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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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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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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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이 영상으로 말하기 연습을 하는 이유는?
유튜브 영어 공부를 통해 자연스러운 영어 회화 연습을 하는 것은 매우 효과적입니다. 이 영상에서는 지구의 판 구조론에 관한 복잡한 개념을 다루고 있어, 과학적인 주제를 영어로 설명하는 연습에 안성맞춤입니다. 영어 회화 연습을 위해 이 영상을 활용하면, 어렵고 전문적인 어휘와 표현을 익힐 수 있으며, 지식을 쌓는 동시에 영어 실력을 향상시킬 수 있습니다. 또한, 다양한 억양과 발음을 접하면서 shadowspeak 기법으로 효과적으로 쉐도잉 연습을 할 수 있습니다.
문맥 속의 문법 및 표현
- Without plate tectonics, Earth would look very different - 이 표현은 가정법을 사용하여 조건적 상황을 설명합니다. 대화에서 가정법을 활용하면 원인과 결과를 더 명확히 전달할 수 있습니다.
- The idea that Earth's surface is made of rocky plates moving over a molten mantle - 이 구조는 복잡한 정보를 설명할 때 매우 유용합니다. that 절을 통해 구체적인 내용을 추가하여 문장을 풍부하게 만드는 연습을 할 수 있습니다.
- Scientists have been trying to solve the mystery - 현재완료 진행형을 사용하여 과거와 현재의 연속성을 강조합니다. 이는 연구나 발견과 같은 주제를 논의할 때 자주 사용되는 구조입니다.
자주하는 발음 함정
영상에서 몇 가지 발음 함정이 나타납니다. 예를 들어, tectonics, mantle, subduction와 같은 과학 용어는 발음이 어렵기 때문에 특히 주의가 필요합니다. 이 단어들을 반복 연습하면서 올바른 억양을 익혀보세요. 또한, ice sheets와 같은 구문에서는 발음할 때 음절을 명확히 구분하는 것이 중요합니다. shadowspeaks 기법을 활용하면 발음에 관한 짚고 넘어갈 부분을 쉽게 개선할 수 있습니다.
쉐도잉이란? 영어 실력을 빠르게 키우는 과학적 방법
쉐도잉(Shadowing)은 원래 전문 통역사 훈련을 위해 개발된 언어 학습 기법으로, 다언어 학자인 Dr. Alexander Arguelles에 의해 대중화된 방법입니다. 핵심 원리는 간단하지만 매우 강력합니다: 원어민의 영어를 들으면서 1~2초의 짧은 지연으로 즉시 소리 내어 따라 말하는 것——마치 '그림자(shadow)'처럼 화자를 따라가는 것입니다. 문법 공부나 수동적인 청취와 달리, 쉐도잉은 뇌와 입 근육이 동시에 실시간으로 영어를 처리하고 재현하도록 훈련합니다. 연구에 따르면 이 방법은 발음 정확도, 억양, 리듬, 연음, 청취력, 말하기 유창성을 크게 향상시킵니다. IELTS 스피킹 준비와 자연스러운 영어 소통을 원하는 분들에게 특히 효과적입니다.
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