跟读练习: How Often do Asteroids Hit the Earth?: Crash Course Geology #20 - 通过视频学习英语口语
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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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本课的词汇与口语要点
这段视频共有 150 个句子、1842 个单词可供跟读。 讲话部分时长为 10:15。 说话人语速较快，每分钟约 180 个词，会出现较多连读和弱读。 只有 75% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中 15 个值得学习的单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| asteroid 名词 | /ˈæst(ə)ɹɔɪd/ | 小行星 |
| atmosphere 名词 | /ˈætməsˌfɪɹ/ | 大氣 /大气, 氣圈 /气圈 |
| crater 名词 | /ˈkɹeɪ.tɚ/ | 環形山 /环形山, 撞擊坑 /撞击坑 |
| layer 名词 | /ˈleɪ̯ɚ/ | 層 /层 |
| ton 名词 | /tʌn/ | 噸 /吨, 公噸 /公吨 |
| thin 形容词 | /ˈθɪn/ | бә, 薄 |
| meter 名词 | /ˈmitəɹ/ | 計量表 /计量表 |
| dinosaur 名词 | /ˈdaɪnəsoɹ/ | 恐龍 /恐龙 |
| metre 名词 | /ˈmiːtəɹ/ | 米, 公尺 |
| meteor 名词 | /ˈmiːtiɚ/ | 流星 |
| acid 名词 | /ˈæsɪd/ | 酸 |
| pizza 名词 | /ˈpi.tsə/ | 比薩 /比萨, 披薩 /披萨 |
| belt 名词 | /ˈbɛlt/ | 腰帶 /腰带, 帶 /带 |
| clay 名词 | /kleɪ/ | 黏土 |
| clue 名词 | /kluː/ | 線索 /线索 |
视频中出现的短语动词
| 单词 | 释义 |
|---|---|
| leave behind 动词 | 遺棄 /遗弃 |
| turn out 动词 | 原來 /原来 |
需要注意的发音
说话人用了 31 次缩略和弱读形式，例如 they're, we've, didn't。请按听到的简短形式来说。
- “th” 音: thin /ˈθɪn/, thumb /ˈθʌm/, thirty /ˈθɝti/, earthquake /ˈɝθkweɪk/, altogether /ɔl.tuˈɡɛð.ɚ/
- “sh” 和 “zh” 音: flash /flæʃ/, partially /ˈpɑɹʃəli/, sheer /ʃɪɚ/, collision /kəˈlɪʒn̩/, audition /ɑˈdɪʃən/
- 长单词——注意重音位置: diameter /daɪˈæmɪdɚ/, geology /d͡ʒɪˈɒl.ə.d͡ʒɪ/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, successfully /səkˈsɛs.fə.li/, humanity /hjuˈmænɪti/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 先用 0.75 倍速逐句跟读，熟练之后再回到正常速度。
- 录下自己的声音并与原声对比，特别注意 asteroid, atmosphere, crater 这类单词。
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | is headed · are sometimes called · had been hurled |
| 现在完成时 have/has + 过去分词 — 过去发生但与现在仍有关联的事 | they've collided · You've seen · has just informed |
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。