शैडोइंग अभ्यास: How Often do Asteroids Hit the Earth?: Crash Course Geology #20 - वीडियो के साथ अंग्रेजी बोलना सीखें

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The sky is falling!

Sort of?

Our planet gets pummeled by about 48 .5 tons of space rocks every day.

That's a weight of seven and a half elephants falling from the heavens 24 -7.

Most of that cosmic debris is harmless.

It's so tiny it burns up in the atmosphere before it rains down on Earth.

But what about the really big rocks?

The asteroids that could wipe out life as we know it?

Truth is, they're out there, and they've collided with Earth before.

Today, let's talk straight about rocks from space.

They're at the top of my things to worry about list.

Hi, I'm Sage, and this is Crash Course Geology.

You've seen the movies.

An asteroid is headed straight for Earth.

Everybody panic, crunch for your lives.

Aw, thanks, Duane.

I really should go out on more movie auditions.

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.

Most of the time.

So what exactly are they? it.

Most space rocks are leftovers from the moment our solar system formed, some 4 .6 billion years ago.

We differentiate them in a few ways.

An asteroid is a rock that orbits the sun and is more than one meter across.

Basically, anything with a diameter longer than a baseball bat, but not big enough to be a planet with its own gravitational pull.

That's why asteroids are sometimes called a minor planet.

Mmm, burn!

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.

A trip to the asteroid belt would be like, uh, what am I thinking of?

Oh, that video game where you dodge barrels that a gorilla throws at you.

Uh, Dwayne has just informed me that there's a video game literally called Asteroids, and apparently it's very famous.

Mm, my bad.

Now, when a space rock's diameter is less than a meter across, it's a meteoroid.

Usually, a meteoroid is a chunk of an asteroid that got blasted off during a collision with another asteroid.

You'd think that wouldn't happen with all that, you know, space, but it does.

So, big space rock?

Asteroid.

Small space rock?

Meteoroid.

And if a meteoroid leaves space and enters a planet's atmosphere, it becomes a meteor.

These are the flashes of light we spot in the sky and call shooting stars.

Meteors are little space rocks that burn up and vaporize into dust as they hurtle through the atmosphere.

If a piece of meteor doesn't completely obliterate before reaching the ground, it becomes something else.

A meteorite.

As for asteroids that enter the Earth's atmosphere or hit the surface, they're still called asteroids.

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.

In Alabama in 1954, a meteorite broke through Ann Hodge's roof, interrupted her nap, and left her a mean shiner on her thigh.

And most of the space rocks that hit Earth aren't big enough to completely wreck it.

If an asteroid less than 25 meters wide enters Earth's atmosphere, it's likely to burn up and disintegrate.

In fact, an asteroid the size of a car enters the atmosphere and explodes before reaching the surface almost every year.

That's what happened above Chelyabinsk, Russia in 2013, with an asteroid about two and a half times as long as a London bus.

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.

And the sound wave that followed was so powerful, it shattered windows across six cities, injuring 1 ,500 people.

So even asteroids that burn up can have an impact, especially if they're big.

An asteroid 140 meters wide hits the Earth roughly every 20 ,000 years.

That's big enough to wipe out a metro area or even whole U .S states.

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.

But it does happen.

And we know that because it's happened before.

Let's dig a little deeper.

Remember, 66 million years ago, an asteroid wider than Mount Everest is tall, hurtled through Earth's atmosphere.

And it didn't burst in midair.

It directly collided with our planet off the coast of what's now Mexico.

And the world changed.

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,

vaporizing some of the rocks and water around it.

Within three minutes, its sheer force caused the ground in the center of the crater to liquefy

and rebound up into a giant peak.

Then it collapsed again, sending out shockwaves in every direction.

That collapse dumped chunks of rock at the edges of the crater, forming a ring around the molten gap at the center.

And that's just the first thirty minutes.

Within an hour, the ocean surged over the molten crater where the water began churning and spitting up steam.

For a whole day, the ocean sloshed back and forth as rocks from the crater's rim toppled and stirred up water,

waves spitting them back onto the crater's rim.

Also, everything within 1 ,400 kilometers of the impact was on fire.

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.

And there was a massive tsunami, with waves 1 .5 kilometers high.

The shockwave then triggered more tsunamis, earthquakes, and volcanic eruptions across the globe.

If that wasn't enough, the rocks vaporized by the asteroid's impact unleashed up to 325 gigatons of sulfur into the air,

creating toxic sulfuric acid.

This might have blocked the sun and chilled the climate for years

or tainted the rivers and oceans with showers of acid rain.

All told, these effects were eventually enough to kill roughly 75 % of all plants and animals on Earth, including the dinosaurs.

Except the very few that evolved into today's birds.

Those guys are resilient.

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?

Has anyone seen my keys?

To be fair, it took decades of shared brain power to get to this level of detail.

In 1977, an American father and son team, Luis and Walter Alvarez, made a discovery.

In Italy, they found a very thin layer of clay sandwiched between rocks with tons of marine fossils, and rocks with barely any.

It turns out you can find this thin clay layer in rocks from the same time period all over the world.

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.

This was the first clue.

All that iridium must have been ejected from a space rock.

A really big space rock.

Today, that thin layer is called the Cretaceous -Paleogene boundary, or the KPG boundary for short.

It marks the moment about 66 million years ago

when a 12 -kilometer asteroid rammed into the planet and left a geological stamp.

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.

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.

100

So it wasn't even discovered until the 1990s.

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Chicxulub?

102

Can't see me.

103

It's pretty much impossible to find evidence of asteroid impacts from that long ago.

104

Erosion and plate tectonics are constantly exfoliating Earth in slo -mo, erasing the evidence.

105

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.

108

It's a dome, an area where the ground lifted after an asteroid obliterated the ground surrounding it.

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Hmm?

110

Oh, yeah, Dwayne doesn't like that I use the word obliterated.

111

If you're wondering how worried you should be about an asteroid doing the same thing to us, you're not alone.

112

But I have more good news.

113

We've got one thing the dinosaurs didn't have.

114

What's that, Dwayne?

115

Chapel Rhone?

116

Well, yes, definitely.

117

Oh, thumbs?

118

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.

120

Remember how I said that before?

121

That's foreshadowing, baby.

122

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.

124

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.

125

If an asteroid does someday pose a threat, we'll know!

126

And there's an organized effort to prepare for these risks if they ever arise.

127

Every two years, NASA's planetary defense team leads a hypothetical tabletop exercise where key leaders

128

and experts run through the what -ifs of a potential asteroid impact.

129

Someone should tell them to play that asteroids game I just learned about.

130

There's also ongoing research into redirecting an asteroid's path by crashing a spacecraft into it.

131

And get this, we've done it!

132

Like not in a movie, in real life!

133

NASA sent a spacecraft on a one -way trip to smack into an asteroid.

134

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.

136

But it successfully head -butted the 160 -meter rock onto a slightly different path.

137

That's one small smack on an asteroid, one giant leap for humanity.

138

So the sky is falling.

139

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.

141

But altogether, their total mass is less than that of our moon.

142

And there's even more good news.

143

The last time a large asteroid had a major impact, some life managed to survive, adapt, and evolve into new life forms,

144

including a weird, complicated ape that's invented marbles like novelty socks, pizza with cheese in the crust,

145

and ways of tracking asteroids before they become a threat.

146

All right, can we strike asteroid impact from my things to worry about list?

147

Presently, it is directly above the server being mad at me because I corrected my order.

148

You're not mad at me, are you, Katie?

149

Next time, we'll learn how geology fuels our world.

150

See you then.

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इस पाठ की शब्दावली और बोलने के सुझाव

इस वीडियो में शैडोइंग के लिए 150 वाक्य और 1842 शब्द हैं। बोला गया हिस्सा 10:15 लंबा है। वक्ता तेज़ बोलता है, लगभग 180 शब्द प्रति मिनट, इसलिए जुड़ी हुई और कमज़ोर ध्वनियाँ ज़्यादा मिलेंगी। केवल 75% शब्द अंग्रेज़ी के 3,000 सबसे आम शब्दों में से हैं, इसलिए शब्दावली कठिन है।

इस वीडियो की मुख्य शब्दावली

वीडियो के 15 सीखने लायक शब्द, उच्चारण और अर्थ के साथ:

शब्द	उच्चारण	अर्थ
asteroid संज्ञा	/ˈæst(ə)ɹɔɪd/	क्षुद्रग्रह, उपग्रह
atmosphere संज्ञा	/ˈætməsˌfɪɹ/	वायुमण्डल, वायुमंडल
crater संज्ञा	/ˈkɹeɪ.tɚ/	गर्त, दहाना
layer संज्ञा	/ˈleɪ̯ɚ/	परत, तह
ton संज्ञा	/tʌn/	टन
thin विशेषण	/ˈθɪn/	पतला, दुबला
dinosaur संज्ञा	/ˈdaɪnəsoɹ/	डायनासोर, डायनोसोर
metre संज्ञा	/ˈmiːtəɹ/	मीटर
meteor संज्ञा	/ˈmiːtiɚ/	उल्का
acid संज्ञा	/ˈæsɪd/	अम्ल, एसिड
pizza संज्ञा	/ˈpi.tsə/	पिज़ा, पिज़्ज़ा
belt संज्ञा	/ˈbɛlt/	पेटी, बेल्ट
clay संज्ञा	/kleɪ/	मृत्तिका, चिकनी मिट्टी
clue संज्ञा	/kluː/	संकेत
collapse क्रिया	/kəˈlæps/	गिरना

ध्यान देने योग्य उच्चारण

वक्ता 31 बार संक्षिप्त रूपों का प्रयोग करता है, जैसे they're, we've, didn't। इन्हें वैसे ही छोटा बोलें जैसा आप सुनते हैं।

“th” की ध्वनियाँ: thin /ˈθɪn/, thumb /ˈθʌm/, thirty /ˈθɝti/, earthquake /ˈɝθkweɪk/, altogether /ɔl.tuˈɡɛð.ɚ/
“sh” और “zh” की ध्वनियाँ: flash /flæʃ/, partially /ˈpɑɹʃəli/, sheer /ʃɪɚ/, collision /kəˈlɪʒn̩/, audition /ɑˈdɪʃən/
लंबे शब्द — बलाघात सही रखें: diameter /daɪˈæmɪdɚ/, geology /d͡ʒɪˈɒl.ə.d͡ʒɪ/, complicated /ˈkɑm.plɪˌkeɪ.tɪd/, successfully /səkˈsɛs.fə.li/, humanity /hjuˈmænɪti/

इस वीडियो से अभ्यास कैसे करें

पहले बिना बोले पूरा वीडियो एक बार सुनें और जो शब्द नहीं आते उन्हें लिख लें।
0.75× गति से शुरू करें, एक-एक वाक्य की शैडोइंग करें, और सहज लगने पर सामान्य गति पर लौटें।
अपनी आवाज़ रिकॉर्ड करें और मूल से तुलना करें, ख़ासकर asteroid, atmosphere, crater जैसे शब्दों पर ध्यान दें।

इस वीडियो का व्याकरण

वक्ता जिन संरचनाओं का सबसे अधिक प्रयोग करता है, वीडियो के असली शब्दों के साथ:

संरचना	वीडियो में
Passive voice be + past participle — ज़ोर इस पर कि क्या होता है, न कि कौन करता है	is headed · are sometimes called · had been hurled
Present perfect have/has + past participle — बीता हुआ काम जिसका असर अभी भी है	they've collided · You've seen · has just informed

शैडोइंग तकनीक क्या है?

शैडोइंग (Shadowing) एक विज्ञान-समर्थित भाषा सीखने की तकनीक है जो मूल रूप से पेशेवर दुभाषिया प्रशिक्षण के लिए विकसित की गई थी। विधि सरल लेकिन शक्तिशाली है: आप मूल अंग्रेज़ी ऑडियो सुनते हैं और तुरंत इसे ज़ोर से दोहराते हैं — जैसे वक्ता की छाया 1-2 सेकंड की देरी से। शोध से पता चलता है कि यह उच्चारण सटीकता, स्वर, लय, जुड़ी हुई ध्वनियाँ, सुनने की समझ और बोलने की प्रवाहशीलता में काफ़ी सुधार करता है।

शैडोइंग तकनीक: पूरी चरण-दर-चरण गाइड पढ़ें →

शैडोइंग अभ्यास: How Often do Asteroids Hit the Earth?: Crash Course Geology #20 - वीडियो के साथ अंग्रेजी बोलना सीखें

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शैडोइंग तकनीक क्या है?