ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: Where Do Diamonds Come From?: Crash Course Geology #8

In the Smithsonian Museum of Natural History lies a mysterious object.

It's drawn millions of visitors from across the world.

And not just for its beauty, but for its curse.

I'm talking about this.

The Hope Diamond.

A gem taken from India in the 1660s whose various owners

are rumored to have mysteriously died from everything from wild dog attacks to beheadings.

Shh.

It's okay, Dwayne.

The scary gem is safe in a museum. For now.

The Hope Diamond's curse might be a myth.

But one thing's for sure, it's not the only myth out there about diamonds.

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

Diamonds.

They're bright, flawless, and a girl's best friend.

These aren't real, by the way.

What do you think, rocks are made of money?

But to a geologist, diamonds are much more than a symbol of glamour, timelessness, and love.

And there are a lot of misconceptions about them.

Starting with their structure.

Diamond is a clear mineral made of one main ingredient.

Carbon.

Although sometimes small amounts of other elements can give them different color, like that deep hue in the Hope Diamond comes from boron.

While carbon itself is a pretty common element, diamonds do something special with it.

The carbon atoms are puzzled together super tightly into a crystal structure that's nearly indestructible.

In fact, diamond is the hardest naturally occurring substance on Earth.

So hard we use it to cut through concrete and stone.

But how do you get a structure like that?

Spoiler alert, not from coal!

You've probably heard that myth before, that diamonds are made of a lump of coal and a lot of pressure.

A great motivational metaphor, but not a scientifically accurate one.

Sure, coal is also made of carbon, but the way diamonds actually form is way cooler than squishing a sooty rock.

Let's dig a little deeper.

For hundreds of years, humans didn't know where diamonds came from.

We could only find them by searching riverbeds for washed away sediment, also known as alluvial mining.

But there was no way of knowing what type of rock they came from.

Until 1870, when miners in South Africa struck gold, or, well, diamond.

In the town of Kimberley, they found tons of diamonds, not on the riverbed, but in the ground.

It was the first time diamonds had ever been found in the volcanic rock they came from.

The discoverers named the source rock Kimberlite after the town and started to study it.

And after a hundred odd years, we finally figured out how those special stones got there.

It turns out diamonds form in cratons, the deep down roots of continents.

They're stable, hot, and pressurized enough to form carbon into that super dense crystal structure that diamonds are known for.

Most diamonds form in Earth's upper mantle, the part right below the outer crust.

But some diamonds, like the Hope Diamond, form even deeper down, in the transition zone and the lower mantle,

more than 600 kilometers below the surface.

Maybe that's why the Hope Diamond is allegedly cursed.

It's seen things no one was ever meant to see.

So how do they get to the surface?

With a Ba-bang!

When continents break apart, they disrupt the mantle, leading to a millions of years long domino effect.

Eventually carbon dioxide and water trapped within deep pockets of magma explode into powerful kimberlite eruptions.

Molten rocks shoot upward, blasting out carrot-shaped pipes through the surface.

And the violent flow rips up chunks of deep rock that, if you're lucky, are studded with diamonds.

As for super deep diamonds like the Hope, they have to rise a bit higher in the mantle first, possibly by hitching a ride on an extra hot rock that flows from the lower mantle to the upper.

Then kimberlite eruptions can blast them to the surface.

Most kimberlite eruptions happened between 250 and 50 million years ago, and their diamonds started forming long before the blasts,

up to three billion years ago.

Talk about classic rock.

That one was so bad it's good.

Which helps us see diamonds for what they really are, time capsules of the past.

They have a lot to teach us about the super deep Earth and its super long geologic history.

Mineral and fluid inclusions trapped in diamond can give us clues about what the mantle was like back when they formed, which has helped geologists unravel all kinds of geologic mysteries.

Like Dr. Kate Kaseyeva has examined garnet inclusions in diamonds using

advanced scientific tools to get more information about the composition of the deep mantle.

The last kimberlite eruption was 13 million years ago, and we don't know if another will ever happen again.

So while diamonds continue to grow deep underground, we're left to mind the ones that ancient eruptions have already lofted into Earth's crust.

That may have given you the impression that diamonds are super rare.

After all, we humans have prized them for centuries, and there's only so many that are accessible to us.

But diamonds' rarity is also a myth, largely perpetuated by a corporation.

We'll get to that in a sec.

It's true that we valued diamonds for hundreds, if not thousands, of years.

And at first, they were scarce enough that only royalty and the extremely wealthy owned them.

Like, by 1668, the Hope Diamond had reached the hands of the French King Louis XIV, who would later die of gangrene.

Finding the Kimberlite diamonds in South Africa had huge effects.

For the next almost century, the African continent produced 98% of all the diamonds in the world.

And with so many diamonds flooding the market, they weren't just for royalty anymore.

And that's when British finance bureau Cecil Rhodes saw an opportunity.

He bought shares in a bunch of diamond mines and eventually controlled enough of them to form the De Beers Mining Company.

By 1887, the company owned every diamond mine in South Africa.

For the next seven decades, it controlled just about every diamond mine in the world.

De Beers used its monopoly to keep up the illusion that diamonds were scarce, a perception that sold tons of overpriced diamonds.

By the 2000s, De Beers finally lost their monopoly, but the myth that diamonds are rare has stuck around.

Despite the fact that they're more commonly found than lots of other gems.

Today, diamond value can be determined by the four C's.

Color, Clarity, Cut, and Carat Weight, which tell us what diamond crystals look like, how they're cut, and how big they are.

For example, the average diamond stud earring is between 0.25 and 1 carat, which can roughly range from a few hundred to a few thousand dollars based on the type of diamond.

By comparison, the Hope Diamond is a whopping 45.52 carats,

which is why it's valued at up to 350 million dollars.

But those ordinary diamond studs might not be made of natural diamonds at all.

Which brings me to our last myth.

While many may think that lab-grown diamonds are fake, they are in fact very much real.

See, in the 1940s, scientists at General Electric started working on a way to skip the whole billion-year mantle-to-mine timeline

and grow diamonds in the lab instead.

The effort was called Project Super Pressure.

Coincidentally, that's also what I called my all-night study sessions in college.

The scientists put some graphite, which is also made of carbon, under super intense heat and pressure.

And in just a few weeks, they had made their own diamond.

In fact, it sort of worked the same way many people think coal turns into diamonds.

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No, Duane, you're granite.

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You can't turn into a diamond.

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No, even if I press on you really hard.

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Within a couple decades, lab-grown diamonds were just as hard, sparkly, and impressive as the originals.

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Modern processes used tiny fragments of natural diamonds to seed new, lab-grown ones and work way more efficiently than the old techniques.

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Lab-grown diamonds are real diamonds, they just have a slightly different origin story.

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Today, lab-grown diamonds are more popular than ever.

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For one, they are way cheaper than natural diamonds, costing up to 85% less than their counterparts.

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Plus, many people, myself very much included, Consider lab-grown diamonds a much more ethical purchase.

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Diamond mines severely damage the environment.

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The Big Hole Mine in Kimberley can literally be seen from space and contributes to all sorts of environmental problems,

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from erosion to water pollution.

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And importantly, conditions in diamond mines can be terribly dangerous for the miners themselves.

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That's especially the case in places with less social stability, like parts of Central and West Africa, where regional conflicts cut communities off from their social and resource networks.

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In those places, small-scale mining operations often use forced and child labor and sell diamonds to fund violent conflicts.

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We call those blood diamonds.

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Even though international organizations have tried to crack down on them, they're still out there in the diamond market.

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Now that's a deeply complex topic, So check out the links below to learn even more.

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Some folks still make a case for natural diamonds, saying that diamond mining can be good for local economies in some of the world's poorest countries,

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and that's less environmentally harmful than other kinds of mining.

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So yeah, there are lots of cultural, political, and environmental factors at play when choosing a lab-grown or natural diamond.

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But geologically speaking, they're one and the same.

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Whether they're grown in a lab or blasted from the Earth's mantle, Diamonds are part of our world.

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And they're not just nice to look at.

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They're remnants of volcanic eruptions that happened millions of years ago.

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They unravel mysteries about deep earth and deep time.

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They're so hard they beat rock and rock-paper-scissors every time.

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And maybe they're cursed.

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At least the Hope Diamond.

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Dwayne!

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Next time, we'll talk about another force to be reckoned with.

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Water.

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See you then!

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Thanks for watching this episode of Crash Course Geology, which was filmed at our studio in Indianapolis, Indiana, and was made with the help of these glittering glorious people.

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If you want to help keep Crash Course free for everyone forever, you can join our community on Patreon.

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ฝึกพูดภาษาอังกฤษด้วยเทคนิค Shadowing จากวิดีโอ: Where Do Diamonds Come From?: Crash Course Geology #8

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