Prática de Shadowing: The Graveyard at the Center of the Earth - Aprenda a falar inglês com o YouTube
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Without plate tectonics, the Earth would look very different than it does today.
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Without plate tectonics, the Earth would look very different than it does today.
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Our mountain ranges, oceans, volcanoes,
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and even entire continents all get their recognizable features from the shifting rock plates on the Earth's mantle.
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And those features are pretty good evidence that plate tectonics works.
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But knowing if something works doesn't always mean we know why or how it works.
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And when it comes to plate tectonics,
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continents move in complicated ways.
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Scientists have been trying to solve the mystery of why plate tectonics works the way it does for over a hundred years,
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and they might have just uncovered a key to cracking it.
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The answer may be buried in a bizarre mirror world deep inside the Earth,
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where movement beneath the surface looks a lot like it involves the remains of former crustal rocks.
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Places of crusts we thought disappeared hundreds of millions of years ago,
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but now live inside the planet,
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like a graveyard of ancient plates.
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When scientists first embraced plate tectonics around the 1960s,
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the theory explained many observations about the planet.
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The idea
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that Earth's surface is made of rocky plates moving over a
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molten mantle explains why large mountain ranges form in the middle of oceans, for example.
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as Earth's mantle is creating new plates.
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And why deep trenches form at the edges of the oceans,
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where one plate is diving beneath another.
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Tying together these observations, geologists realize that tectonics works as a system.
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Plates are created at mid-ocean ridges,
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then move away from them and finally disappear back into the Earth at subduction zones,
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creating most volcanoes and many large earthquakes in the process.
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But even though the theory that recognized the constant cycle by which landforms are created was a breakthrough,
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it didn't exactly explain how this happens.
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What force could move massive plates,
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which can weigh a made-up sounding 5 quintillion tons around like driftwood?
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Early in the days of plate tectonic theory,
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geologists and geophysicists assumed plates move because of mantle convection.
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Currents of hot, molten material rising inside the Earth push the plates,
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dragging them along the surface the way rising bubbles move foam in a pot of boiling water.
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Logically, that idea makes sense.
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But scientists quickly realized that the physics of mantle convection don't totally add up.
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Now, the mantle definitely does have currents.
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Since 1971, scientists have known that rising plumes of magma travel from deep inside the Earth to the surface,
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creating islands like Hawaii and Iceland.
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But around the same time,
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researchers also realized something about the mantle's makeup that complicates the effect those currents could possibly have.
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See, they were looking at how continents move during ice ages,
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when the weight of massive ice sheets pushed them down into the mantle.
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And how, when the ice later melted,
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the same continents began popping back up.
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So they used data from a satellite to measure the gradual upward movement of the continent relative to the ocean's surface,
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to see just how fast the now deglaciated continents were popping back up.
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And even though they couldn't see the mantle below the continents,
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knowing the rate at which the mantle pushed continents up let scientists calculate its viscosity,
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that is, how runny it is.
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They found that the Earth's mantle is much runnier than expected.
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Later researchers estimated that the mantle is about a billion times runnier than the lithosphere,
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or crust, that sits on top of it.
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So those mantle currents simply couldn't be enough to move the plates the way we know they move.
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There must have been another force helping propel this movement.
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Even more mysteriously, geophysicists modeling Earth's mantle and continents found the Earth should have what's called a stagnant lid,
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where the lithosphere sits in place on the surface as mantle currents move underneath.
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In fact, Earth is the only place we know,
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for sure, where continents move,
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crash into each other, rise, and fall.
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So why does Earth have such unique tectonics?
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It all comes back to the mantle,
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which, as scientists noted back in the 1960s,
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shapes an important feature of tectonic subduction.
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That's the process where plates slip underneath another,
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driving back towards the center of the planet.
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And while it's another process that we can't directly see,
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it's one scientists inferred must be taking place once they noted some odd features of earthquakes.
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With the installation of big seismograph networks,
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geophysicists could suddenly tell exactly where and how deep earthquakes happened.
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And when they looked at big tremors in places like Alaska,
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they saw earthquake epicenters were far below the crust.
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In fact, some earthquakes were happening hundreds of kilometers down inside the mantle.
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That suggests that the stress of the plate bending deep down is triggering these earthquakes.
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Researchers realized that these quakes were like a sonar scan,
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revealing locations of where plates were driving down into the mantle.
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They were seeing the edge of the subducting plate that had disappeared under another plate long ago.
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Earth is also the only planet we know where subduction connects the surface to the interior in a major way.
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And scientists soon figured out that subduction helps explain why tectonics works the way it does.
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Because as geologists reasoned, if plate edges sank into the mantle,
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they'd likely pull on the rest of the plate, dragging it along.
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Initially, this was purely logical speculation.
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Again, we can't see any of this.
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But when scientists plugged this new force,
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called slab-pull, into models, the calculations worked better than mantle convection alone.
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But even with extra force from slab-pull added into the equation,
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the models still didn't quite fit Earth's tectonics.
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Plates still moved faster than the models predicted.
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There must be other forces helping move the continents.
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So scientists kept digging.
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In the mid-1970s, they noted that mid-ocean ridges are usually topographic highs.
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So as new plate material moves away from the ridges,
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it travels downward, as if descending from a mountain.
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This is due to gravity pulling down,
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adding a little force in the process scientists call ridge push.
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And scientists found this does help move us closer than the two forces of convection and slab pull alone.
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But according to the models,
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the addition of ridge push still wasn't enough to explain how fast our continents move either.
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There had to be something else,
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at least one more factor.
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Scientists then turned to another possible force acting on continents in the 1980s,
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something they called slab suction.
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Slab suction happens when the mantle flows around a sinking plate edge,
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pulling it downward more than just gravity alone.
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Like in movies, where people swimming away from a sinking ship get sucked underwater as the boat disappears below the surface.
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So in the early 2000s,
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scientists added slab suction to their models,
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and found this matched observed plate movements a lot more than before.
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So now we have four forces helping move continents.
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Mantle convection, ridge push, slab pull from the weight of the plate sinking into the Earth,
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and slab suction pulling even harder as those plates get sucked into the lower mantle.
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Adding together all these forces,
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we get a better idea of why Earth's tectonics works.
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Plates are created at mid-ocean ridges,
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and get pushed away from those ridges by gravity and mantle currents.
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Eventually, plates dive back into the mantle,
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pulling the plates along, with suction then dragging them down even harder.
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But what makes those pieces subduct and sink back into the mantle?
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This isn't something we see happening on any other planets in our solar system.
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This is where the bizarre mirror world comes in.
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See, seismic studies done in the mid-2010s show two huge zones of something unusual at the base of the mantle,
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one below the Pacific Ocean and another underneath Africa.
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When seismic waves hit these zones,
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they slow down, unlike how they move through the rest of the mantle.
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Geophysicists call these massive 15,000-kilometer-wide features large, low-velocity provinces, or LLVPs.
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They can tell from the way LLVPs react seismically that they're probably denser than the surrounding mantle,
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and possibly made of different material.
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And the strangest thing is,
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these LLVPs seem to move around much the same way continents do on the Earth's surface.
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They collide, assemble, and possibly even break apart, just like continents.
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In fact, scientists recently uncovered evidence
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that some of them might actually contain the remains of continents that used to be on the Earth's surface.
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Continents we thought disappeared hundreds of millions of years ago.
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The geophysicists running the models to figure out what LLVPs might be made of found
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that they could be the remains of old surface plates that sunk towards the core of the Earth in a giant pile,
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like a graveyard.
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The idea of this slab graveyard could explain a few things we see at the surface.
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Like how erupting lavas in places like Hawaii are oddly enriched in the isotope helium-3.
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Or how volcanoes in both the South Pacific and off the West African coast erupt unusually high amounts of uranium.
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Those are both elements we'd expect to see on Earth's surface,
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rather than in plumes from the mantle.
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But helium and uranium makes more sense if remnants of Earth's surface,
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sunk deep into the mantle, are feeding plume eruptions.
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So those mirror slabs inside the lower mantle are probably,
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at least partly, the remains of old plates that got subducted and then sank.
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And there, invisible to us at the surface,
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it seems they continue to play a role in plate tectonics.
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Like, they probably determine mantle currents.
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When plotting major mantle plumes that have erupted onto Earth's surface,
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geologists notice that they all seem to burst forth from LLVP zones.
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And these could also be the reason we have subduction.
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Although most subduction zones lie well away from these deep earth structures,
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it might be the case that mantle currents rise above LLVPs,
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pushing plates off to the sides.
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Then once the plates are pushed away from the upwelling plumes above LLVPs,
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they start to sink, subducting.
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When researchers plug in all the data we have on the mantle and the movements of continents,
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that scenario is exactly what they see.
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And it all comes full circle when the sinking plates absorb back into the LLVP graveyard,
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deep in the mantle, and the cycle continues.
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Now, not all scientists agree with this theory.
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For example, there's debate about whether mantle plumes rise from the center of LLVPs or from their edges.
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Scientists also argue about whether LLVPs stay in one place or migrate around the mantle.
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Another hypothesis argues that LLVPs are actually the remnants of an ancient planet that crashed into early Earth,
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which we talk about in our episode When Earth Ate a Planet.
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Overall, LLVPs are pretty mysterious.
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Even after decades of research into plate tectonics,
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and a solid understanding of how it works,
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the question of why it works has been harder to pin down.
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But it appears that from deep in the Earth,
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this ancient mirror world has something to do with driving tectonics,
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the thing that makes our planet unique,
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as far as we know.
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And given that the mirror plates seem as active as the surface continents,
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the future of tectonics could be as surprising as this bizarre discovery itself.
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Eons is possible thanks to rad viewers like you,
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This art is also featured on our new Permian t-shirt, which absolutely rules!
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Many Eons viewers remember that for a good long time,
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our videos used to end with a shout out to one of our patrons, Steve.
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And to celebrate with the entire Eons community this Patron Appreciation Month,
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Thank you for all your support.
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So we're still figuring out the details of plate tectonics,
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but we can clearly see the effects on our modern world,
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if you know where to look.
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Join Michelle Barbosa-Ramirez and Blake DePastino on a field trip to explore the epic natural history saga of LA in our episode,
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How Plate Tectonics Transformed Los Angeles.
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We gotta thank this month's Tectonic Eontologists.
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Addie, Annie and Eric Higgins,
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Carl Wolfel, Jackie Scott Ralston,
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Jake Hart, John Davidson Ng,
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Juan M, Melanie Lam Carnivale,
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Nico Robin, and Raphael Hassa.
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Become an Eonite at patreon.com slash eons and you can get fun perks like access to a monthly digital paleo art puzzle.
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And as always, thank you for joining me in the Ken Barnes studio.
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Subscribe at youtube.com slash eons for more adventures and deep time.
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Continental Drift came out in 1912 and everybody was like,
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y'all crazy, y'all crazy.
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And then around the 1960s they were like,
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eh, maybe you're not as crazy as we thought you were.
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So it took like 50 years for scientists to be like,
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nah, this is real.
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This is, this is it.
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Por que praticar a fala com este vídeo?
Assistir e praticar a fala com "The Graveyard at the Center of the Earth" é uma excelente maneira de melhorar suas habilidades de conversação em inglês. O vídeo explora conceitos intrigantes sobre tectônica de placas com uma linguagem acessível e informativa. Ao praticar com este conteúdo, você não apenas absorve novo vocabulário e expressões, mas também se familiariza com o ritmo e a entonação do inglês falado. Isso o ajuda a desenvolver a fluência necessária para interagir em discussões sobre ciência e natureza, tópicos frequentemente abordados em contextos acadêmicos e informais. A prática de conversação em inglês com vídeos como este pode acelerar seu aprendizado, tornando-o mais autêntico e eficaz.
Gramática & Expressões em Contexto
O discurso deste vídeo apresenta várias estruturas gramaticais e expressões que são valiosas para o aprendizado da língua:
- Passive Voice: A frase "is made of rocky plates" exemplifica o uso da voz passiva, comum quando o foco está na ação, não no agente. Essa estrutura é útil para discussões científicas e acadêmicas.
- Present Continuous: A expressão "plates are created at mid-ocean ridges" ilustra como o tempo presente contínuo é utilizado para descrever ações em andamento, essencial para transmitir eventos atuais ou processos.
- Cause and Effect: Estruturas como "this explains why large mountain ranges form" ajudam a entender relações de causa e efeito, uma habilidade fundamental para debates e explicações claras em inglês.
Armadilhas Comuns de Pronúncia
Existem algumas palavras e trechos do vídeo que podem representar desafios na pronúncia. Preste atenção especial nas seguintes palavras:
- Tectonics: A pronúncia correta é crucial, pois é uma palavra frequentemente utilizada em contextos científicos. Pode ser difícil para falantes não nativos.
- Subduction: Essa palavra, que se referindo ao processo de uma placa tectônica sendo empurrada para baixo de outra, tem uma certa musicalidade que pode ser complicada para alguns alunos.
- Continents: O som da letra 'nt' no final pode ser difícil de pronunciar. Praticar a articulação clara é fundamental para evitar confusões.
Para melhorar sua pronúncia e fluência, recomenda-se a técnica de shadowing, onde você repete o que ouve no vídeo, sincronizando-se com a fala dos nativos. Essa abordagem não apenas aprimora a pronúncia, mas também ajuda a internalizar estruturas gramaticais e vocabulário. Utilize a prática de conversação em inglês em plataformas interativas ou grupos de estudo para ampliar suas oportunidades de aprendizado.
Invista em sua jornada de aprender inglês com YouTube através do shadowspeaks e observe como a prática contínua pode transformar sua capacidade de comunicação!
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.
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