SPACE STRAW

Hey, Vsauce. Michael here. Our atmosphere is a thin veil of air, held to earth's surface by gravity. We live in it, we breathe it, we walk through it every day; it contains all weather, but yet it is almost nothing. In fact, 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.

And because our atmosphere gets thinner exponentially as you go up, 90 percent of our atmosphere's mass at this scale could fit within a space as thin as just a third of an apple's skin. But that shrimpy sliver of a peel would still be thousands of times thicker than you are tall. We humans are itsy bitsy dots strolling around in a skinny sky. But that skinny sky does a lot.

Think about this. What if I had a really awesome big straw, and I stuck one end in the ocean and the other end out in space? Would outer space be able to suck all the water out? We know that in the naked, exposed veneer vacuum of space, all non-concealed gases in your body would be violently farted and burped out. Sucked out. But sucking is not attractive.

Instead, sucking merely refers to a flow from a region of higher pressure to a region of lower pressure. In other words, a vacuum cleaner in and of itself does not attract matter to itself. Like I said in my video with no title, if you were to turn on a vacuum cleaner at sea level, a region inside the cleaner becomes as thin as air in Denver, Colorado. External air, which is at a greater pressure, is then literally pushed by its own greater pressure into the machine, bringing dust and debris with it.

The point is, 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. That amount of force can only push pure water up about 10.3 meters, or 33.9 feet.

Because outer space is not 10 meters up, it's more like 100,000 meters up. A space straw would be a terrible doomsday device for a supervillain to use to get rid of our oceans. Our atmosphere just isn't heavy or strong enough to push water into orbit. Because the weight of air above, pushing molecules below in all directions, is responsible for air pressure, air lowered down exerts more pressure.

The air at your feet pushes with a slightly greater force than the air at your head. Now, across the human body, you can't tell the difference. But if an object is light enough, it can be affected by this difference, which is why a helium balloon floats. The air down here pushes a tiny bit more strongly than the air up here, and since the balloon is lighter than the same volume of air, it's literally pushed up by the air more strongly than gravity pulls it down.

This upward force, caused by a surrounding fluid or gas that counteracts an object's weight, is known as buoyancy. Now, here on the surface of the earth, the buoyancy of air isn't enough to cause humans to float away or be lifted. But it exists. In fact, in a perfect vacuum, you would weigh about a fifth of a pound more than you do right now. Thanks, air!

Back to our balloon friend. He's not going to float up forever in outer space, escaping earth. Eventually, as the atmosphere thins out, and the balloon expands, it will pop and fall back down to earth, its helium spreading throughout the atmosphere.

So, besides rockets that we intentionally launch off of Earth, does our atmosphere ever lose anything? Does earth ever lose anything? Does earth ever gain anything? I mean, I used to be smaller; I used to be a little kid. But all of the atoms and molecules in my body right now simply came from things that I consumed.

Things that I ate, or drank, or breathed in. When new kids are born, the earth doesn't get heavier, because a new baby is just a rearrangement of atoms and molecules that used to be inside its mother or molecules that she ate, drank, or breathed in, all of which came from earth. Everything's recycled, so is the earth not gaining or losing mass?

Well, to begin, 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, which is why, as I've said before, we are likely to one day run out of helium. Pretty soon.

But the earth gains mass in some ways as well. For instance, every year it's been estimated that 10 to 20 million kilograms of space dust and meteorite fragments fall to Earth, making it heavier. Now, if you factor in the energy that the earth radiates away, which is equivalent to mass, as well as the energy the earth gets from the Sun and holds onto, for instance, using its greenhouse gases, in total it has been calculated that every year earth becomes 50 million kilograms lighter.

That might sound like a lot, but it is only 0.00000000000000001 percent of Earth's total mass, which means that for all intents and purposes, the stuff that we are made of, the atoms and molecules in our bodies, 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.

Remember that six trillion kilograms of oxygen that all humans inhale every year? Well, each and every one of us, individually contributes by breathing about 8.5 million times per year. Here's the thing about a breath. Because molecules are so frustratingly small, a single little breath contains about 10 sextillion molecules.

In a poetic twist of symmetry, Earth's entire atmosphere contains a volume of air equal to about 10 sextillion breaths. The number of molecules in one breath is equal to the number of breaths our earth has to give us, that is assuming, of course, that we never exhaled anything and it never got renewed, which it does.

And because our atmosphere gets circulated so quickly and because we breathe so often and because molecules are so small, statistically speaking, our atmosphere, our skinny little peel of air, is crowded with molecules that we've all had inside our bodies and been breathing.

To make this really mind-blowing, let's 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. And carbon dioxide is useful to plants, which absorb it and then turn it into sugars. It doesn't just inertly float around our atmosphere forever.

Okay. Well, it has been estimated that it takes one breath about one year to thoroughly mix throughout the hemispheres of earth and about ten years to thoroughly mix within the troposphere that we live in and the stratosphere above. Now, given that only 5 percent of what we exhale is carbon dioxide and only 20 percent 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.

A few of them may have been molecules that you used five years ago to remember where you left your keys. A few of them may have been inside your brain when you first fell in love. And a few of them, almost certainly, were inside the brain of your mother while she was giving birth to you.

So, take a deep breath because our air is crowded with history. And keep breathing, because within the next ten years it is certain that I will breathe in a few carbon dioxide molecules that are inside your brain right now as you listen to me say that.

As always, thanks for watching.