00:01This whole part of our planet has disappeared.
00:04It used to be a tectonic plate, but something that big doesn't just vanish without a trace.
00:10And the clues that led to its discovery started in this mysterious gap between South China and the island called Borneo.
00:19For a long time, people thought the sea between these two places sat on a tectonic plate called Izanagi,
00:26which no longer exists. But wait, how does a tectonic plate just vanish like that?
00:33Alright, tectonic plates are like pieces of a puzzle all connected together.
00:38But instead of sitting on a table, they're floating on this semi-fluid layer.
00:43So, they're always shifting and bumping into each other. And there's something else.
00:48Some pieces of this puzzle are heavier than others.
00:52And what happens is that eventually, a heavier piece slips under a lighter one.
00:59Something similar happens with tectonic plates, but it's less about weight and more about density.
01:05When the edge of one plate sinks below another and gets pushed down into the mantle, that process is called subduction.
01:14But it's not just the edge that can sink. Entire massive plates from the past have completely vanished into the Earth's mantle.
01:23That's exactly what happened to the Izanagi plate.
01:26About 130 million years ago, it started sliding under the Okhotsk plate, getting swallowed little by little.
01:35By around 55 million years ago, it was completely subducted and replaced by the Pacific plate.
01:42And for years, specialists thought that the ocean between China and Borneo was sitting on that plate before it disappeared.
01:50Cool, but the experts got it wrong.
01:53Turns out, the ocean between these lands wasn't sitting on the Izanagi plate after all.
01:58Instead, it fits into this weird, unexplained gap, as if a piece of the puzzle was missing.
02:06Recently, researchers at Utrecht University finally discovered that this gap was actually a ghost tectonic plate that no one knew about.
02:16The Pontus plate. It got its name because back when it existed, it sat beneath the ancient Pontus Ocean.
02:25But if it vanished so long ago, how did experts find it, right?
02:29Luckily, tectonic plates sometimes leave traces before they completely disappear.
02:35But instead of investigating footprints or fingerprints, it's more about looking for rocks.
02:41Yeah, stones from a lost plate can get incorporated into mountain ranges and show us where those ancient Earth layers were.
02:50That's because rocks have a special power to record Earth's magnetic field.
02:55You know, that invisible shield that protects our planet from space threats like solar wind and cosmic rays?
03:02So, as rocks cool and solidify, the magnetic materials in them, like magnetite or hematite, line up with Earth's magnetic field at the time and get locked in.
03:14They can freeze a record of the magnetic field direction and strength.
03:19And since it changes depending on latitude, basically whether it's further north or south on the planet,
03:26it allows the rocks to kind of take a snapshot of their ancient position relative to the equator.
03:33Knowing this, researchers traveled to Borneo to collect and study the rocks over there.
03:39And they discovered something odd.
03:42These stones were originally from a much farther north region.
03:46Their ancient coordinates didn't match the latitude they expected for Izanagi.
03:51In fact, they didn't match any of the tectonic plates we knew about up until then.
03:57So they quickly realized two things.
04:00One, they had just discovered an eerie gap.
04:03Two, there must be a hidden ghost tectonic plate that used to be in that spot.
04:09To unravel the mystery, scientists used computer models to study the region's geology over the last 160 million years.
04:18Thanks to this technology, they were able to piece together the entire Pontus Plate in all its glory.
04:25The next step was to figure out the key features of this part of our planet that had been submerged, like its age.
04:33You see, the rock samples collected in Borneo date back 135 million years, back when dinosaurs ruled the Earth.
04:42With this information, scientists realized that the Pontus Plate was formed at least 160 million years ago.
04:49But it's probably even older than that.
04:52Although it is hard to pin down exactly when it was formed, one thing we can say for sure.
04:59It was huge.
05:00The Pontus Plate was about one-quarter the size of the Pacific Ocean.
05:05Unfortunately, by around 20 million years ago, it said bye-bye to the planet, sinking and being completely pushed under the Australian Plate to the south and China to the north.
05:17At this point, you might be wondering if a couple of rocks and a computer reconstruction are enough to prove that the Pontus Plate really existed.
05:26Well, yeah, they are.
05:28But other clues have also been found in Palawan, an island in the western Philippines and in the South China Sea.
05:35The truth is that the scientific community has suspected the existence of Pontus for over 10 years.
05:42At that time, researchers were really focused on the area around the Philippines.
05:47This region is like a playground for geologists, since it sits at the crossroads of several tectonic plate systems.
05:55So, scientists decided to reconstruct the movements of the Earth's crust between Japan and New Zealand.
06:02And because of that, the study suggested there had to be a subduction zone running through there, separating the known Pacific plates in the east from the hypothetical Pontus Plate in the west.
06:14These previous predictions were possible because tectonic plates are really bad at playing hide-and-seek.
06:23Like we said before, before they get submerged, they leave clues behind.
06:28And it's not just rocks.
06:30They can also change the Earth's mantle, which leads to the formation of volcanoes, earthquakes and deep ocean trenches, for example.
06:39But the subduction process can also mess with the composition and temperature of the mantle, making some areas hotter or cooler.
06:47These are considered anomalies.
06:50It is possible to detect these anomalies using seismographs, which are instruments that pick up earthquake signals and record the ground's motion.
06:59When earthquakes happen, they send out ripples or waves through the Earth.
07:04These waves travel through the Earth's layers.
07:07But if they hit something unusual, like an ancient piece of a tectonic plate hidden in the mantle, the waves get disrupted.
07:15It's like hitting a bump on a smooth road.
07:18It messes with the ride.
07:20Using regular seismometers to look for anomalies is fine, and it can totally help us find clues about the Earth's past.
07:27But if scientists want to use this method to get pictures of what's really going on beneath the surface, it gets a lot trickier.
07:35Not only do the images come out in low resolution, but the process also becomes insanely expensive.
07:42So recently, experts just uncovered a cutting edge technique that could completely change the way we look at the Earth's depths.
07:50Kind of like an ultrasound, scientists can now actually see what's happening miles beneath our feet.
07:58More specifically, in a region between the Earth's brittle crust and the mantle underneath, known as the MOHO.
08:05This new method is called Distributed Acoustic Sensing, or DAS .
08:12It uses fiber-optic cables, the same ones that give us high-speed internet as earthquake sensors.
08:19Here's how it works.
08:21Laser beams are sent through the cables, and when the ground moves, whether from an earthquake, traffic, or other vibrations,
08:29the shaking changes how the laser light bounces around inside the cables.
08:35The cool part is that we can now measure these changes all along the length of the cable,
08:40so the cable ends up acting like hundreds of tiny earthquake detectors spread out over a huge area.
08:47This new tech can tell us things like whether major faults go all the way into the mantle,
08:53how ancient and modern processes have shaped the continents, and how strong the deep crust is in certain areas.
09:01In other words, DAS could be a game-changing instrument to help us uncover new clues about hidden and ancient tectonic plates.
09:10That's it for today. So hey, if you pacified your curiosity, then give the video a like and share it with your friends.
09:16Or if you want more, just click on these videos and stay on the Bright Side!
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