We were taught is school that we are breathing in molecules from Caesar’s last breath, if this is true it should hold true for every person that ever lived, is our atmosphere really that fluid?

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We were taught is school that we are breathing in molecules from Caesar’s last breath, if this is true it should hold true for every person that ever lived, is our atmosphere really that fluid?

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This is true for every person that ever lived, and also for their every breath, not just the last one. Gases spread and mix very easily. One “breath” of air contains more than 10^22 molecules.

Well, every breath contains quintillions of molecules. The whole atmosphere has… I don’t even know, uncountably many molecules. Surely a couple of those quintillions of molecules in your breath will be blown somewhere far away. And then blown back later.

Yes, the atmosphere *is* that fluid, in the sense that the whole atmosphere acts as one big “pool”, it’s not really divided up into “pockets” anywhere, where “barriers” prevent air from traveling. Like in the broad scale yes, mountain ranges can block air fronts, but it’s not like they block *every single* molecule. And air molecules are very high-energy since they’re in a gaseous form. That means they move around a lot, just as a feature of their existence. Molecules in a liquid or solid form might stay put a little more often, but air molecules are flying everywhere in every direction all the time. Gas expands to fill the entirety of the container it’s in. Air goes up hundreds of miles into the sky, getting thinner and thinner yes but it’s only when you get to like thousands of miles up that the Earth’s gravity has basically prevented any significant number of air molecules from reaching.

Essentially. Matter cannot be created or destroyed so the atoms of oxygen now in our lungs have been on earth for all of geological history. The catch though is that chemical reaction can breakdown and combine molecules. So a water molecule that was once in Caesar’s bladder could have been broken down and eventually the oxygen atom, paired with another one (O2) can be in some scuba divers oxygen tank.

It could or could not be true. Breath contains oxygen, CO2, nitrogen, hydrogen. Processes on earth, inorganic or not, could absorb and trap these elements in the way they do. Plants absorb CO2 and capture the carbon to make cellulose to make their wood. Nitrogen could be captured by plants and put into the dirt, like clover does. These are a few examples. Is Augustus Caesar’s last breath floating around as a part of fluid air that can be inspired by you or me? Unknown. But those molecules that were in his lungs are most likely somewhere on earth? Yes.

There could be losses of air in space via shuttles and Space Station, etc. Oxygen oxidizes things, metals, iron oxide, rust that could fall to the ground and just sit there.

The atmosphere is pretty dynamic, lots of convection, so the time frame for total homogenization is on the order of years to decades. Some regions are better-mixed than others, but even trace contaminants end up in remote regions pretty quickly, as we have found with the distribution of trace contaminants like PCBs and tritium (the stuff gets everywhere in almost no time at all).

We take in about 1 gram of air with each breath. This compares to a total mass of something about 10^23 grams for the entire atmosphere (estimated at 5×10^19 kg, I just looked it up), so we breath in about 1/10^23 ths of the existing air. this is about the same as the number of atoms in a liter of air (which is about the same as a breath in volume) so the odds are pretty good that at least 1 atom (likely 10-100) also came out of Julius Caesar’s lungs on his last exhale, assuming a typical volume (not just a tiny gasp but even then, it only changes the odds by a factor or ten or so and we are in that range of uncertainty already with the estimates we are using).