シャドーイング練習: What Would Happen If an Asteroid Hit the Ocean? - 動画で英語スピーキングを学ぶ
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193 文
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70 % of this planet is water, which means that if something falls out of the sky and hits us,
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the odds are overwhelmingly that it lands in the ocean rather than on land.
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Most people find that reassuring.
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The ocean feels like a cushion.
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It is deep, it is empty, and there are no cities out there to destroy.
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If a mountain of rock is going to fall on the earth,
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surely the middle of the Pacific is the best possible place for it to land.
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That instinct is completely understandable, and it is wrong in a way that took scientists a surprisingly long time to work out.
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Because water does not absorb an impact like that.
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Water does something far worse.
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It takes the energy, holds onto it and then carries it thousands of kilometers to a coastline where people actually live.
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And that is only the first of the three separate disasters an ocean impact sets in motion.
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And it is not the one that kills the most people.
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By the end of this you will understand why the ocean is not a cushion at all.
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It is a delivery system.
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Before we drop anything, we have to be honest about scale.
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Because asteroid hits the ocean covers an enormous range of outcomes, from nothing at all to the end of civilization.
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Small objects hit our atmosphere constantly.
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Every single day, tons of material from space runs into the Earth, and almost all of it burns up long before it reaches the surface.
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Those are the shooting stars you see on a clear night, and they pose no threat to anyone.
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Push the scale up to a few meters across, and you get the events that occasionally make the news.
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An object explodes in the upper atmosphere, produces a spectacular fireball, rattles some windows,
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and scatters fragments across a landscape.
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Anything landing in the ocean at that size vanishes without a single person noticing.
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The situation changes at somewhere in the region of a hundred meters.
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An object that size carries enough energy to survive the atmosphere and deliver a serious impact.
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And if it lands in water, it starts generating waves that matter.
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At around a kilometer, you are looking at a genuine global threat, regardless of where it hits.
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And at 10 to 15 kilometers, which is roughly the size of the object that ended the dinosaurs, the location almost stops mattering.
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That is not a regional disaster, that is a planetary reset.
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For most of this video, we are going to focus on the range that is actually most likely to happen in a human lifetime,
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which is the few hundred meter object, because that is where the odds and the consequences intersect most uncomfortably.
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But we will come back to the big one, because the day the dinosaurs died was an ocean impact,
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and what happened next is genuinely difficult to imagine.
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Picture a rocky object 300 meters across on a collision course with the middle of an ocean.
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It is traveling somewhere in the region of 20 kilometers per second.
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The first thing to understand is that at that speed our atmosphere barely exists.
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A hundred kilometers of air, the thing that protects every living creature on this planet, is crossed in a handful of seconds.
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The object compresses the air in front of it so violently that the air itself glows white -hot,
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and anyone within sight of the sky sees a light brighter than the sun tearing across it.
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Then it reaches the water and here is where our intuition fails us completely.
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When you imagine something falling into the sea, you probably picture a splash.
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Something enters, water parts, water closes over it, ripples spread out.
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That image is based on a lifetime of watching objects drop into water at ordinary speeds.
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At 20 km per second, water does not behave like a liquid at all.
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It does not have time to flow out of the way.
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On the time scale of the impact,
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seawater behaves more like a solid and the collision is closer to rock striking rock than to a stone hitting a pond.
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The object does not sink.
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It is.. destroyed.
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It is annihilated on contact, converting an enormous quantity of kinetic energy into heat and pressure in an instant,
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and in the process it vaporizes a colossal volume of seawater around it.
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What opens up in the ocean at that moment is not a splash.
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It is a crater in the water itself, A transient cavity that can be several kilometers across and,
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in deeper water, may reach all the way to the sea floor.
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For a brief moment, there is a hole in the ocean with steam -filled walls, and you could look down through it and see the seabed.
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The ocean, of course, does not tolerate that for long.
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The cavity begins collapsing almost immediately, and this is the moment that creates the disaster.
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Billions of tons of seawater rush inward from every direction to fill the hole.
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And all of that water arrives at the center at the same time, with nowhere left to go but up.
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It rebounds, forming an enormous column of water that rises high into the atmosphere before falling back and collapsing again.
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near the impact point we are potentially talking about waves hundreds of meters high
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now this is the point where most explanations of ocean impacts go badly wrong
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and I want to correct it carefully because the correction is actually more interesting than the myth
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The common claim is that an ocean impact produces a wall of water hundreds of meters tall
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that sweeps across the entire ocean and washes over continents.
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That version is not what the physics predicts, and it is worth understanding exactly why.
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Impact waves and earthquake tsunamis are not the same animal.
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An earthquake tsunami is generated when a long section of the seafloor, sometimes hundreds of kilometers of it, shifts vertically all at once.
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That displaces an enormous volume of water along a very long front, and it produces a wave with a very long wavelength.
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Long wavelength waves are extraordinarily efficient at crossing oceans, losing very little energy on the way,
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which is why a quake off one coast can devastate a shoreline on the far side of the world many hours later.
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An impact wave is generated by a single point and the waves it produces have much shorter wavelengths.
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Short wavelength waves lose energy far more rapidly as they spread.
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The wavefront expands outward as a growing circle and the same energy is distributed across an ever larger circumference,
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so the height falls off quickly with distance.
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So the honest picture is this.
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Close to the impact, the waves are apocalyptic and nothing survives.
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At intermediate distances, they are still catastrophic, and by the time they reach a distant continent, they may be far smaller than the myth suggests,
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though still large enough to be a serious coastal disaster.
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That sounds like good news, and up to a point it is, but there is a detail hiding in that reassurance that turns it around completely,
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and it has to do with where we choose to live.
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Here is the uncomfortable arithmetic.
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Something in the region of 40 % of humanity lives within 100 kilometers of a coast.
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The great cities of the world are overwhelmingly coastal because for the whole of human history,
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access to the sea has meant access to trade, food and travel.
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We built our civilization at the water's edge on purpose.
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That means the specific weakness of an ocean impact, its ability to convert energy into moving water,
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is aimed directly at where we keep almost half our population and a large fraction of our infrastructure.
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And there is a second problem that makes the wave heights out in the open ocean misleading.
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When a wave moves into shallow water near a coastline, it slows down and the energy it carries has to go somewhere.
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It goes upward.
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The wave grows dramatically as it approaches the shore, a process called shoaling.
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A wave that seems modest in deep water can become something entirely different when it arrives at a continental shelf.
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Local geography then makes it worse or better in ways that are extremely difficult to predict.
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A wave funneled into a narrowing bay is amplified.
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A wave arriving at a gently sloping shelf pushes much further inland.
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A map meeting a steep coastline may reflect and dissipate.
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So the real answer to how bad an ocean impact would be depends enormously on where in the ocean it lands,
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which coastlines face it, and the shape of the seabed leading up to them.
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An impact in the middle of the South Pacific and an impact in the North Atlantic are entirely different events for humanity.
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And all of that is still only the first of the three disasters.
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Because there is something else coming out of that impact site, and unlike the waves, it does not weaken with distance.
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Remember what happened in the first second.
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A colossal volume of seawater was vaporized instantly.
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That water does not disappear.
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It is thrown into the atmosphere as steam, along with pulverized rock and dust, and, if the impact reaches the sea floor,
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material excavated from the crust itself.
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An ocean impact injects an enormous quantity of water vapor into the upper atmosphere.
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Water vapor is a greenhouse gas.
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Large quantities of it high in the atmosphere can affect the planet's energy balance, and researchers studying ocean impacts have pointed out
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that this is a genuinely distinctive feature of a water strike compared to a land strike.
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There is also the question of what such an injection does to the ozone layer, which shields the surface from ultraviolet radiation.
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So you get competing effects, and the net outcome depends on the size of the impact and the specific conditions.
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The exact magnitude of all this is an area of active research rather than settled fact, And the honest position is
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that the climate consequences of a mid -sized ocean impact are less well understood than the wave effects.
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But the principle is clear.
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An ocean impact is not just a wave -making machine.
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It is also an atmospheric event, and the atmosphere does not stop at any coastline.
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And then there is the third disaster,
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which is the one that would probably kill the most people and it involves no water and no dust at all.
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Imagine the wave has come and gone.
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Imagine it struck a stretch of coastline somewhere in the world, destroying ports, cities, refineries, airports and rail links.
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Now think about what a modern civilization actually is.
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It is a network.
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Food is grown in one place and eaten thousands of kilometers away.
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Medicines are manufactured in a handful of facilities and distributed globally.
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Fuel moves by sea.
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Electronics move by sea.
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A staggering share of everything you own passed through a port at some point.
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And those ports are precisely what a tsunami destroys most efficiently.
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Modern supply chains are also optimized for efficiency rather than resilience.
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Most of what you buy is not sitting in a warehouse waiting for you.
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It is scheduled to arrive shortly before it is needed, because storage costs money.
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That system is extraordinarily efficient and extraordinarily fragile.
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Take out a cluster of major ports on one side of an ocean
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and the effects propagate through that network in ways
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that reach people who never saw the wave and live nowhere near the sea.
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Shortages appear in places that were physically untouched.
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Prices spike.
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Manufacturing stalls because a single component is no longer available.
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We have watched smaller versions of this happen in living memory,
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when a single blocked shipping route or one disrupted factory sent measurable ripples through the global economy for months.
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So the death toll from an ocean impact is not really a question about the height of a wave.
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It is a question about how well a globally interconnected civilization handles losing a section of its coastline.
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And the honest answer is that we do not know, because we have never tested it.
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Now, let us go back to the one that we know actually happened.
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66 million years ago, an object somewhere in the range of 10 to 15 km
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across across struck the earth near what is now the Yucatan Peninsula.
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That was an ocean impact.
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It landed in a shallow sea.
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At that scale, everything I have described stops being a regional disaster and becomes something else entirely.
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The waves generated were beyond anything in human experience,
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and evidence of enormous disturbance in the sediments around the Gulf region records their passage.
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But the waves were not what ended the dinosaurs, and this is the detail that matters most for understanding impact risk.
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The rock at that particular site was rich in sulfur -bearing minerals, and the impact vaporized it and threw it into the atmosphere,
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where it formed a haze that reflected sunlight away from the surface.
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Combined with soot from global wildfires and enormous quantities of dust, the result was a collapse in the sunlight reaching the ground.
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When sunlight fails, photosynthesis fails.
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And when photosynthesis fails, every food chain on the planet that depends on it comes apart from the bottom up.
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Around three -quarters of species on Earth died and every dinosaur larger than a house cat disappeared.
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So the lesson from the only large ocean impact in the record is a strange one.
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The water was not the main weapon, the atmosphere was.
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And that is worth holding on to because it means that when we assess the risk from a future impact,
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the question of what the object hits and what that material does
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when it is thrown into the sky may matter more than whether it lands on land or at sea.
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Here is the genuinely hopeful part, and it is not a small one.
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We are, as far as we know, the first species in the history of this planet with the ability to see one of these coming
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and do something about it.
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There are ongoing
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The following survey programs mapping near -earth objects and the large ones, the civilization -ending kilometer -plus objects,
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are the easiest to find because they are the brightest.
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A substantial proportion of that population has been catalogued
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and none of the known ones are on a collision course in the foreseeable future.
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Objects in the 100 to 300 meter range are much harder to spot, far more numerous and entirely capable of destroying a coastline.
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Those are the ones that could genuinely surprise us.
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That is not a complete planetary defense system, but it is a proof of concept,
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and it moves the whole problem out of the category of things we simply endure.
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The catch is time.
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Deflection works by making a very small change to an object's path a very long way in advance
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so that the tiny nudge compounds into a large miss by the time it reaches us.
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That requires years of warning, which requires finding the object first,
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which brings the entire subject back to something unglamorous.
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The single most valuable thing we can do about asteroid impacts is not build weapons.
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It is look.
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So what would happen if an asteroid hit the ocean.
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For a small object, nothing at all, and nobody would ever know.
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For something a few hundred meters across, a regional catastrophe aimed squarely at the coastlines where we have concentrated our cities,
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our ports, and nearly half of our species,
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followed by an economic disruption that would reach far inland to people who never saw a drop of the water.
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If you enjoyed this, subscribe, because we are only getting started.
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And tell us in the comments whether you think we would actually be ready.
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Watch next as we reconstruct the day the dinosaurs died, hour by hour.
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このレッスンの語彙とスピーキングのポイント
このスピーキングレッスンは、動画「What Would Happen If an Asteroid Hit the Ocean?」を教材にしています。 繰り返し出てくる語は次のとおりです：impact, ocean, wave, object, atmosphere。 この動画には、シャドーイング用の文が193文、単語が2662語あります。 音声の長さは19:59です。 話す速さは1分あたり約133語で安定しており、シャドーイングしやすいペースです。 英語の頻出3,000語に含まれる単語は79%だけなので、語彙は難しめです。
この動画の重要語彙
動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。
| 単語 | 発音 | 意味 |
|---|---|---|
| atmosphere 名詞 | /ˈætməsˌfɪɹ/ | 大気, 大気圏 |
| coastline 名詞 | 海岸線 | |
| disaster 名詞 | /dɪˈzɑːs.təː/ | 災害, 天災 |
| enormous 形容詞 | /ɪˈnɔː.məs/ | 巨大な |
| meter 名詞 | /ˈmitəɹ/ | メーター, 計量器 |
| civilization 名詞 | /ˌsɪv.ɪ.laɪˈzeɪ.ʃən/ | 文明 |
| arrive 動詞 | /əˈɹaɪv/ | 着く, 到着する |
| generate 動詞 | /ˈd͡ʒɛn.ə.ɹeɪt/ | 生む, 生み出す |
| quantity 名詞 | /ˈkwɑn(t)ɪti/ | 量, 数量 |
| dinosaur 名詞 | /ˈdaɪnəsoɹ/ | 恐竜 |
| dust 名詞 | /dʌst/ | 埃, ほこり |
| collapse 動詞 | /kəˈlæps/ | 潰える, 崩壊する |
| collision 名詞 | /kəˈlɪʒn̩/ | 衝突 |
| sunlight 名詞 | /ˈsʌnˌlaɪt/ | 日光, 太陽光 |
| asteroid 名詞 | /ˈæst(ə)ɹɔɪd/ | 小惑星 |
動画に出てくる句動詞
| 単語 | 意味 |
|---|---|
| point out 動詞 | 指す, 指し示す |
| slow down 動詞 | 遅らせる |
| take out 動詞 | 取り出す |
この動画の文法
話し手がよく使っている文型を、動画の実際の表現とともに紹介します。
| 文型 | 動画での表現 |
|---|---|
| 受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる | is crossed · is based · is annihilated |
| 現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している | has meant · have pointed · has come |
| 関係詞節 who / which + 節 — 人や物について情報を加える | water, which means · kilometers, which is · people who never |
注意したい発音
- 「th」の音: earthquake /ˈɝθkweɪk/, myth /mɪθ/, wavelength /ˈweɪvˌlɛŋ(k)θ/, photosynthesis /ˌfoʊ.toʊˈsɪn.θə.sɪs/
- 「sh」と「zh」の音: civilization /ˌsɪv.ɪ.laɪˈzeɪ.ʃən/, collision /kəˈlɪʒn̩/, efficient /ɪˈfɪʃənt/, shallow /ˈʃæloʊ/, shelf /ʃɛlf/
- 長い単語（アクセントの位置に注意）: civilization /ˌsɪv.ɪ.laɪˈzeɪ.ʃən/, genuinely /ˈd͡ʒɛn.ju.ɪn.li/, humanity /hjuˈmænɪti/, planetary /ˈplænɪˌtɛəri/, overwhelmingly /ˌəʊ.vəˈwɛl.mɪŋ.lɪ/
日本語話者が苦手な音：
- /r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: reflect /ɹɪˈflɛkt/, planetary /ˈplænɪˌtɛəri/, regardless /ɹɪˈɡɑɹd.lɪs/, shortly /ˈʃɔɹtli/, carefully /ˈkɛɹf(ə)li/
- /v/ — /b/ にならないように、上の歯を下唇に当てる: civilization /ˌsɪv.ɪ.laɪˈzeɪ.ʃən/, arrive /əˈɹaɪv/, cavity /ˈkæv.ɪt.i/, vapor /ˈveɪpɚ/, overwhelmingly /ˌəʊ.vəˈwɛl.mɪŋ.lɪ/
- /f/ — 「フ」ではなく、上の歯と下唇で出す: atmosphere /ˈætməsˌfɪɹ/, efficient /ɪˈfɪʃənt/, lifetime /ˈlaɪf.taɪm/, reflect /ɹɪˈflɛkt/, handful /ˈhæn(d)fʊl/
この動画での練習方法
- まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
- 通常の速度で一文ずつシャドーイングし、話し手のリズムに合うまで繰り返します。
- 自分の声を録音して元の音声と比べます。atmosphere, coastline, disasterなどの単語に特に注意しましょう。
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。