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  • Planet Earth is the home of every lifeform,

  • known to us, in the universe.

  • Its age is about 1/3 of the age of the universe

  • and, admitted,

  • It is a thing of beauty.

  • a slightly squashed fair with a heavy metal core,

  • and a lighter surface crust,

  • wrapped in a thin sliver of sweet air to breathe,

  • with vast oceans,

  • fertile plains,

  • magnificent mountains,

  • fresh water rivers, streams, lakes and aquifers,

  • orbiting a star which warms us,

  • and gives us energy.

  • But how did our home come in to existence,

  • and what's it made of?

  • 4.6 billion years ago,

  • Earth was created from the remnants of dead stars,

  • that collected in a giant, dirty gas cloud.

  • The gas cloud became denser in its center,

  • and formed an accretion disk.

  • small particles started clumping together,

  • and building larger and larger objects,

  • until they form the objects we call "Planets" today.

  • This process took 10 to 20 million years,

  • and is still not very well understood.

  • At about this time, when the solar system was young and chaotic,

  • a giant object, about as big as Mars,

  • collided with our home.

  • The impact was violent,

  • and if the object had been more massive,

  • it might have destroyed Earth.

  • Materials from Earth were smashed out into orbit,

  • and formed the Moon,

  • which is the biggest satellite in relation to its planet in the solar system.

  • At this time, Earth was a hot hell,

  • constantly being hit by asteroids,

  • with seas of lava,

  • and a toxic atmosphere.

  • But something was about to change drastically.

  • Earth cooled down.

  • Water from the inside of the Earth

  • wandered to the surface and rained down on Earth,

  • only to vaporize again and become clouds.

  • Millions of asteroids brought more and more water to our planet.

  • All the water on Earth has about this volume compared to Earth.

  • Today,

  • the surface of Earth is 71% water,

  • and 29% land.

  • 97.5% is saline water,

  • while only 2.5% is fresh water.

  • The Fresh water is 69% ice and snow,

  • 30% are ground waters,

  • and only about 1% make up the remaining ground waters.

  • But even this small part is mostly frozen.

  • Only a tiny part of our water is actually lakes and rivers.

  • and an even tinier part is bound in living things.

  • So, gradually the Earth cooled down,

  • and the surface formed a thin crust.

  • But inside the earth, hot rock continue to swirl about,

  • moving the crust from below and breaking it apart.

  • This process is called "Plate Tectonics",

  • and is happening right now.

  • We'll make a whole video about it in the future.

  • For now,

  • let's just say that the crust of Earth consisted of

  • separate giant plates that move around.

  • As they meet, they crumble, and create mighty mountains.

  • OR:

  • violently plunge back down, deeper into Earth,

  • creating deep trenches.

  • That's the way the highest place on Earth was formed: Mt.Everest,

  • and the deepest: the Mariana Trench.

  • From our perspective,

  • Earth's mountains and trenches are mighty indeed,

  • but when you look at the Earth in cross-section,

  • you can see how tiny they actually are.

  • The part we stand on is the crust,

  • which is about 50 kilometers thick,

  • though it can vary between 5 and 70 kilometers

  • By the way,

  • the deepest hole ever drilled by man

  • is 12.262 kilometers deep.

  • After the crust, comes the mantle.

  • It's a silicate rocky shell,

  • and about 2,900 kilometers thick.

  • The mantle consists of the upper mantle, and the lower mantle.

  • The upper mantle has different regions, too.

  • It's upper part, which is viscous and carries the crust,

  • is called the "Lithosphere."

  • After that, there comes the "Asthenosphere,"

  • which consists of less mobile, mostly solid material.

  • The lower mantle reaches deep down to the outer core of Earth.

  • Earth's outer core is a liquid layer of iron and nickel,

  • about 2,266 kilometers thick.

  • Temperatures vary from 4,000℃(7,232℉)

  • to 5,700℃(10,292℉).

  • And in the center, is the inner core.

  • It's mostly solid,

  • a ball made of an iron-nickel alloy.

  • with a radius of about 1,200 kilometers.

  • 70% of the size of the moon,

  • and about the temperature of the surface of the Sun.

  • It is slowly growing

  • at an estimated rate of about 1mm/year.

  • Now, for some respective,

  • this small layer of crystallized melt products of former molten mantle,

  • is where we live.

  • Then, there's Earth's magnetic field.

  • It's an invisible phenomenon

  • that diverts high energy particles coming from the Sun and other sources,

  • allowing for a stable environment

  • with comparatively little radiation impact on Earth.

  • But why is it there?

  • Actually, we don't really know a terrible lot about that.

  • We know, it has something to do with the core of Earth.

  • Inside this metal sphere,

  • large electrical currents flow in complicated patterns.

  • They cause a magnetic field,

  • that sort of stabilizes itself according to the laws of electrodynamics.

  • This entire system is called the "Dynamo."

  • But, don't let us fool you into thinking we have it all figured out.

  • Speaking of breathtaking information,

  • what about the airy stuff that surrounds us?

  • By volume,

  • dry air consists mostly of Nitrogen,

  • Oxygen,

  • Argon,

  • Carbon,

  • a variable amount of water vapor,

  • and small amounts of other gases.

  • Humans are very dependent on the lowest layer of the atmosphere:

  • the Troposphere - Where the weather is.

  • It's 12 kilometers thick on average.

  • Above that is the Stratosphere,

  • which is where the ozone layer protects us

  • from the sun's most aggressive type of light.

  • Above that is the Mesosphere - the coolest place on Earth,

  • with an average temperature around -85℃(-121℉).

  • At about 80 kilometers up, the Thermosphere starts.

  • The transition to space is a fluent one, without clear borders.

  • but humans decided that space starts here.

  • At about 100 kilometers, Earth stops, and space begins,

  • though the atmosphere extends a bit further.

  • In this region, we find the Ionosphere,

  • the aurora borealis,

  • and the ISS,

  • and the outermost layer is the Exosphere,

  • stretching up to 10,000 kilometers.

  • It merges fluently with outer space,

  • where there's no atmosphere at all.

  • The atoms and molecules in this area are so far apart,

  • that they can travel hundreds of kilometers

  • without colliding with each other.

  • OK.

  • Humans, in their present form,

  • have only been around for 200,000 years.

  • - that's 0.004% of Earth's history.

  • Not long, really.

  • And, here we are now,

  • living in a thin, moist layer on a small, wet rock.

  • We call this rock: Earth.

  • It is the product of the universe's deepest workings,

  • the result of a constant process of creation and destruction,

  • happening all of the universe, all the time,

  • helped by chance,

  • the laws of the universe and random events,

  • we are really lucky.

Planet Earth is the home of every lifeform,

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地球について知っておくべきすべてのこと (Everything You Need to Know About Planet Earth)

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    Eating に公開 2021 年 01 月 14 日
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