This is a video by Vsauce's Michael Aranda where he discusses the Earth's atmosphere and its properties. He starts by explaining that the atmosphere is a thin layer of air holding Earth's surface to the planet by gravity. It's what we breathe and walk through every day, containing all weather phenomena. If Earth were the size of an apple, the atmosphere would only be as thick as the apple's skin. The atmosphere gets thinner exponentially as you go up, and 90% of its mass could fit within a space as thin as just a third of an apple's skin.
Aranda then compares the Earth's atmosphere to a vacuum cleaner or a space straw. He explains that a vacuum cleaner or a space straw can only push air up about ten meters due to the atmospheric pressure at sea level. The same force can't push water into orbit because the weight of the air above pushing molecules below in all directions is responsible for air pressure. The air at your feet pushes with a slightly greater force than the air at your head, but if an object is light enough, it can be affected by this difference. This is why a helium balloon floats up.
Aranda also mentions that the Earth does lose some stuff like hydrogen and helium due to its gravity, which eventually fly out into space or get picked off by solar wind at the edge of our atmosphere. However, the Earth gains mass in some ways, for instance, every year, it's estimated that 10 to 20 million kilograms of space dust and meteorite fragments fall to Earth, making it heavier.
In conclusion, Aranda explains that the Earth's atmosphere is crowded with molecules from our bodies. Every breath contains at least a few molecules that were once inside our brains, and it's mathematically certain that every breath we take contains at least a few molecules that were once inside your brain.
1. The speaker is discussing the Earth's atmosphere, which is a thin veil of air held to Earth's surface by gravity. The atmosphere contains all weather but is almost nothing in fact.
2. If the Earth was the size of an apple, our atmosphere from the ground all the way to outer space would only be about as thick as the skin of an apple.
3. The atmosphere gets thinner exponentially as you go up. 90% of our atmosphere's mass at this scale could fit within a space as thin as just a third of an apple's skin.
4. The strength of the force pushing air into a vacuum cleaner can only be as strong as the pressure of the surrounding air. Here on Earth, using a vacuum cleaner or even a space straw, that pressure is atmospheric pressure at sea level, about 15 pounds per square inch or 65.4 Newtons.
5. The buoyancy of air isn't enough to cause humans to float away or be lifted, but it exists. In a perfect vacuum, you would weigh about a fifth of a pound more than you do right now.
6. Earth does lose some stuff for instance, hydrogen and helium are a bit too light to stick around because of Earth's gravity. They eventually fly out into space or get picked off by solar wind at the edge of our atmosphere.
7. Earth gains mass in some ways as well. Every year, it's been estimated that 10 to 20 million kilograms of space dust and meteorite fragments fall to earth, making it heavier.
8. For all intents and purposes, the stuff that we are made of, the food that we eat, the water that we drink, our best friends, has all been here since the early days of Earth, including the air that you are breathing right now.
9. If we focus only on carbon dioxide, we don't just breathe it in and then right back out again. It's a waste product that comes from all over our bodies. Carbon dioxide is useful to plants, which absorb it and then turn it into sugars.
10. It has been estimated that it takes one breath about one year to thoroughly mix throughout the hemispheres of Earth and about 10 years to thoroughly mix within the troposphere that we live in and the stratosphere above.
11. Given that only 5% of what we exhale is carbon dioxide and only 20% of that came from metabolism within our brain, even if we assume that 99.99999 percent of all the CO2 you have ever exhaled has been trapped in the oceans or absorbed by plants and made into sugars, it is still mathematically certain even if you were in a brand new place you've never breathed in before that every breath you take contains at least a few molecules that were once inside your brain.