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 mount 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.
