00:00Our planet has five oceans.
00:02The Pacific, Atlantic, Indian, Southern, and Arctic.
00:06Not counting Billy Ocean.
00:09But it seems there's a sixth one out there too.
00:11It's just that you can't see it.
00:14Scientists have found evidence of large amounts of water hidden in the transition zone.
00:19That's the boundary layer that separates the upper and lower mantle of our planet.
00:23That boundary goes hundreds of miles deep down below the surface.
00:28Natural diamonds usually form in the mantle, but at depths of up to 155 miles.
00:34Some of them are very rare.
00:36They may come from deeper depths.
00:38That was the case with this fascinating diamond that formed 410 miles below the surface.
00:44The gem was big enough for scientists to study it and determine what it was made of.
00:48They were surprised when the composition of this very rare diamond
00:52showed that it was formed in pretty watery conditions.
00:56Because of that, such a diamond wouldn't be worth much in jewelry stores.
01:00But it was priceless in the lab.
01:03So, could this mean there's an ocean under the surface of our planet?
01:07It would definitely get us closer to the idea Jules Verne had about this whole magical secret world inside Earth.
01:15Including the ocean.
01:16But that's not exactly the case.
01:18The water is there, true.
01:21But it's not like you can enjoy the view watching waves splashing around like on the surface of our planet.
01:27The water is actually stored within the minerals.
01:30That's why this area is so wet.
01:33Let's now move to Africa to keep up with the story.
01:35Or, to be more specific, to a spot called the Afar region.
01:40It's part of Ethiopia and a place where three tectonic plates meet.
01:44Tectonic plates are large pieces of our planet's crust that slowly move.
01:50These movements cause earthquakes and produce volcanoes, mountains, deep underwater valleys we call trenches, and so on.
01:57And the Afar Valley is where the Arabian, Somali, and Nubian plates meet.
02:03Together, they form an intersection in the shape of a Y.
02:06Why? Let me tell you.
02:08These plates are moving all the time.
02:12The Somali plate is moving southeast toward the Australian and Indian plates.
02:16The Arabian plate is moving north, getting closer to the Eurasian plate.
02:21At some point, it will close the Persian Gulf.
02:24This movement of plates has created something we call the Great Rift Valley.
02:29Considering there are, you know, all these cool rifts.
02:32The Aden Ridge to the east, the Red Sea Rift to the west, the Oculus Rift, and the East African Rift to the south.
02:40But the East African Rift is something we want to focus on, because this one could be the key to this potential sixth ocean.
02:48But this time, on the surface.
02:50A continental rift is a spot where two tectonic plates that form a single continent start to separate.
02:57Here, it's the Somali and Nubian plates.
03:00Together, they're parts that make up Africa.
03:03If they keep moving in separate directions, this currently continental rift may become what we call an oceanic spreading ridge.
03:11In other words, when the plates are far enough apart from each other, there will be an enormous crack between them.
03:18This way, magma will freely flow up from beneath them.
03:22It'll be cool and eventually start creating a new ocean floor.
03:25Africa will be split into two parts, and there will be a new ocean flowing between what will turn into two mini-continents.
03:34Nope, it's not time to get your swim trunks and sunscreen yet.
03:38Even if the Somali and Arabian plates do move far enough to form an oceanic spreading ridge,
03:44it'll take, eh, millions of years before this happens.
03:47So I guess it's more interesting to stick to exploring this sixth ocean below the Earth's surface for now.
03:53The idea of subsurface oceans goes beyond the borders of our planet.
03:59It's possible many moons and planets out there have them too.
04:03Our home planet is the only one we know about with consistent bodies of liquid water on the surface, true.
04:09In our solar system, we circle around the Sun in something called the habitable zone.
04:15The temperature and atmospheric pressure within this zone allow water to remain in liquid form all the time.
04:22But a couple of moons in our solar system could also contain significant amounts of water under their surface.
04:30Enceladus, one of Saturn's moons, is the first one.
04:33Enceladus is a small frozen ball, seven times smaller in diameter than our moon.
04:39But it's the sixth biggest moon of Saturn.
04:42Nearly a decade ago, a spacecraft found evidence that there was a large ocean under its surface.
04:49It found and sampled water from the eruptions that resembled geysers.
04:53A geyser is a rare type of hot spring that erupts and sends jets of steam and water into the air.
04:59You know, like Old Faithful in Yellowstone?
05:02Well, this water was erupting through fissures in the ice at the south pole of the Moon.
05:07That means there might be a liquid ocean under the thick layers of ice.
05:12The ocean there is almost nothing like ours.
05:15The ocean on Earth is relatively shallow, on average 2.2 miles deep.
05:20And it covers three-quarters of our planet's surface.
05:23It gets colder the closer you come to the seafloor,
05:26and is warmer if you stay close to the surface because of the Sun's rays.
05:30But the subsurface ocean on Enceladus is at least 18 miles deep.
05:37It's cooler at the top because that part is near the ice shell,
05:41and warmer at the bottom because of the heat coming from the Moon's core.
05:45But both our ocean and the ocean on Enceladus are salty.
05:50Enceladus is one of the few places in our solar system that has liquid water,
05:54which makes it an interesting spot to search for signs of life.
05:59Another one is Europa, one of Jupiter's moons.
06:02Scientists think similar eruptions of water could be happening there.
06:07Knowing there are such geysers there tells us these moons have their own source of energy.
06:12Maybe the energy that makes the water erupt comes from gravity or radiation.
06:17The same energy could keep a large body of liquid water under the ice.
06:22It could even support some forms of life.
06:25There are thousands of planets beyond our solar system that orbit other stars.
06:30Some are even in the habitable zone.
06:33Over a quarter of the ones that we know about could have liquid water.
06:37But the majority of them probably have oceans under their surface,
06:41like Enceladus and Europa.
06:43Pluto might be on this list too, since it's possible it hides a liquid ocean under its thick frozen shell.
06:51This subsurface ocean likely formed long after the dwarf planet did,
06:55after the heat coming from radioactive elements in Pluto's core melted some of its ice.
07:01There's also something called water worlds.
07:04Those are moons or planets with global oceans that are more common than we thought.
07:09I mean, some call Earth a water world too.
07:1271% of its surface is water, after all.
07:16And when you look at our home planet from space, you mostly get those blue marble pictures.
07:22When exploring other planets, especially those outside of our solar system,
07:27researchers often go with a policy of follow the water.
07:31After all, water is the main element we know that's necessary for supporting life.
07:36And when there's a water world that's close to its parent star,
07:40scientists assume it must have formed way farther and then moved closer once its orbit shrank.
07:47The composition of the planet was set when it was in a colder orbit,
07:51or, in other words, when it made a wider circle around its star.
07:55We call the process of orbital shrinking a migration.
07:58And if water worlds are really that common, it can be proof that migration really happens.
08:06Exoplanets are all those planets that orbit around other stars, not our sun.
08:11Some exoplanets may have oceans that are way deeper than any of those in our solar system.
08:16Hundreds or even thousands of miles deep.
08:19Our Mariana Trench is scary, and it's not even 7 miles deep.
08:24And those exoplanet oceans are, wow, almost bottomless.
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