00:00Planet Earth is the home of every life form known to us in the universe.
00:05Its age is about a third of the age of the universe and, admit it, it is a thing of beauty.
00:11A slightly squashed sphere with a heavy metal core and a lighter surface crust
00:16wrapped in a thin sliver of sweet air to breathe, with vast oceans, fertile plains,
00:21magnificent mountains, freshwater rivers, streams, lakes and aquifers,
00:26orbiting a star which warms us and gives us energy.
00:30But how did our home come into existence and what's it made of?
00:364.6 billion years ago, Earth was created from the remnants of dead stars
00:40that collected in a giant dirty gas cloud.
00:43The gas cloud became denser in its center and formed an accretion disk.
00:48Small particles started clumping together and building larger and larger objects
00:52until they formed the objects we call planets today.
00:56This process took 10 to 20 million years and is still not very well understood.
01:01At about this time, when the solar system was young and chaotic,
01:04a giant object about as big as Mars collided with our home.
01:08The impact was violent and if the object had been more massive, it might have destroyed Earth.
01:14Material from Earth was smashed out into orbit and formed the Moon,
01:18which is the biggest satellite in relation to its planet in the solar system.
01:22At this time, Earth was a hot hell, constantly being hit by asteroids,
01:27with seas of lava and a toxic atmosphere.
01:30But something was about to change drastically.
01:33Earth cooled down.
01:35Water from the inside of the Earth wandered to the surface and rained down on Earth,
01:39only to vaporize again and become clouds.
01:42Millions of asteroids brought more and more water to our planet.
01:47All the water on Earth has about this volume compared to Earth.
01:51Today, the surface of Earth is 71% water and 29% land.
01:5697.5% is saline water, while only 2.5% is freshwater.
02:02The freshwater is 69% ice and snow, 30% are groundwaters,
02:07and only about 1% make up the remaining groundwaters.
02:11But even this small part is mostly frozen.
02:14Only a tiny part of our water is actually lakes and rivers,
02:18and an even tinier part is bound in living things.
02:22So, gradually the Earth cooled down and the surface formed a thin crust.
02:26But inside the Earth, hot rock continued to swirl about,
02:30moving the crust from below and breaking it apart.
02:33This process is called plate tectonics and is happening right now.
02:38We'll make a whole video about it in the future.
02:40For now, let's just say that the crust of Earth consists of separate giant plates that move around.
02:45As they meet, they crumble and create mighty mountains,
02:48or violently plunge back down deeper into Earth, creating deep trenches.
02:53That's the way the highest place on Earth was formed, Mount Everest,
02:57and the deepest, the Mariana Trench.
02:59From our perspective, Earth's mountains and trenches are mighty indeed,
03:04but when you look at the Earth in cross-section, you can see how tiny they actually are.
03:08The part we stand on is the crust, which is about 50 km thick,
03:12though it can vary between 5 and 70 km.
03:15By the way, the deepest hole ever drilled by man is 12.262 km deep.
03:20After the crust comes the mantle.
03:22It's a silicate rocky shell and about 2,900 km thick.
03:27The mantle consists of the upper mantle and the lower mantle.
03:30The upper mantle has different regions too.
03:33Its upper part, which is viscous and carries the crust, is called the lithosphere.
03:38After that, there comes the asthenosphere, which consists of less mobile, mostly solid material.
03:44The lower mantle reaches deep down to the outer core of Earth.
03:48Earth's outer core is a liquid layer of iron and nickel about 2,266 km thick.
03:54Temperatures vary from 4,000 °C to 5,700 °C.
04:00And in the centre is the inner core.
04:03It's mostly solid, a ball made of an iron-nickel alloy, with a radius of about 1,200 km,
04:0970% the size of the Moon and about the temperature of the surface of the Sun.
04:14It is slowly growing at an estimated rate of about 1 mm per year.
04:19Now for some perspective.
04:21This small layer of crystallized milk products of former molten mantle is where we live.
04:27Then there's Earth's magnetic field.
04:30It's an invisible phenomenon that diverts high-energy particles coming from the Sun and other sources,
04:35allowing for a stable environment with comparatively little radiation impact on Earth.
04:40But why is it there?
04:42Actually, we don't really know a terrible lot about that.
04:45We know it has something to do with the core of the Earth.
04:48Inside this metal sphere, large electrical currents flow in complicated patterns.
04:53They cause a magnetic field that sort of stabilizes itself according to the laws of electrodynamics.
04:59This entire system is called the dynamo.
05:02But don't let us fool you into thinking we have it all figured out.
05:06Speaking of breathtaking information, what about the airy stuff that surrounds us?
05:12By volume, dry air consists mostly of nitrogen, oxygen, argon, carbon,
05:18a variable amount of water vapour and small amounts of other gases.
05:22Humans are very dependent on the lowest layer of the atmosphere, the troposphere, where the weather is.
05:28It's 12 kilometres thick on average.
05:31Above that is the stratosphere, which is where the ozone layer protects us from the Sun's most aggressive type of light.
05:37Above that is the mesosphere, the coolest place on Earth, with an average temperature around minus 85 degrees Celsius.
05:45At about 80 kilometres up, the thermosphere starts.
05:48The transition to space is a fluent one without clear borders, but humans decided that space starts here.
05:55At about 100 kilometres, Earth stops and space begins, though the atmosphere extends a bit further.
06:01In this region, we find the ionosphere, the aurora borealis and the ISS.
06:07And the outermost layer is the exosphere, stretching up to 10,000 kilometres.
06:12It merges fluently with outer space, where there's no atmosphere at all.
06:17The atoms and molecules in this area are so far apart that they can travel hundreds of kilometres without colliding with each other.
06:24Okay, humans in their present form have only been around for 200,000 years.
06:29That's 0.004% of Earth's history.
06:33Not long, really.
06:35And here we are now, living in a thin, moist layer on a small, wet rock.
06:40We call this rock Earth.
06:42It is the product of the Universe's deepest workings, the result of a constant process of creation and destruction,
06:49happening all over the Universe all the time, helped by chance, the laws of the Universe and random events.
06:56We are really lucky.
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