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中級 米 1744 タグ追加 保存
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動画の字幕をクリックしてすぐ単語の意味を調べられます！
単語帳読み込み中…
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Breaking up is hard to do.
Sometimes, it feels like it goes on forever...days...weeks...months...millions of years?
Just ask Pangaea.
Plate tectonics.
It's not your fault if you take it for granted.
The concept that the Earth's crust moves around, rubs together, and pulls apart seems obvious now.
I mean just look at it.
But as recently as 50 years ago, thinking the continents had ever actually moved from their current locations would have gotten you laughed out of any serious scientific meeting.
The notion of moving continents all started with Alfred Wegener.
He noticed the continents appeared to fit together, almost perfectly, like a jigsaw puzzle.
And if they used to fit together, that means they must have somehow moved apart.
This led him to introduce a new idea: continental drift.
The snug fit of coastlines wasn't the only evidence that the continents were all once joined together in a giant landmass, all nice and cozy.
Wegener noticed fossils of certain animals had been found in Antarctica, India, and Africa.
How did the same animal end up all over the world?
Before, geologists thought land bridges had connected the continents, and were now submerged or eroded away.
Or else, they swam.
Remains of an ancient fern had also been found on five continents.
And ferns definitely can't swim.
It just didn't make sense.
That wasn't all.
The same types of rocks and mountains lined up continuously between continents.
It was a convincing body of evidence suggesting the continents moved around during Earth's history.
So obviously Wegener was celebrated and awarded for this brilliant idea, right?
More like the opposite.
One paleontologist called his theory "Germanic pseudoscience".
He was ridiculed around the world for his "delirious ravings."
The reason for all the hate was no one could see how continents might move.
Did the rotation of the Earth create enough centrifugal force to move them?
Was it the tides?
These forces weren't strong enough to move entire continents.
Wegener was never able to convince other scientists before he died on an expedition to Greenland in 1930 at only 50 years old.
He never knew the fate of his ideas.
In 1929, Arthur Holmes showed thermal convection in the mantle could create enough of a current to move the continental crust on top of it, an idea he originally got from Wegener.
In 1962, geologist Harry Hess found a strange magnetic pattern along a seafloor ridge.
Earth's magnetic field has flipped hundreds of time over the planet's history.
Magnetic minerals deep in the Earth, in hot magma, preserved this magnetic fingerprint as they cooled and hardened into rock.
Just like planetary tree rings, geologists could analyze the rock on either side of the ridge to retrace its history.
The seafloor was spreading apart at these ridges, where new rock was oozing up from the hot mantle.
Geologists finally had proof that earth's crust wasn't static.
It was constantly changing.
They're even moving right now.
Can't you tell?
Probably not.
Every year, the spreading at the Mid-Atlantic ridge pushes the Eurasian plate and North American plate just 2.5 centimeters farther apart.
But over millions of years, that really adds up.
Spreading between plates also happens on land.
The African plate and the Arabian plate are actually splitting the continent in two.
These deep rift valleys will eventually become an ocean and create a new separate African landmass.
The "Ring of Fire" is where denser oceanic crust is moving underneath the less dense continental crust.
90% of the world's earthquakes and most major volcanoes occur along this margin.
Monstrous eruptions and destructive earthquakes change our world everyday and influence the lives of humans all over it.
Just like the surface of our dynamic planet, the story of plate tectonics shows us it can take a little while before earth-shaking ideas change the world.
If you catch my drift.
Stay curious!
コツ：単語をクリックしてすぐ意味を調べられます！

読み込み中…

読み込み中…

中級 米

人はどのようにして大陸プレートの存在を知ったか？　(How Do We Know Plate Tectonics Is Real?)

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Liang Chen 2019 年 5 月 29 日 に公開    newzealand 翻訳    Yukiko チェック

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