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Deep Sea Mysteries That Science Can't Explain! | Dhruv Rathee — Transcript

by Dhruv Rathee · 4,518 words · 515 segments · language en · Watch on YouTube

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0:0017th February 1977, near Ecuador, about 330 km from Galapagos Island,
0:06a small white submarine goes into the middle of the Pacific Ocean.
0:11It was called Alvin and it carried three men. One pilot and two scientists.
0:16Actually, they were geologists looking for sources of hot water in the ocean,
0:21the hydrothermal vents.
0:23But none of them were deep sea biologist,
0:25because back then, people believed that there was no life below the sea.
0:32About 2 days ago, these scientists dropped a 2 ton steel cage Angus into the sea,
0:38it had cameras and powerful lights.
0:41About 2.5 km below, where not even sunlight reaches,
0:45the lights on Angus turn on.
0:47Its sensors register the temperature of hot water and the scientists found their
0:57first hydrothermal vent.
1:00But when the three scientists sitting in this
1:02submarine go near the hydrothermal vent and
1:04look out of the window, they see something else.
1:09Something that shouldn't have been there.
1:13They see white clams of about 1 foot each on the rocks 50 metres away.
1:20These white insects with red caps are growing from the ground.
1:23They realize in a few minutes that this was not a barren place.
1:27Here was a whole city of sea animals.
1:31They could not understand how this could be possible.
1:45At that time, the most basic rule of biology
1:48was that every food chain on the earth starts
1:51with the sun.
1:52Plants make food using sunlight through photosynthesis.
1:56Animals eat plants.
1:57Without sun, there'd be no food.
1:58And without food, life couldn't exist.
2:01But that day, those scientists saw for themselves that life doesn't need the sun.
2:07They opened a door to a world that is on our own earth.
2:11But it looks like the alien world of some other planet.
2:16I'm talking about the deep sea.
2:18And today, after almost 50 years, I'm also going on a deep sea expedition.
2:22I want to take you on a ship 250 km from the coast of Norway.
2:27It carries a submarine that is headed to the deep sea.
2:35I want to introduce you to the scientists and biologists on this ship.
2:39So that you can know the secrets hidden in the depths of the sea.
2:47When we talk about the deep sea, we are talking about the part of the sea
2:51which is more than 200 metres below.
2:54So deep that even sunlight starts to disappear there.
2:58And after about 1,000 metres, or 1 kilometre, it becomes completely dark.
3:03Sunlight cannot reach there at all.
3:05And this is not a small part of the habitat volume of the earth,
3:09that is, the area where life exists,
3:12deep sea makes up 98.5% of it.
3:15In simple terms, it is the largest ecosystem of the earth.
3:19But despite this, by April 2026, only on 28% of the world's
3:24ocean floor has been mapped as per modern standards.
3:27More than 70% of it hasn't even been mapped properly yet.
3:32That means we don't what lies there exactly.
3:38We have much more detailed maps of the surface
3:41of the Moon and Mars than the sea floor.
3:43Think about it, not even light can reach, let alone humans,
3:47it seems impossible to imagine life there.
3:52Because there are three basic problems of having viable life in the deep sea.
3:56Pressure, darkness, and hunger.
3:59First of all, let's understand the pressure.
4:01The deeper we go, the higher the pressure.
4:05The Challenger Deep of the Mariana Trench is the deepest part of the earth.
4:09It is about 10,900 metres deep.
4:13If you lift Mount Everest and put it upside down,
4:16there'd be about 2 kilometres between the peak and the seafloor.
4:20Now, at this point, there's so much pressure that every
4:23square inch is weighed down by about 16,000 pounds.
4:27This is same as having 100 elephants stand on your head.
4:33As you can imagine, no thing can survive this much pressure.
4:37It will be crushed completely.
4:39Now, the question arises, how can animals living in
4:41the deep sea not be crushed under this much pressure?
4:43Actually, pressure crushes something only when it has air, gas, or some empty space.
4:50For example, our lungs, ears, and sinus are filled with air.
4:55So pressure can crush them.
4:57But deep sea creatures are almost entirely made up of water.
5:00And water doesn't compress.
5:03These deep sea animals have neither lungs nor swim bladders.
5:06So there is nothing to crush.
5:08So now the question arises on the other two problems.
5:10Darkness and hunger.
5:12To understand this, let's get back to the story from the beginning of this video.
5:16Hydro-thermal vents.
5:18Two years after the discovery of the hydrothermal vents in 1977,
5:21scientists returned to the same place in 1979.
5:24But this time they brought biologists with them.
5:28"Equipped with a revolutionary television camera,
5:31they will take unprecedented motion pictures
5:33of strange creatures in the black abyss."
5:36And the discovery they made here, changes the whole understanding of life.
5:41These scientists found giant tube worms here.
5:44They can be up to 2 metres long.
5:48They don't have a mouth to eat with or a digestive system to process food.
5:54So how do these tube worms survive without food?
5:58Scientists found that there is an organ in these
6:01worms, a Trophosome, which is full of bacteria.
6:04These worms absorb hydrogen sulphide from the oxygen
6:07and the fluids relesed by the hydrothermal vents.
6:11Hydrogen sulphide is poisonous for most
6:13animals, but it is the food of these tube worms.
6:17They transmit sulphide to bacteria through their blood.
6:20And the bacteria generate energy from it.
6:22And this energy is the food for the worms.
6:25This process is called Chemosynthesis.
6:28This process does not need the sun at all.
6:32This system works so well that these tube worms grow up to 80 cm in a year.
6:38The fastest growth rate of any marine invertebrate.
6:42But now the question arises that not every animal lives near hydrothermal vents.
6:47So not everyone can fulfil their need for food with sulphide.
6:50What do the other deep sea creatures do?
6:52The answer to this is marine snow.
6:55That is, dead microorganisms, fish waste,
6:58pieces of other animals and other things
7:00that fall slowly like snow from the surface of the sea to the bottom.
7:05But this isn't a lot of food
7:07because most of the marine snow is lost on the way.
7:10Only 0.5% to 2% of the surface food can reach the deep sea floor.
7:17That means the deep sea sees the most food scarcity on earth.
7:23And this hunger does two very strange things with animals.
7:27The first thing is Deep Sea Gigantism.
7:29Allowing them to grow to extraordinary sizes.
7:34Look at this insect.
7:35This is the best example of it.
7:37This is the Giant Isopod.
7:39it can be up to 20 inches long.
7:41As big as a cat.
7:44The other consequence of this hunger is that it slows them down.
7:48So slow that our brain can't process it.
7:51Let's understand this with an example.
7:53In 2007, a Giant Isopod was caught in Mexico
7:56and it was kept in Japan's Toba Aquarium.
8:00In the beginning, it was eating normally but on 2nd January
8:042009, it ate a small piece of a fish and then stopped eating.
8:09They tried every way to feed him.
8:11Fresh fish, different kinds of food,
8:14but the isopod did not even look at the food.
8:17One, two, and eventually five years passed.
8:21But the isopod did not eat.
8:30But even though it wasn't eating, it was alive and well.
8:33It went around the aquarium.
8:34People went there to see it and it became a celebrity in Japan.
8:38Finally, on 14th February 2014, it died.
8:41By then, it had gone 1,868 days without eating.
8:46When it was dissected after it died, the biologists
8:48couldn't find any obvious reason for it giving up food.
8:51We still don't know why it stopped eating all of a sudden.
8:55Some people believe that it happened because it was kept imprisoned.
8:59But the most remarkable part of this story is not that it gave up food.
9:03The real question is, how did it survive for so long without eating anything?
9:10Later in this video, I will show you the real specimens of such deep sea creatures.
9:15We will talk to some scientists studying the deep
9:18sea creatures to find out more about such questions.
9:21But do you know what, I do not have a background in marine biology.
9:25I have studied engineering.
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10:35In the deep sea, food doesn't arrive on a timetable.
10:40Sometimes the carcass of a dead fish, squid, or whale reaches down there.
10:44It's an influx of food.
10:45But no one knows when they'd get their next meal.
10:49That's why the Giant Isopods' biology is built around a feast and famine world.
10:54That is, eat a lot when you get a chance.
10:55Store it in your body and then reduce the energy expenditure to a great extent.
10:59So that you can live without eating for a long time.
11:02Now we have scientific evidence of this.
11:04In a research published in 2026, scientists found that the
11:08giant stomach of these Isopods can work like a food warehouse.
11:13Their metabolism is very low and in cold conditions, their energy
11:17control system helps them endure lack of food for a long time.
11:21This research doesn't tell us why that specific Isopod gave up eating.
11:24But it does explain that a Giant Isopod can survive without food for years.
11:36It may seem like a strange behaviour, but it's not strange in the deep sea.
11:40The story flips when a large creature like a whale dies.
11:44For deep sea creatures, this is no less than winning a lottery.
11:48The amount of food provided by a whale's carcass, is more than
11:50what can be delivered by marine snow over thousands of years.
11:53Think about it, thousands of years worth of food reaches them all of a sudden.
11:57Once the carcass reaches the sea floor, first,
11:59scavengers like hagfish and deep sea sharks have a feast.
12:03It takes them years or sometimes only a few months,
12:05to clean up all the soft tissue.
12:07Then the bacteria get their turn,
12:09they help decompose the whale's bones and release sulphide.
12:11The same element released by the hydrothermal vents.
12:13This creates a mini-ecosystem similar to that around hydrothermal vents.
12:18Just like the animals gather around hydrothermal vents,
12:21the sulphide released by the bones
12:23invite more such creatures to feed.
12:26According to a study from 2022,
12:28a whale's body can run this ecosystem for 100 years.
12:32And this is not a theory, we have evidence of this.
12:35In 2002, scientists found a whale skeleton in the Monterey Canyon.
12:39Insects were growing on it.
12:41Insects that hadn't been seen before.
12:44They were named Osedax, meaning 'bone-eating.'
12:48Osedax are a kind of bone worms,
12:50somewhat similar to the tube worms found near hydrothermal vents.
12:55They don't have a mouth or a stomach.
12:57They form a root system inside the whale's bone,
13:00and then with the help of symbiotic bacteria,
13:03they use the fats and oils in the bone as food.
13:07But the real twist is that in the beginning,
13:09scientists found only female bone worms.
13:11Not a single male.
13:12Where were all the males?
13:13The answer is, nowhere.
13:15When the scientists looked inside,
13:17they found that male bone worms live inside females.
13:21They are much smaller than females.
13:23Almost microscopic in size.
13:24They don't eat the bones.
13:26Neither do they grow.
13:27They are there for only one reason.
13:29Releasing sperm for reproduction.
13:32A female bone-worm can host more than 600 males.
13:35That is, one female can have more than 600 male companions.
13:38If you think that the definition of reproduction in the deep sea is different,
13:42then you are right.
13:44And the biggest example of this is the Anglerfish,
13:46the most famous face of the deep sea.
13:48You must have seen it in the film, Finding Nemo.
13:50It has terrifying teeth,
13:52and there is a shiny bulb on its head.
13:56This glowing part is called Esca.
13:58It contains a glowing bacteria called Photo-bacterium.
14:01This makes it glow in the dark.
14:04The Anglerfish house and feed the bacteria and get light in return.
14:08It's not just a moving lamp.
14:10It helps attract the prey in the dark.
14:14But the shocking thing is that male anglerfish don't have Esca.
14:18They don't shine.
14:20So what does a male anglerfish do?
14:22They only have one target.
14:23To find a female anglerfish in the thousands
14:26of kilometres wide, entirely dark, deep sea.
14:30Statistically, it is almost impossible to do so in such vast ocean.
14:35But evolution has found the solution to this nearly impossible problem,
14:39it is probably the most bizarre thing in biology.
14:42When a male anglerfish finds a female,
14:45it burrows its teeth in it and never lets go.
14:48These small male anglerfish
14:50fuse themselves completely in females many times larger than themselves.
14:54So much so that even their blood circulation even unites.
14:57"The bottom here is the male. He's attached himself and his mouth parts
15:00have receded and merged into her and her blood systems are now fused."
15:03It gets food, nutrition, and everything it might need from the female anglerfish.
15:07Since they don't need to see any longer, it loses its ability to see.
15:13In return, the male merely provides the female anglerfish sperm for reproduction.
15:18This kind of fusion between two bodies is not found anywhere else in nature.
15:23But the most interesting thing is that it
15:25should not be possible according to science.
15:28Vertebrates have a 500 million years old adaptive immune system,
15:31that attacks all external element that enters the body to protect it.
15:36This immune system causes rejection of transplanted organs in humans.
15:40But the female anglerfish's immune system does not reject the male anglerfish.
15:45This is quite amazing in itself.
15:48But there is another creature in the deep sea
15:50that sacrifices even more for its offsprings.
15:53In April 2007, a submarine went into the water.
15:57About 1,400 metres below sea level, a rock was
16:00being examined when an octopus was spotted.
16:05The team went back to that place 38 days later, only to
16:08find the same octopus on the same rock, stuck to their eggs.
16:13Over the next 4.5 years, scientists returned to the same place 18 times.
16:17And every time they found the octopus on the same rock, on top of their eggs.
16:22Scientists did not see it eat even once.
16:25Slowly its skin lost colour, its eyes became
16:29dull, but still for 53 months it remained there.
16:34It did not move.
16:35This was the longest egg brooding period of any animal.
16:38In October 2011, when scientists returned, the
16:41eggs had finally hatched and the octopus had left.
16:45Think about it, for 4 years, an octopus remained on the rock without feeding.
16:50All because everything slows down in the cold water.
16:54Its eggs needed time to mature.
17:00And this isn't just about the octopus.
17:02Everything slows down in the deep sea.
17:04Time moves differently down there.
17:06And the biggest proof of this is the Greenland Shark.
17:11It is a slow, almost blind shark living in the cold and
17:14deep waters of the Northern Atlantic and Arctic regions.
17:17It is so slow that it swims at the speed of a crawling baby.
17:21That is, even slower than a normal person's walking speed.
17:24Until 2016, there was very little information about it.
17:27We didn't know how long it lived.
17:30But then marine biologist Julius Nielsen tried a strange method.
17:34Actually, the middle part of the shark's eyes'
17:36lens is developed during birth and never changes.
17:39So he took out the lens from the eyes of 28 female
17:42sharks and put them through radiocarbon dating.
17:45It was found that the largest Greenland shark was 392 years old.
17:50Almost 400 years old.
17:52With a range of +/- 120 years.
17:54That means, the Greenland shark can possibly live up to 500 years.
17:59What is even more shocking is that this shark reaches its mature adult state
18:03when it's 150 years old.
18:05That means, while humans take 18 years to reach this stage,
18:09it takes this shark 150 years.
18:11Imagine, the oldest Greenland shark in the ocean today
18:14was probably born when Aurangzeb ruled over India.
18:17She became old enough to have a child, around the revolution of 1857.
18:25Everything that we have seen in this video so far,
18:27tube worms, osedax, anglerfish, octopus, and this shark,
18:31we know all of this because someone went down and found them.
18:36Scientists went down there and actually saw them.
18:40But the question is, how much have we seen?
18:43In May 2025, a study was published in the Science Advances Journal.
18:47In it, records of 43,681 deep sea dives from 1958 to present were collected.
18:54Every submarine, every ROV, every camera record was included in it.
18:58It a bid to calculate how much of the deep sea floor has been explored by humans.
19:04The answer was only 0.001%.
19:08Even less than this.
19:09That's why scientists are trying their best to
19:11understand this deep sea as much as possible.
19:14Some scientists have collaborated with
19:16Greenpeace for the Deep Sea Arctic Expedition.
19:20Two years ago, in 2024, the Norwegian government opened
19:24up a large part of its Arctic waters for deep sea mining.
19:28People protested against it.
19:30I made a video on it and hundreds of thousands of you had signed this petition.
19:35The result of all this effort and protest was that the
19:38Norwegian government has stopped this plan till at least 2029.
19:42This is good news but the most shocking thing
19:44here is that the area that was opened for mining,
19:47hadn't even been properly observed by humans.
19:50Scientists hadn't studied it.
19:52So to spread awareness about this and to increase scientific understanding,
19:56Greenpeace went on a deep sea mission with a
19:59team of top scientists from all over the world.
20:03And this team included top researchers from
20:05countries like Sweden, Spain, Norway and Germany.
20:09And here, they also invited me.
20:11To present these discoveries to the world.
20:14To you.
20:16So our original plan was to leave on the Greenpeace's ship, Witness.
20:20But unfortunately, Norwegian authorities didn't allow that.
20:25So we had to charter a boat and go to the sea.
20:28"It's 15 metres in there."
20:30So we just started sailing, as you can see in the background.
20:33And he told us that the water here is already 15 metres deep.
20:37Which is very deep.
20:39This is the captain of our boat.
20:43Who has taken over the command.
20:45The security procedures for these boats are quite heavy.
20:49As you can see, we have to wear such sturdy life jackets.
20:52It has hooks on it.
20:54We have to wear this overall.
21:00After a few hours of journey, we can see that big ship.
21:03The research vessel carrying the scientists.
21:09This is the ship.
21:16You can see 'Greenpeace Deep Arctic Expedition' written here.
21:26Then I entered this research vessel.
21:28It is very important to wear a helmet because of
21:30the heavy metal equipment lying around everywhere.
21:33You might hurt your head.
21:36And here you can see the robot which explores the depths of the ocean.
21:41They've named it Holly.
21:43Greenpeace has rented it for this entire expedition.
21:47So this is the robot that will work hard to go into the depths of the ocean.
21:52I would like to show the view from the front.
21:54This is the front of the robot and here you can see two hands, two robotic arms.
22:00There are clips at the end.
22:03They can extend these arms and grab samples from
22:06the depths of the ocean using these fingers.
22:09And this camera over here is extremely high-definition
22:13It will record everythinf it comes across at those depths.
22:18This is the room from where the deep-sea robot will be controlled
22:22Because it is a big robot it cannot be controlled by anyone alone.
22:25It needs 3 people.
22:27One person will sit here, one here, and one here.
22:29It can go down 3 km below the surface of water
22:35All the parts here are pressure tested.
22:42This machine over here is used to get this robot into the water.
22:51The people here won't say that they are 'driving' the robot.
22:57They'll say that they are flying it because it hovers a little above the sea bed,
23:03so that no organism gets hurt.
23:06I got the opportunity to talk to many scientists here
23:09and actually, the things they have discovered
23:12I got a chance to see it.
23:13Can I hold it?
23:15Yes, of course.
23:16With like this, right?
23:17Yeah.
23:18You can hold it.
23:23So, I have this deep sea starfish in my hands.
23:26Which can be touched.
23:27They told me it's not dangerous.
23:31The colour of it wasn't like that.
23:32It faded out when exposed to air.
23:34There's a whale bone here that they found in the deep sea.
23:38This one here.
23:41It looks like bread now.
23:43It does.
23:45That means the amphipods have been busy.
23:47They have been eating it all.
23:49They sink to the sea floor and when the whale
23:50gets eaten, that's the last piece of the marine.
23:53Dr. Paco Cardenas is a sponge scientist.
23:55Sponges are animals that look like this.
23:57And the sponges found in the deep sea,
24:01have some interesting things that are not found anywhere else.
24:05They are the only animals on our planet that have evolved a skeleton made of glass.
24:10Can I hold it?
24:12You can hold it but I will advise you to put some gloves because otherwise
24:17you will get some glass in your hands and that can be a little bit painful.
24:22We humans have to use high temperatures to make glass but these deep
24:27sea sponges naturally make that glass and that glass is present here.
24:33I am wearing gloves to hold this because it still has small spikes of glass on it.
24:38If I try to touch it normally, with naked fingers,
24:41the spikes of glass will get into my finger.
24:43And it will hurt a lot.
24:45And here under the microscope, are the creatures
24:49Crustaceans, which were actually present inside the sponges.
24:53They are being analysed here.
24:55And some creatures are like the aliens from the movie Alien.
25:00They look exactly like that.
25:02Very scary.
25:06In our body, bacteria are mostly limited to the intestines.
25:10And if they spread inside the body,
25:12we get sick.
25:13But in a sponge, bacteria don't just live inside them.
25:16But in between cells.
25:18And sometimes even inside the cells.
25:20And in some cases, they even live in the nucleus of the cells.
25:23But for sponges, the bacteria actually live inside of them.
25:27They live in total symbiosis.
25:30That means there is such a deep bond between the two,
25:33that without one, the other is incomplete.
25:35And this bond is no less than a superpower for scientists.
25:38Sponges continuously filter the ocean water.
25:41During this, small pieces of DNA of other living creatures that are floating around
25:46are also stored in them.
25:48That means one sponge alone becomes the natural DNA recorder of the entire area.
25:52So scientists can study the DNA evidence inside the sponge to find out
25:56which creatures lived around it.
25:58They have discovered such creatures, species,
26:01that no camera or submarine has ever seen.
26:04Perhaps to unlock the mystery of the deep sea,
26:07these sponges would play a major role.
26:10The deep sea into which the robot Holly went,
26:12that area is known as Loki's Castle.
26:16Below, the robot opened its arms and showed a banner,
26:20which read,
26:21Listen to the Science.
26:22This has become the deepest banner protest in the world.
26:26The data collected during this expedition,
26:28and the videos that the robot recorded for more than 100 hours,
26:31are with the scientists.
26:33This is the place where the footage is collected and stored in the computer
26:38they are reviews and the interesting parts are compiled.
26:42The videographers sitting here work very hard.
26:46They just watch the footage for hours and clip the interesting parts
26:50and make a compilation video of it.
26:54So the white thing is a squid.
26:56And the fish is taking a big bite.
26:59And wrestling it a little.
27:02Is this a jellyfish?
27:04It's a jellyfish.
27:06It looks like a spaceship.
27:08Yeah.
27:10So many shrimps.
27:12So much life in the water.
27:14Wow.
27:16That's incredible.
27:18Scientists will now analyse all this
27:20and in the coming months, we will see
27:22many new species.
27:24Many secrets will be revealed.
27:26Many new facts will be known.
27:28Greenpeace as an organization
27:30wants to use all this for two purposes.
27:32First, stop deep sea mining completely.
27:36Second, try to create protected areas in the sea.
27:40We often talk about saving those things that we see.
27:43Forests, rivers, animals.
27:45But there is a world that we have not seen properly till now.
27:49Will we save it or lose it without ever discovering?
27:53This question is not only for scientists, it is for all of us.
27:56The link to Greenpeace's petition to stop
27:57deep sea mining is in the description below.
28:00If you haven't signed it yet, then do it.
28:02This will not only pressure the Norwegian government,
28:04but also every government in the world.
28:07It will pressureise the United Nations.
28:09The more people sign it, the more pressure can be exerted
28:13to permanently ban deep sea mining.
28:16And the glimpse of the world you saw in this video,
28:19we will be able to save that world for the coming generations.
28:24Before you go, don't forget to join the YouTube Blueprint course.
28:27The coupon code is DEEPSEA40.
28:29And if you liked this video,
28:30then I went on another mission in Sri Lanka.
28:33Where we discovered a new species in the jungle
28:36with one of the top scientists of Sri Lanka.
28:39There we found an animal that will be named after me.
28:44To know the whole story, click here.
28:47Thank you very much.

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