Shadowing Practice: How Often do Asteroids Hit the Earth?: Crash Course Geology #20 - Learn English Speaking with Video
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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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Woordenschat en spreektips bij deze les
Deze video bevat 150 zinnen en 1842 woorden om na te spreken. Het gesproken deel duurt 10:15. De spreker praat snel, ongeveer 180 woorden per minuut, dus reken op verbonden en ingeslikte klanken. Slechts 75% van de woorden hoort bij de 3.000 meest gebruikte Engelse woorden, dus de woordenschat is pittig.
Belangrijke woorden in deze video
15 woorden uit de video die het leren waard zijn, met uitspraak en betekenis:
| Woord | Uitspraak | Betekenis |
|---|---|---|
| asteroid zelfstandig naamwoord | /ˈæst(ə)ɹɔɪd/ | planetoïde, asteroïde |
| atmosphere zelfstandig naamwoord | /ˈætməsˌfɪɹ/ | atmosfeer, dampkring |
| crater zelfstandig naamwoord | /ˈkɹeɪ.tɚ/ | krater |
| layer zelfstandig naamwoord | /ˈleɪ̯ɚ/ | laag |
| ton zelfstandig naamwoord | /tʌn/ | ton |
| thin bijvoeglijk naamwoord | /ˈθɪn/ | dun |
| meter zelfstandig naamwoord | /ˈmitəɹ/ | meter, teller |
| dinosaur zelfstandig naamwoord | /ˈdaɪnəsoɹ/ | dinosaurus |
| metre zelfstandig naamwoord | /ˈmiːtəɹ/ | meter |
| meteor zelfstandig naamwoord | /ˈmiːtiɚ/ | meteoor, vallende ster |
| acid zelfstandig naamwoord | /ˈæsɪd/ | zuur |
| pizza zelfstandig naamwoord | /ˈpi.tsə/ | pizza |
| belt zelfstandig naamwoord | /ˈbɛlt/ | gordel, riem |
| roughly bijwoord | /ˈɹʌf.li/ | grofweg |
| clay zelfstandig naamwoord | /kleɪ/ | klei |
Phrasal verbs die je zult horen
| Woord | Uitspraak | Betekenis |
|---|---|---|
| get off werkwoord | van ... afgaan | |
| leave behind werkwoord | achterlaten | |
| stir up werkwoord | /ˈstɜː.ɹʌp/ | opstoken |
| turn out werkwoord | uitvallen, resulteren |
Uitspraak om op te letten
De spreker gebruikt 31 samentrekkingen en verkorte vormen, zoals they're, we've, didn't. Spreek ze kort uit, zoals je ze hoort.
- De “th”-klanken: thin /ˈθɪn/, thumb /ˈθʌm/, thirty /ˈθɝti/, earthquake /ˈɝθkweɪk/, altogether /ɔl.tuˈɡɛð.ɚ/
- De klanken “sh” en “zh”: flash /flæʃ/, partially /ˈpɑɹʃəli/, sheer /ʃɪɚ/, collision /kəˈlɪʒn̩/, audition /ɑˈdɪʃən/
- Lange woorden — let op de klemtoon: diameter /daɪˈæmɪdɚ/, geology /d͡ʒɪˈɒl.ə.d͡ʒɪ/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, successfully /səkˈsɛs.fə.li/, humanity /hjuˈmænɪti/
Zo oefen je met deze video
- Luister de hele video één keer zonder te spreken en noteer de woorden die je niet kent.
- Begin op 0,75× snelheid, spreek zin voor zin na en ga terug naar normale snelheid zodra het makkelijk gaat.
- Neem jezelf op en vergelijk met het origineel; let daarbij op woorden als asteroid, atmosphere, crater.
Grammatica in deze video
De structuren die de spreker het meest gebruikt, met de exacte woorden uit de video:
| Structuur | In de video |
|---|---|
| Lijdende vorm be + voltooid deelwoord — het gaat om wat er gebeurt, niet om wie het doet | is headed · are sometimes called · had been hurled |
| Present perfect have/has + voltooid deelwoord — iets uit het verleden dat nu nog telt | they've collided · You've seen · has just informed |
Wat is de Shadowing-techniek?
Shadowing is een wetenschappelijk onderbouwde taalleermethode die oorspronkelijk is ontwikkeld voor professionele tolkentraining en gepopulariseerd door polyglot Dr. Alexander Arguelles. De methode is eenvoudig maar krachtig: je luistert naar native Engelse audio en herhaalt het onmiddellijk hardop — als een schaduw die de spreker volgt met slechts 1–2 seconden vertraging. In tegenstelling tot passief luisteren of grammaticadrills, dwingt shadowing je hersenen en mondspieren om echte spraakpatronen tegelijkertijd te verwerken en te reproduceren. Onderzoek toont aan dat het de uitspraaknauwkeurigheid, intonatie, ritme, verbonden spraak, luisterbegrip en spreekvaardigheid aanzienlijk verbetert — waardoor het een van de meest effectieve methoden is voor IELTS Speaking-voorbereiding en echte Engelse communicatie.