout most of recorded history, men have just assumed that beyond a certain level, the sea was pretty flat, pretty dead, fairly lifeless.
They weren't expecting to find anything very interesting. For 4 years, the Challenger crisscrossed the oceans, covering 70,000 m, a third of the distance to the moon. The crew plumbed the depths every 140 m using a total of 249 m of rope and hundreds of pounds of lead weight.
It was tedious. backbreaking work, but at the time it was the only way to measure the depth of the ocean floor. When they got to the Western Pacific, 200 m off the island of Guam, the crew routinely lowered the rope for a measurement, but the weight kept on dropping and dropping.
It's a big surprise. Nobody thought the ocean was this deep. So all of a sudden we've got scientists saying, "Why is [Music] that?
" Eventually, the weight struck the bottom at 4,475 fathoms, nearly 5 miles beneath the ocean surface. The scientists would be going, "Wow, we found something. And what does it mean?
Is it a little hole? Is it a big hole? What kind of feature is it down there?
" There's a whole lot of questions you get when you find this one spectacular reading. The Challenger expedition marked the birth of modern oceanography and provided the first crude map of the ocean floor. It showed how the ocean floor gently slopes away from the land and then plummets thousands of feet into vast flat plains.
But the Western Pacific is different. It drops off again into the 5mm deep hole. A hole that blew right out of the water the long-held belief that the seafloor was flat and featureless.
and it spawned a mystery because nobody could understand how this strange underwater feature came about. It would be 75 years before any answers emerged. It took a revolutionary new technology, sonar, to push the investigation forward to the next crucial stage.
Sonar was first developed in the early 1900s and then perfected during the 1940s to detect submarines lurking in the [Music] deep. The system works by pumping sound waves through the water. The waves bounce off solid objects and are reflected back to a detector.
By measuring the time it takes for the sound waves to bounce back, scientists realized they could build a remarkably accurate picture of the world beneath the waves. The world's major navy spend a lot of time and effort developing submarine hunting technology. Then the hydrographers discover that you can use this to chart the bottom of the sea and it's an awful lot cheaper and easier than using large numbers of sailors pulling on ropes.
In 1951, a British Navy research ship returned to the deep hole found by the Challenger expedition. But this time, they were armed with sophisticated new sonar equipment. And the results were amazing.
Detailed sonar maps revealed that the deep hole in the Pacific Ocean floor isn't a hole at all, but part of a massive trench, 30 times deeper than the Empire State Building is high. It runs twice the length of California, 1500 m from the southeast of Guam to the northwest of the Mariana Islands. People were probably astounded by what they were seeing because clearly the ocean floor had enormous changes in relief, was very mountainous in some places, had great deeps in other places.
To a geologist, this would be extremely exciting. Even within the trench itself, there are remarkable variations. At its southern end lies the greatest surprise of all.
The seafloor drops down another two miles to its lowest point, a staggering 7 miles beneath the waves. Scientists had discovered the deepest part of the oceans. Even today, it is the lowest known point on the planet.
They named this part of the trench the Challenger Deep in honor of the ship that discovered it. to get a sense of just how deep trenches are. If we take the height of Mount Everest, we would still have about a mile of water above us before we get to the ocean surface.
But how the Marian's trench was formed remained a mystery. Investigators decided the best way to find the answer was to dive to the bottom of the trench to see for themselves the lowest point on the planet, the Challenger Deep. But they faced a major problem.
At the bottom of the trench, they would have to contend with pressure a thousand times stronger than at the surface. That's the equivalent of being squeezed on all sides by the weight of 50 jumbo [Music] jets. To demonstrate the effects of such pressure, scientists use a dummy head.
Today, what we're going to do is actually put one of these styrofoam wig heads in the uh pressure chamber and expose it to the uh pressure we would see in the Mariana's Trench. That's about 16,000 PSI. A human skull would be crushed to a pulp, but the rubbery head will only have all the air squeezed out.
Wow, that's smaller. And here's what the original size was just for comparison. Quite dramatic.
Pretty stark difference between uh something that hasn't been seven miles deep in the ocean and something that has. Glad I'm not going there. At the Mariana Trench, human life is impossible.
We're not equipped to resist those kinds of pressures. And so it's necessary to protect humans from that type of an environment. The challenge to engineers was how to accomplish this.
In 1953, Swiss scientist August Picard designed the Trieste, a pioneering vehicle that could withstand the crushing pressures. The submersible was dominated by a 50-ft long hull filled with light aviation gasoline and lead weights to control buoyancy. Slung underneath it was a tiny 6-ft spherical cabin with 5-in thick steel [Music] walls.
Finally, after 7 years of modifications and manned test dives no deeper than 3 and 1/2 miles, the Trieste was ready to attempt the 7 mi to the bottom of the trench. The commander of this perilous undertaking was US Navy Lieutenant and deep sea explorer Don Walsh. I know the astronauts that go through this all the time.
Why do you have to be there? Why can't we just put up a robot to do things? Got to be there because that's what we do.
Only a few officers and scientists knew about the risky mission which was launched in January 1960 from the western Pacific island of Guam. Wong in those days was kind of a backwater. It was just right for us because we were trying to do this project sort of out of sight because we weren't too sure it was going to work.
The Navy just didn't want to be embarrassed by a failed science spectacular. Accompanying Walsh was the son of the Trieste designer, engineer and oceanographer Jacqu Peicard. The two men would spend the next 9 hours squeezed inside the cramped sphere and we had um 20 cubic feet of space inside.
That's about the same as a household refrigerator. And the temperature was almost that cold inside. It was a drama.
At a speed of just 3 mph, they began their slow descent into the twilight zone. By 3,000 ft, the darkness was total. The only illumination was from the Triest's powerful lights.
The depths we were operating at, it was always black. The only thing that lit up the abyss was the bioluminescence from animals and plankton. Like fireflies, they carry their own light sources with them.
Encased in their 5-in thick steel sphere, Walsh and Peicard quickly passed their test dive record of 18,000 ft. Everything appeared to be going to plan. At the rear of the cabin, the crew were protected by a double layer of glass, but two hours into the dive, the outer pane cracked.
We um had a great big bang. We didn't know what it was. We were about 20,000 ft.
And we looked around and checked everything. Every square inch of their tiny lifeup supporting capsule was fighting back 8 tons of pressure. With the outer pane broken, the only thing between the men and instant death was a single pane of glass.
If the inner window had cracked, um, we would have been instantly dead, maybe even before we knew it. But incredibly, the inner pain remained watertight. Walsh and Peicard decided to continue the descent.
After a tense, claustrophobic 4 hours and 48 minutes, they approached the bottom of the trench only to be startled by movement on the sea floor. Just before we landed, we saw a flat fish about a foot long, and that's a bottom dwelling fish. So, if you see one, there are others.
Nobody expected to see life at these crushing depths, but it meant the explorers had reached their [Music] goal, the very bottom of the Mariana's trench. The depth gauge with a reading of 35,800 ft nearly 7 mi below the surface confirmed the sonar findings. squeezed inside their bubble of breathable air.
The two explorers were closer to the Earth's center than man had ever been. We took a selfportrait. That's the picture that you see.
Said we're going to do it and we did it. But there was work to be done. Walsh and Peicard wanted to make detailed observations of the enormous trench.
Unfortunately, the Trieste stirred up a cloud of fine powdery sediment from the seafloor that obscured their view. It's like being in a bowl of milk at that point. So realizing we're not going to see anything, we decided to go on back up to the surface.
Off the island of Guam, the Trieste surfaces after a descent into the Mariana's Trench, the deepest. After nine grueling hours underwater, Walsh and Peicard returned to the surface on January 23rd, 1960, and officially entered the record books for the deepest dive of all time. To this day, their extraordinary feat has never been repeated.
