How Did Earth and the Solar System Form?발음듣기
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How Did Earth and the Solar System Form?
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100% 한국어
번역 5명 참여
출처 : 칸아카데미
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That's because in a Universe with a hundred elements, you haven't just got a hundred different materials.발음듣기
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Those elements can combine with each other in a huge number of different ways to form millions and millions of new materials, all the materials we see in the world around us.발음듣기
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All these new materials eventually combine to find... to create entirely new astronomical bodies.발음듣기
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But before we describe how the Earth and the other planets of the solar system was created, there's a little problem we have to take up.발음듣기
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You remember from the last unit, we saw that all those new elements that were created made up only two percent of all the atoms in the Universe.발음듣기
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Yet, if we look at our earth, we'll find that 90% of the earth is made up of elements like iron, oxygen, silicon, magnesium, and other elements created in supernova and dying stars.발음듣기
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Now, before I give my answer, I'd like to ask if you have any ideas about how that might have happened.발음듣기
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And chemistry is all about how different elements link up, how the atoms link up to form what we call molecules.발음듣기
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Some elements such as helium are very, very stable, they hardly ever link up with other atoms.발음듣기
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Hydrogen and oxygen, for example, are always looking for chances to link up with other atoms.발음듣기
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If you see burning or you see a flame, what you're really seeing is oxygen linking up really violently with other atoms, it's very reactive indeed.발음듣기
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Each molecule has its own distinctive qualities, which may be very different from the elements of which they're formed.발음듣기
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For example, hydrogen and oxygen are both gases, but when they combine, they form a very, very familiar liquid - water, H2O.발음듣기
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Now, in a diamond the bonds are extremely strong and extremely rigid, so a diamond is very tough indeed.발음듣기
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But carbon atoms could also link up with themselves to form a very different material, graphite.발음듣기
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Now, these different types of links, different types of bonds mean we have a huge variety of different types of materials.발음듣기
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But note that it's mostly elements other than hydrogen or helium that make up these chemicals,발음듣기
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and that's one reason why when we talk about rich chemistry, we're talking mostly about that tiny two percent of elements from the periodic table.발음듣기
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Atoms began to form molecules even in deep space, in the... in the clouds of matter ejected by supernovae and dying stars.발음듣기
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And we know there's water, plenty of ice, carbon dioxide, ammonia, acetic acid, a whole range of simple molecules that are very familiar in daily life.발음듣기
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Silicates are molecules made from silicon and oxygen, and they make up most of the rocks in the earth's crust.발음듣기
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Now, in space, these molecules, which were pretty simple by the way, they included 10 to 20 atoms, at most 60.발음듣기
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but around newly born stars, it turns out you could do a huge amount of interesting stuff with these molecules.발음듣기
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To see how this works, what we're going to do is we're going to travel back in time 4.5 billion years, and we're gonna zoom in.발음듣기
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We're gonna zoom in on one tiny part of it, and we're gonna look at the birth of our solar system.발음듣기
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Now, our sun formed like any other star, from the collapse of a cloud of matter under the pressure of gravity.발음듣기
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That collapse like many others was probably triggered by a huge supernova explosion somewhere in our region of the Milky Way,발음듣기
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and that supernova explosion also seeded this cloud with lots of new materials from other supernovae and from dying stars.발음듣기
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Now, this is something that happens throughout the Universe, which is why the Universe is full of flat disks from the Milky Way itself to our solar system, even to the rings around Saturn.발음듣기
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Now, as the proplyd that eventually formed our solar system began to collapse, at its center, it got hotter and hotter and hotter, until eventually fusion began and our sun was born.발음듣기
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All that stuff was orbiting around the sun and, amazingly, that tiny residue is what formed all the rest of the solar system.발음듣기
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The intense heat of the young sun drove away gassy materials from the inner parts of the solar system, and above all, it drove away a lot of hydrogen and helium, leaving that as a region deprived of hydrogen and helium.발음듣기
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And all that gassy material gathered further out in the solar system and eventually condense to form the gassy giants.발음듣기
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So, what we're left with is a tiny residue of a tiny residue to form the inner rocky planets, including our Earth.발음듣기
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Closer to the sun, from that tiny residue of a residue, you find material orbiting, orbiting in the inner orbits, and that material is less gassy.발음듣기
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You have little dust motes that eventually will gather together through electrostatic forces or collisions to form little rocks.발음듣기
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And in each orbit, you eventually get large objects that finally sweep up through their gravitational pull, everything else that's in the orbit.발음듣기
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And if you want to be persuaded how violent it was, get out a pair of binoculars and look at the moon one night and look at those craters.발음듣기
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Our moon was probably created when an object perhaps the size of Mars collided with our earth, our young earth and it gouged out a huge chunk of the earth,발음듣기
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and that stuff orbited around the Earth and slowly accreted to form the object that we call the moon.발음듣기
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So in this way, through these processes, over about ten to 20 million years, our solar system formed.발음듣기
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And we end up with a solar system that has inner rocky planets in the inner orbits, these large gassy planets in the outer orbits and woven through them, lots of space debris.발음듣기
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And strangely what that does is it rather increases the chances that out there somewhere, there is life of some form.발음듣기
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So exciting is the science by the way that I even have an app on my phone that tells me all about the most recent discoveries of so-called exoplanets, which is what planets around other stars are called.발음듣기
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First, we saw that chemistry links chemicals to form simple molecules, a whole range of new materials are floating through space.발음듣기
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And secondly, we saw that in the environments, or we can call them the Goldilocks environments around newly formed stars,발음듣기
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those molecules get smashed together, they get brought together by chemistry and by gravity and by electricity to form objects like dust motes, meteorites, asteroids and eventually, planets and solar systems.발음듣기
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And that's because planets, and in particular, rocky planets like our Earth, are significantly more complex than stars.발음듣기
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They are more complex because they have more internal structure, but they are also much more complex chemically.발음듣기
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Okay. Now, I've worn this lab coat throughout the whole lecture even though I'm a historian.발음듣기
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