シャドーイング練習: How Often do Asteroids Hit the Earth?: Crash Course Geology #20 - 動画で英語スピーキングを学ぶ
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150 文
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The sky is falling!
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Sort of?
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Our planet gets pummeled by about 48 .5 tons of space rocks every day.
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That's a weight of seven and a half elephants falling from the heavens 24 -7.
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Most of that cosmic debris is harmless.
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It's so tiny it burns up in the atmosphere before it rains down on Earth.
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But what about the really big rocks?
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The asteroids that could wipe out life as we know it?
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Truth is, they're out there, and they've collided with Earth before.
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Today, let's talk straight about rocks from space.
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They're at the top of my things to worry about list.
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Hi, I'm Sage, and this is Crash Course Geology.
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You've seen the movies.
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An asteroid is headed straight for Earth.
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Everybody panic, crunch for your lives.
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Aw, thanks, Duane.
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I really should go out on more movie auditions.
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But despite all that drama and disaster, space rocks are sort of run -of -the -mill here on Earth, hitting its surface daily like a light drizzle.
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Most of the time.
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So what exactly are they? it.
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Most space rocks are leftovers from the moment our solar system formed, some 4 .6 billion years ago.
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We differentiate them in a few ways.
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An asteroid is a rock that orbits the sun and is more than one meter across.
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Basically, anything with a diameter longer than a baseball bat, but not big enough to be a planet with its own gravitational pull.
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That's why asteroids are sometimes called a minor planet.
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Mmm, burn!
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Most asteroids hail from the asteroid belt, an area between Mars and Jupiter that's chock -full of space rocks, some of them hundreds of miles across.
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A trip to the asteroid belt would be like, uh, what am I thinking of?
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Oh, that video game where you dodge barrels that a gorilla throws at you.
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Uh, Dwayne has just informed me that there's a video game literally called Asteroids, and apparently it's very famous.
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Mm, my bad.
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Now, when a space rock's diameter is less than a meter across, it's a meteoroid.
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Usually, a meteoroid is a chunk of an asteroid that got blasted off during a collision with another asteroid.
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You'd think that wouldn't happen with all that, you know, space, but it does.
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So, big space rock?
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Asteroid.
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Small space rock?
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Meteoroid.
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And if a meteoroid leaves space and enters a planet's atmosphere, it becomes a meteor.
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These are the flashes of light we spot in the sky and call shooting stars.
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Meteors are little space rocks that burn up and vaporize into dust as they hurtle through the atmosphere.
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If a piece of meteor doesn't completely obliterate before reaching the ground, it becomes something else.
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A meteorite.
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As for asteroids that enter the Earth's atmosphere or hit the surface, they're still called asteroids.
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But here's some good news while our planet gets pelted by tons of space rocks every day, there's only one recorded instance of a meteorite actually striking a person.
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In Alabama in 1954, a meteorite broke through Ann Hodge's roof, interrupted her nap, and left her a mean shiner on her thigh.
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And most of the space rocks that hit Earth aren't big enough to completely wreck it.
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If an asteroid less than 25 meters wide enters Earth's atmosphere, it's likely to burn up and disintegrate.
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In fact, an asteroid the size of a car enters the atmosphere and explodes before reaching the surface almost every year.
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That's what happened above Chelyabinsk, Russia in 2013, with an asteroid about two and a half times as long as a London bus.
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It entered Earth's atmosphere and burned up 30 kilometers above the city, releasing 30 times more energy than the atomic bomb dropped on Hiroshima.
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And the sound wave that followed was so powerful, it shattered windows across six cities, injuring 1 ,500 people.
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So even asteroids that burn up can have an impact, especially if they're big.
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An asteroid 140 meters wide hits the Earth roughly every 20 ,000 years.
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That's big enough to wipe out a metro area or even whole U .S states.
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An asteroid with the potential to cause global devastation and kill most living things is extremely rare, reaching us every 100 million years at most.
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But it does happen.
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And we know that because it's happened before.
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Let's dig a little deeper.
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Remember, 66 million years ago, an asteroid wider than Mount Everest is tall, hurtled through Earth's atmosphere.
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And it didn't burst in midair.
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It directly collided with our planet off the coast of what's now Mexico.
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And the world changed.
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In the first minute of impact, what's now known as the Chicxulub asteroid carved a crater over 20 kilometers deep into the ocean floor,
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vaporizing some of the rocks and water around it.
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Within three minutes, its sheer force caused the ground in the center of the crater to liquefy
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and rebound up into a giant peak.
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Then it collapsed again, sending out shockwaves in every direction.
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That collapse dumped chunks of rock at the edges of the crater, forming a ring around the molten gap at the center.
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And that's just the first thirty minutes.
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Within an hour, the ocean surged over the molten crater where the water began churning and spitting up steam.
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For a whole day, the ocean sloshed back and forth as rocks from the crater's rim toppled and stirred up water,
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waves spitting them back onto the crater's rim.
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Also, everything within 1 ,400 kilometers of the impact was on fire.
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25 trillion tons of debris had been hurled up into the sky, some of which landed far from the crater, setting fires ablaze all over the planet.
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And there was a massive tsunami, with waves 1 .5 kilometers high.
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The shockwave then triggered more tsunamis, earthquakes, and volcanic eruptions across the globe.
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If that wasn't enough, the rocks vaporized by the asteroid's impact unleashed up to 325 gigatons of sulfur into the air,
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creating toxic sulfuric acid.
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This might have blocked the sun and chilled the climate for years
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or tainted the rivers and oceans with showers of acid rain.
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All told, these effects were eventually enough to kill roughly 75 % of all plants and animals on Earth, including the dinosaurs.
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Except the very few that evolved into today's birds.
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Those guys are resilient.
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Can we just appreciate for a moment that human brain power can reconstruct a thing that happened millions of years ago, but I can't remember where I left my keys?
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Has anyone seen my keys?
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To be fair, it took decades of shared brain power to get to this level of detail.
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In 1977, an American father and son team, Luis and Walter Alvarez, made a discovery.
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In Italy, they found a very thin layer of clay sandwiched between rocks with tons of marine fossils, and rocks with barely any.
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It turns out you can find this thin clay layer in rocks from the same time period all over the world.
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The Alvarezes and their collaborators discovered that this layer is full of soot and iridium, an extremely rare metal on Earth, most often found in asteroids.
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This was the first clue.
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All that iridium must have been ejected from a space rock.
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A really big space rock.
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Today, that thin layer is called the Cretaceous -Paleogene boundary, or the KPG boundary for short.
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It marks the moment about 66 million years ago
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when a 12 -kilometer asteroid rammed into the planet and left a geological stamp.
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The other big piece of evidence was the Chicxulub impact crater, which marks the spot where the asteroid hit just off the coast of what's now Mexico.
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It's a whopping 180 kilometers wide and 900 meters deep, but it's also buried a kilometer below the surface, partially under the ocean.
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So it wasn't even discovered until the 1990s.
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Chicxulub?
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Can't see me.
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It's pretty much impossible to find evidence of asteroid impacts from that long ago.
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Erosion and plate tectonics are constantly exfoliating Earth in slo -mo, erasing the evidence.
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Like, the Fredafort impact structure in what's now South Africa marks
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a spot where an asteroid up to 25 kilometers wide slammed into the Earth a little over 2 billion years ago.
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But the main clue left behind isn't even a crater anymore.
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It's a dome, an area where the ground lifted after an asteroid obliterated the ground surrounding it.
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Hmm?
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Oh, yeah, Dwayne doesn't like that I use the word obliterated.
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If you're wondering how worried you should be about an asteroid doing the same thing to us, you're not alone.
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But I have more good news.
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We've got one thing the dinosaurs didn't have.
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What's that, Dwayne?
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Chapel Rhone?
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Well, yes, definitely.
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Oh, thumbs?
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I think you could argue Iguanodons did have thumbs but we're getting off track here.
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We've got one thing the dinosaurs didn't have, and that's human brain power.
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Remember how I said that before?
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That's foreshadowing, baby.
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Over the years, we've developed different ways of tracking asteroids, like their pizzas we never want delivered.
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Today, NASA uses powerful space telescopes to take pictures of asteroids' movements and calculate their orbits.
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And none of the asteroids big enough to be damaging—let me repeat, none of them— are on track to hit the Earth any time in the foreseeable future.
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If an asteroid does someday pose a threat, we'll know!
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And there's an organized effort to prepare for these risks if they ever arise.
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Every two years, NASA's planetary defense team leads a hypothetical tabletop exercise where key leaders
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and experts run through the what -ifs of a potential asteroid impact.
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Someone should tell them to play that asteroids game I just learned about.
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There's also ongoing research into redirecting an asteroid's path by crashing a spacecraft into it.
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And get this, we've done it!
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Like not in a movie, in real life!
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NASA sent a spacecraft on a one -way trip to smack into an asteroid.
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And it worked.
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The craft, called the Double Asteroid Redirection Test, or DART, had to travel for more than 10 months to reach the asteroid.
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But it successfully head -butted the 160 -meter rock onto a slightly different path.
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That's one small smack on an asteroid, one giant leap for humanity.
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So the sky is falling.
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But it's far more likely to be a shower of cosmic brownie sprinkles than a massive dino killer.
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At the time we're filming this, there are almost 1 .5 million asteroids in our solar system that we know of.
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But altogether, their total mass is less than that of our moon.
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And there's even more good news.
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The last time a large asteroid had a major impact, some life managed to survive, adapt, and evolve into new life forms,
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including a weird, complicated ape that's invented marbles like novelty socks, pizza with cheese in the crust,
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and ways of tracking asteroids before they become a threat.
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All right, can we strike asteroid impact from my things to worry about list?
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Presently, it is directly above the server being mad at me because I corrected my order.
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You're not mad at me, are you, Katie?
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Next time, we'll learn how geology fuels our world.
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See you then.
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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
この動画には、シャドーイング用の文が150文、単語が1842語あります。 音声の長さは10:15です。 話す速さは速く、1分あたり約180語です。音のつながりや弱く発音される音が多くなります。 英語の頻出3,000語に含まれる単語は75%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 |
|---|---|---|
| asteroid 名詞 | /ˈæst(ə)ɹɔɪd/ | 小惑星 |
| atmosphere 名詞 | /ˈætməsˌfɪɹ/ | 大気, 大気圏 |
| crater 名詞 | /ˈkɹeɪ.tɚ/ | クレーター, 隕石孔 |
| layer 名詞 | /ˈleɪ̯ɚ/ | 層, 膜 |
| ton 名詞 | /tʌn/ | トン |
| thin 形容詞 | /ˈθɪn/ | 薄い, 細い |
| meter 名詞 | /ˈmitəɹ/ | メーター, 計量器 |
| dinosaur 名詞 | /ˈdaɪnəsoɹ/ | 恐竜 |
| metre 名詞 | /ˈmiːtəɹ/ | メートル, ㍍ |
| meteor 名詞 | /ˈmiːtiɚ/ | 流星, 流れ星 |
| acid 名詞 | /ˈæsɪd/ | 酸 |
| pizza 名詞 | /ˈpi.tsə/ | ピザ, ピッツァ |
| belt 名詞 | /ˈbɛlt/ | ベルト |
| clay 名詞 | /kleɪ/ | 粘土 |
| clue 名詞 | /kluː/ | 手掛かり, 切っ掛け |
動画に出てくる句動詞
| 単語 | 意味 |
|---|---|
| wipe out 動詞 | 一掃する |
| get off 動詞 | 降りる |
| leave behind 動詞 | 置き忘れる |
注意したい発音
話し手はthey're, we've, didn'tなど、短縮形や弱形を31回使っています。聞こえたとおりの短い形で発音しましょう。
- 「th」の音: thin /ˈθɪn/, thumb /ˈθʌm/, thirty /ˈθɝti/, earthquake /ˈɝθkweɪk/, altogether /ɔl.tuˈɡɛð.ɚ/
- 「sh」と「zh」の音: flash /flæʃ/, partially /ˈpɑɹʃəli/, sheer /ʃɪɚ/, collision /kəˈlɪʒn̩/, audition /ɑˈdɪʃən/
- 長い単語（アクセントの位置に注意）: diameter /daɪˈæmɪdɚ/, geology /d͡ʒɪˈɒl.ə.d͡ʒɪ/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, successfully /səkˈsɛs.fə.li/, humanity /hjuˈmænɪti/
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。
- まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
- 自分の声を録音して元の音声と比べます。asteroid, atmosphere, craterなどの単語に特に注意しましょう。
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 headed · are sometimes called · had been hurled |
| 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 | they've collided · You've seen · has just informed |
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。