シャドーイング練習: What’s at the center of the earth?: Crash Course Geology #4 - 動画で英語スピーキングを学ぶ
レッスンを作成中...
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It was the spring of 1967 and the Cold War was underway.
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The US was on high alert for attacks coming from the Soviet Union.
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And on May 23rd, the radio communications suddenly jammed.
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Did the USSR bug the system?
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Was this an act of war?
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A fleet of US Air Force bombers was poised to launch a counterattack.
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An act that might have sparked nuclear war.
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But just in time, vital information was relayed by an unlikely group.
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Weather forecasters?
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Hi, I'm Sage.
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This is Crash Course Geology.
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No, you didn't accidentally click on a Crash Course US History video.
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To understand what really happened during the Cold War, we've got to dig deep, all the way to the Earth's core, the hot, dense center of the planet.
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Last time, we learned about the Earth's top two layers, the tough crust and the taffy-like mantle.
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But for a long time, we could only imagine what was at the center of this big blue marble.
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Back in 1692, Edmund Halley was the first to describe Earth's core as something separate and disconnected from its shell.
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He described an internal structure known as the hollow-Earth model where a series of hollow spheres rotated around a central core.
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He argued that both Earth's shell and core had something called a magnetic field, each with two poles, or points of attraction and repulsion.
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Think of the magnets on your fridge.
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The same forces that draw a magnet to the fridge and push two magnets apart, make up a magnetic field.
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But Halley wasn't quite right.
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He based his theory on Newton's calculations of the density of the Earth and the Moon.
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Which were off.
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Look, Newton basically invented physics.
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It's okay for him to take an L once in a while.
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Hundreds of years later, scientists developed the field of seismology to study Earth's insights.
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Tracking seismic waves within the Earth helped British geologist Richard Oldham find the first evidence of Earth's core in 1906,
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and led British physicist Harold Jeffries to suggest that the core might be liquid 20 years later.
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It took another decade to discover what was really at the heart of our home planet, thanks to one of my geology rock stars.
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Hit it, Dwayne!
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When Inga Lehmann was growing up in late 19th century Denmark, most people didn't expect much of a girl's, but that didn't hold her back.
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As a kid, Lehmann attended a progressive co-ed school in Copenhagen, but she didn't find the same egalitarian attitudes when she studied math at the University of Cambridge in England.
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Women could attend lectures, but they couldn't officially enroll or use labs or libraries.
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And while she eventually finished her math degree in Denmark, what she really was interested in was earthquakes.
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In the late 1920s and 30s, Lehmann filled index cards with information about earthquakes from all over the world, looking them over in her garden,
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storing them in empty oatmeal boxes for reference.
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While she was sending a large earthquake that had occurred off the coast of New Zealand, she noticed that some of its seismic waves had acted weird.
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They seemed to travel into the Earth's core before bouncing off of some kind of hard boundary.
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That didn't fit with the dominant idea of a gooey liquid core.
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So in 1936, Lehman published a paper theorizing that the Earth's center consisted of two parts, a liquid outer core surrounding a solid inner core.
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Lehman passed away in 1993 at the age of 104, core, living long enough to see her theory about the Earth's core become widely accepted scientific consensus.
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Lehman solved one huge mystery, but there's still so much to learn about Earth's core.
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Further seismological research confirmed the makeup of that inner core, iron and nickel.
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But a 2025 study of seismic waves showed
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that the core may be changing shape and even changing the direction and speed of its rotation.
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There's also evidence that the inner core isn't completely solid, but sort of squishy.
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And there may even be another layer, creatively named the innermost inner core.
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Like come on guys, Duane could do better than that.
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What?
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No, no shade Duane.
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Okay, so the core of our planet is a hot ball of iron and nickel.
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But it isn't just like chill in there.
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That ball of metal basically functions as Earth's bodyguard, using invisible armor to protect us.
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A magnetic field.
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The hot metal in the core's molten outer layer is constantly in motion, creating currents that generate a magnetic field surrounding the Earth.
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That field has two poles, north and south.
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Not to be confused with the geographic north and south poles.
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No penguins or Santa Claus here.
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Like in any other magnet, the magnetic field moves in a continuous loop, entering Earth at the north magnetic pole and leaving from the south magnetic pole.
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In space, the influence of Earth's magnetic field extends tens of thousands of kilometers around the planet, creating a bubble known as the Earth's magnetosphere.
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The magnetosphere is constantly moving and changing as it repels and traps charged particles from the sun and the rest of space, protecting Earth from radiation.
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The sun is constantly pushing energy into space in a flow of electrically charged plasma called solar wind.
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That solar wind helps shape our magnetosphere, compressing it on the sun-facing side
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and stretching it out in a tail behind the shaded side so that it wraps around the Earth.
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Without that magnetic field, the Earth wouldn't exist at all.
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Because it would be Mars.
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Let me explain.
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of years ago, the red planet may have had oceans, a thicker atmosphere, and its own magnetic field.
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But over time, Mars lost that magnetic field.
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And without it, solar wind and radiation stripped the planet of its atmosphere.
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No atmosphere, no water.
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Its oceans that may have once made it habitable were gone.
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If Earth's core didn't produce a magnetic field, we'd be in the same boat.
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So Earth's magnetosphere is pretty essential.
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But no matter how tough our planet's bodyguard is, It's not indestructible.
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In some cases, solar energy can cut through the core's defenses, especially when it's really volatile.
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See, the Sun's own magnetic field can get tangled up as it rotates, stretching and snapping, and then releasing energy in the form of solar storms.
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These could be massive explosions of light called solar flares, ejections of charged particles called radiation storms,
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or eruptions of plasma called coronal mass ejections.
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And these storms can cause major problems.
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Like in 1859, English astronomer Richard Carrington witnessed the biggest solar storm on record.
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A massive solar flare, followed by a series of coronal mass ejections, though he didn't know what they were at the time.
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The next day, the world was in chaos.
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Telegraph systems sparked, started fires, and wouldn't send messages.
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The New Orleans lights were suddenly visible as far south as Hawaii.
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And they were so bright in the northeastern U.S., people said they could read the newspaper in the middle of the night.
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They thought the world was ending, and you can't really blame them.
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But what actually happened was a geomagnetic storm.
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The solar storm's particles had disturbed the Earth's magnetosphere, and that disturbance interfered with technological and electrical systems across the world.
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Which brings us back to our Cold War mystery.
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That radio outage that spooked the U.S.?
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You guessed it.
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The culprit was really a geomagnetic storm, not an active war.
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Thankfully, the US Air Force's team of space weather forecasters informed
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the military leaders of increased solar activity before any fighter jets took off.
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History could have played out very differently.
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As for the world today, geomagnetic storms continue to happen once in a while.
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They can warm up the Earth's atmosphere, which increases drag on satellites, causing power outages and interrupting radio communication, GPS signals, airplanes, and spacecraft.
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Mass interruptions to internet connections, cell phones, and electricity can have huge consequences to just about everything that powers our modern lives.
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That can all feel like a lot to worry about, but the good news is we're not doomed, even if some movies make us think we are.
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Like, you might have heard that the Earth's magnetic field can change over time.
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Its poles can shift, or even completely reverse, and that's true.
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In the last 250 million years, Earth's magnetic poles have reversed hundreds of times.
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The last time they did was about 780,000 years ago, So it's probably time for another one.
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Movies and TV shows might have you worrying that a pole reversal would cause global destruction, leading us to a Mars-like future and a terrifying alien invasion.
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But magnetic pole reversal won't just happen overnight.
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Mathematical models suggest it could take thousands of years.
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And if it does, we might not even notice many changes.
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According to fossil records, sediment samples,
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and ice cores, previous magnetic field reversals haven't caused any major changes to Earth's climate or had a visible impact on life.
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It could affect the way migrating animals like sea turtles and birds navigate, but since that change would happen slowly, those animals would likely be able to adapt over time.
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The most that would happen might just be backwards compasses and confusing maps.
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Does that mean North Dakota would become South Dakota? So it turns out,
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it's kind of risky to live on a planet floating 93 million miles from a giant ball of fiery gas.
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But lucky for us, Earth's core provides us with the most powerful and visible armor imaginable.
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And while that armor can shift and change, that doesn't spell the end of the world, though it can wreak havoc from time to time.
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For now, space meteorologists are watching the skies for us and learning more every day.
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Next time, we'll learn all about minerals.
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See you then!
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Thanks for watching this episode of Crash Course Geology, which was filmed in our studio in Indianapolis, Indiana, and was made with the help of all these nice people.
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If you want to help keep Crash Course free for everyone forever, you can join our community on Patreon.
このレッスンについて
このレッスンでは、地球の中心についての興味深い情報を学びます。科学の進歩を追いながら、特にイングリット・レーマンの業績に焦点を当て、彼女の理論がどのように広く受け入れられたのかを探ります。このトピックは英語の事実やデータを学ぶだけでなく、科学的な議論の英語表現を練習する素晴らしい機会です。リスニングスキルを養い、発音を向上させるためのシャドーイングに適した内容です。
重要な語彙とフレーズ
- コア（core）: 地球の中心部分。
- 地震波（seismic waves）: 地震によって発生する波。
- 液体（liquid）: 状態を表す表現。
- 固体（solid）: 物質が形を持つことに関連する用語。
- 理論（theory）: 科学的な説明や推測のこと。
- 磁場（magnetic field）: 磁石の力が及ぶ空間。
- 回転（rotation）: 自転または回転運動に関連。
- 構成（makeup）: 物質の組成や構造。
練習のヒント
このビデオを使用して英語のスピーキングスキルを向上させるためには、以下のポイントを踏まえてシャドーイングを行うことをお勧めします。まず、ビデオをゆっくりと再生し、ナレーターのスピードを注意深く聞きましょう。各フレーズを聞き取り、正確に発音できるよう努めてください。特に、重要な語彙やフレーズの繰り返しが効果的です。
ナレーターのトーンやリズムを模倣することで、英語の発音を良くすることができます。時には一時停止し、自分の発音を声に出して確認してください。また、IELTS スピーキング対策にも役立つので、特に複雑な文を練習する際には、全体の流れを意識して練習しましょう。これにより、自然な会話ができるようになります。自信を持ってシャドーイングに取り組んでください！
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。