Why The Mariana Trench is Far More Dangerous Than Going to Space

Added: 2026-05-30

[00:00:00]Imagine you're inside a steel sphere the size of a phone booth, sinking through water so black that your flood lights illuminate nothing except the particles drifting upward past your viewport like snow falling in reverse. You've been falling for nearly 5 hours. The temperature outside the hull is barely above freezing and pressing against every square in of that steel with a patience that never waivers and a force that never forgives is roughly 16,000 lb of pressure. That's more than a thousand times the atmospheric pressure you're breathing right now. If the sphere cracked, if a single weld failed, if the metal gave way by even a fraction of an inch, the water wouldn't rush in. It would detonate inward at a speed your nervous system couldn't register. You wouldn't feel pain. You wouldn't feel anything. You would simply stop existing in a time frame measured in milliseconds. This is the Challenger Deep, the deepest known point on the surface of the Earth, nearly 7 mi straight down at the bottom of the Mariana Trench in the Western Pacific Ocean. And what I want you to understand over the course of this video is that reaching this place is more dangerous, more physically hostile, and more unforgiving than leaving the planet entirely.

[00:01:09]We have sent 12 people to walk on the surface of the moon. As of the latest count, roughly 27 people have ever reached the bottom of the Challenger Deep. And the overwhelming majority of those dives happened in just the last few years using a single submersible.

[00:01:23]For over half a century after the first dive in 1960, only two additional humans made the trip. The moon, a quarter of a million miles away, attracted more visitors than a trench sitting on our own ocean floor. There's a reason for that, and it starts with what 16,000 lb per square in actually means when it meets human tissue. Think about a single square in of your skin, the pad of your thumb, roughly. Now, imagine placing eight full-size pickup trucks on top of that thumbnail, stacking them, balancing all of their combined weight on a contact patch smaller than a postage stamp. That is the force the water exerts on every single square inch of everything at the bottom of the Mariana trend. Your entire body, if you were somehow exposed to that environment without protection, would be subjected to a compression so total and so instantaneous that the word crushing doesn't capture it. Crushing implies a process. This would be closer to a razor. Your lungs, which at sea level hold about 6 L of air, would collapse to a volume smaller than a pair of golf balls. The air pockets in your sinuses, the tiny gas- fil spaces in your inner ears, the dissolved gases in your bloodstream, all of it would be driven inward with catastrophic force. Nitrogen would be rammed into your tissues so fast that the normal process of narcosis, the slow, dreamy intoxication divers experience at moderate depths, wouldn't even have time to begin.

[00:02:42]Instead, the gas would simply obliterate cellular membranes on contact. Bones, which we think of as solid, are actually porous. They contain marrow. They contain air spaces. They contain fluid-filled canals. Under 16,000 PSI, those internal structures would implode.

[00:02:58]The skeleton wouldn't shatter the way a bone breaks from a fall. It would compress, fold inward, lose its architecture entirely. Every cavity in the human body, every pocket of gas, every hollow organ would be flattened in the same instant. The soft tissues, the muscles, the fat, the skin, they're mostly water, so they'd survive the pressure itself. But the structural damage from every air containing space collapsing simultaneously would be so violent and so complete that what remained wouldn't resemble a human body in any meaningful sense. This isn't speculation. This is fluid dynamics applied to anatomy. At depth, pressure doesn't discriminate. It finds every void, every bubble, every imperfection, and it eliminates them. And here's what makes the deep ocean particularly cruel compared to other hostile environments.

[00:03:42]The pressure increases continuously.

[00:03:44]There's no threshold you cross where things suddenly get dangerous. For every 33 ft you descend, another full atmosphere of pressure is added. At 300 ft, recreational divers are already at serious risk of nitrogen narcosis and oxygen toxicity. At 1,000 ft, the pressure is roughly 30 times what you'd feel at the surface. And only a handful of specialized military and commercial divers have ever worked at that depth using exotic gas mixtures and decompression schedules that can take days. The deepest any human has ever gone without a submersible breathing gas from the surface through a pressurized suit system is somewhere around 2,000 ft. The Challenger Deep is nearly 36,000 ft. 18 times deeper than the absolute limit of human dive physiology. The gap between what the human body can endure and what the trench demands isn't a gap at all. It's an abyss within the abyss.

[00:04:36]On January 23rd, 1960, two men climbed into a vessel called the Triest and dropped into the Mariana Trench. Jacques Picard, a Swiss engineer whose father had designed the craft, and Don Walsh, a lieutenant in the United States Navy.

[00:04:50]The Trieste was a ba'isgaff, a deep diving vessel that used gasoline for buoyancy and iron shot for ballast.

[00:04:56]Suspended beneath a float the size of a small submarine. The crew sphere where Pickard and Walsh sat shouldertosh shoulder was a forged steel ball less than 7 ft across with walls 5 in thick.

[00:05:08]Manufactured by the Crup Iron Works in Germany, they descended for 4 hours and 47 minutes. Nearly 5 hours of sinking through absolute darkness, watching their depth gauges climb past numbers that no human being had ever seen from the inside of a vessel. And then at roughly 30,000 ft, something happened that nearly ended the mission. A sharp, loud crack echoed through the sphere.

[00:05:30]The outer plexiglass window of the entrance tunnel had fractured under the thermal stress of the descent. The entire vessel shook. For a moment, neither man knew whether the pressure hull itself had been compromised. If it had, they would have been dead before the thought could finish forming. They checked the instruments. The sphere was holding. They made the decision to continue. When they finally touched bottom, their onboard systems read a depth of over 37,000 ft, though that number was later revised to approximately 10,916 m, roughly 35,800 ft. They stayed on the floor of the Challenger Deep for 20 minutes. 20 minutes at the deepest point on Earth, peering through a small viewport into a landscape of pale sediment that Peard described as a kind of datmacious ooze, the floor of the world, and it looked like wet talcum powder stretching into nothingness. Then they released their iron ballast and began the 3-hour ascent back to the surface. When they reached the top, they discovered the source of the crack. The plexiglass viewport in the entrance tube had fractured cleanly. If it had shattered fully and the tube had flooded, they would have been sealed inside their sphere with no way to exit, waiting to be towed back to port while trapped in a metal ball bobbing on the Pacific. The Triesta never dove to the Challenger Deep again, and no human being would return for 52 years. When James Cameron descended to the Challenger Deep on March 26th, 2012, he did it alone. His submersible, the Deep Sea Challenger, was a 24 foot vertical torpedo designed from scratch over seven years. Built in secret in Sydney, Australia, unlike the Trieste, which was a hulking vessel that weighed over 50,000 lb, the Deep Sea Challenger weighed about 12 tons and could descend at nearly 500 ft per minute, covering the full depth in roughly 2 and 1/2 hours. Cameron squeezed into a pilot sphere 43 in in diameter, barely wider than his shoulders. The hatch was 18 in across. Once it was bolted shut, he was sealed inside with six cameras, a bank of monitors, and a mechanical sampling arm. The sphere was so small that he could not fully extend his legs for the duration of the dive. He sat in a partial crouch for nearly 12 hours.

[00:07:30]During the descent, he passed the depth of the Titanic wreck in 35 minutes. He noted it like a mailbox at the end of a driveway. At roughly 15,000 ft, he passed the depth where a flood light bulb had imploded on a previous expedition he'd been part of, detonating with the force of a grenade just outside the hull of his submersible. He later said that if the deep sea challenger's hull failed at full depth, he wouldn't feel a thing. The implosion would be faster than his nervous system could process. When he reached the bottom, Cameron described the landscape as featureless and desolate gin clear water, a flat expanse of fine silt that rose in tendrils when disturbed, hanging in the water like cigarette smoke. He could see far into the distance with his flood lights, and there was nothing. No features, no relief, no sense of scale or direction, the most remote point on Earth, and it looked like an endless parking lot made of talcum powder.

[00:08:19]During his time on the bottom, systems began to fail. His thrusters malfunctioned. He lost the use of his hydraulic sampling arm. His ability to maneuver was severely compromised. He spent 3 hours on the seafloor, far less than the 6 hours he had planned, before deciding to abort and begin his ascent.

[00:08:35]The deep sea challenger was later donated to the Woods Hole Oceanographic Institution. Cameron has not returned to the Challenger Deep since. If you're finding this interesting, I'd appreciate it if you'd take a second to hit the like button and subscribe to the channel. It genuinely helps this content reach more people and allows me to keep making videos like this one. And if there's a topic you want me to cover, a specific wreck, a creature, a depth, an expedition, anything connected to the deep ocean, drop it in the comments. I read every single one. If you've got a correction or something to add to what I've covered, leave that, too. I take those seriously and I address them. Now, back to the trench. In April of 2019, a retired naval officer and private equity investor from Texas named Victor Visco climbed into a submersible called the limiting factor and set a new depth record. He reached 10,928 m, roughly 35,853 ft, 16 m deeper than any human had gone before. And then 2 days later, he did it again. The limiting factor was a different kind of machine from anything that had preceded it. Built by Triton submarines in Florida, it was designed from the beginning to be reusable, commercially certifiable, and capable of repeated full ocean depth dives. The Triesta dove to the Challenger Deep once. The Deep Sea Challenger dove once.

[00:09:51]The limiting factor dove four times in 8 days during that initial expedition alone. By 2022, Biscovo had personally made 15 descents to the Challenger Deep, 15 trips to the bottom of the world. The submersible was certified by DNVGL, a classification society that verifies the safety of maritime vessels, making it the first full ocean depth submersible to meet commercial safety standards. It could carry two people. Subsequent dives brought researchers, scientists, and eventually paying passengers to the bottom, including oceanographer Dawn Wright, who became the first person of African descent to visit the Challenger Deep, and Katherine Sullivan, a former astronaut who had already been to space and became the first woman to reach the deepest point in the ocean. When Vesco landed on his first dive, he looked out the viewport and saw something sitting on the sediment at 35,000 ft. A piece of plastic, a candy wrapper, or something resembling one resting on the floor of the most remote habitat on the planet. A 2019 study found microlastics in the gut of every single amphopod specimen collected from the Mariana Trench.

[00:10:55]Everyone at a depth where sunlight has never reached and no human civilization has ever existed, our waste arrived before we did. Now, here is where the comparison to space becomes difficult to ignore. In the vacuum of space, an unprotected human body does not explode.

[00:11:10]It does not instantly freeze. The Hollywood version is wrong. What actually happens, based on NASA and Air Force research conducted in the 1950s and 1960s using both animal subjects and accidental human exposures. Is this you lose consciousness in approximately 10 to 15 seconds. As the lack of external pressure causes rapid deoxxygenation of the blood, the moisture on your tongue and in your eyes begins to boil because the boiling point of water drops dramatically in a vacuum. Your skin swells as water vapor forms in the soft tissues beneath it, a process called ebism. But you remain alive and potentially recoverable, roughly 60 to 90 seconds. After that, the damage becomes irreversible. The heart stops.

[00:11:51]Circulation ceases. Death follows. In 1966, a NASA technician named Jim Leblanc was accidentally exposed to a near vacuum in a groundbased test chamber. He lost consciousness in about 14 seconds. He was recompressed and survived with no lasting effects. The human body, it turns out, can tolerate the vacuum of space for a brief window.

[00:12:11]The body has time, seconds, maybe a minute, in which rescue is theoretically possible. At the bottom of the Mariana Trench, there is no window. If a pressure hull fails at full depth, the inward rush of water at 16,000 lbs per square inch would compress the air inside the vessel so rapidly that it would reach temperatures exceeding 1,000° in a fraction of a millisecond.

[00:12:32]This is what happened to the Titan submersible in June 2023 at a depth of roughly 12,500 ft with pressure less than a quarter of what the Challenger Deep imposes. The five occupants were killed in an implosion that lasted approximately 1 millisecond. They experienced no pain. There was no moment of awareness. The physics of the event simply outpaced the speed of human perception. At Challenger Deep pressures, the same event would be even more violent, even more instantaneous, even more total. Space gives you a countdown. The deep ocean gives you nothing. Space is the absence of pressure. The deep ocean is the presence of all of it, stacked 7 mi high and pressing from every direction simultaneously. In space, your body slowly fails as gases expand and oxygen depletes. In the trench, your body would be compressed into a volume a fraction of its original size before a single nerve impulse could travel from your skin to your brain. You would be destroyed faster than you could be informed that you were in danger. There is no environment on Earth or off it that kills with less warning. And yet at the bottom of this place where pressure rules absolutely things are alive.