Picture a scenario where all 7 billion people suddenly “poof” off the planet, clothes and all, and the globe is suddenly devoid of people. (This is basically the premise behind the series Life After People). Would there suddenly be less air in the world? My thinking is that, the instant people vanish, there are 7 billion people-sized holes in the atmosphere, and the existing air rushes in to fill the hole (something like Archimedes’ famous bathtub discovery, in reverse). Would the loss of that much oxygen to fill the holes that were once occupied by people be significant enough for the life that is left on earth? Would it even occur?
I don’t follow your thinking. Why would air moving from being next to a human, to being in the place the human was, reduce the amount of air? It’s not disappearing, just moving a few centimetres.
it’s not oxygen or any part of the air that will disappear but rather solid people made largely of carbon-based solids, calcium and water. the water loss will probably be insignificant but the carbohydrates and proteins would be lost to the usual carbon cycle. it’ll be almost the same as losing all of one year’s crop harvest and livestock processing for one year.
Obviously there would be exactly the same amount of oxygen in the atmosphere, and indeed, exactly the same amount of atmosphere, as there was before. You have not ‘poofed’ any atmosphere away in your scenario.
Apart from that, the volume of all the human bodies in the world compared to the total mass of the atmosphere is tiny, so direct and immediate effects would be insignificant. With all those people no longer breathing in oxygen and breathing out CO2 (and all their industry and power production soon grinding to a halt too) maybe you would see a brief, very tiny rise in oxygen levels (and concomitant drop in CO2) but I am sure other types of animal would soon multiply enough to cancel out any effect from just the people disappearing. Also, there would probably be some big fires. I guess, after that had blown over, the end of industry would solve the global warming problem though (unless it is already too late).
The only actual air that is in human bodies is pretty much found in the lungs. Sure, there’s more oxygen in the blood and all that, but that isn’t really in gas form anymore. Going with the idea that I randomly found online that the average human male’s lung capacity is 6 L, that means that as an upper bound, the lung capacity of humanity is 4.2 × 10[SUP]10[/SUP] L, or 4.2 × 10[SUP]7[/SUP] m[SUP]3[/SUP]. At sea level, air has a density of 1.294 kg/m[SUP]3[/SUP], and humanity’s lung capacity is thus about 5.43 × 10[SUP]7[/SUP] kg. The total mass of the atmosphere is 5 × 10[SUP]18[/SUP] kg. So, if humanity were to disappear, it would take 0.0000000011% of the planet’s air with it. I don’t think that it would be possible to notice this.
The only actual air that is in human bodies is pretty much found in the lungs. Sure, there’s more oxygen in the blood and all that, but that isn’t really in gas form anymore. Going with the idea that I randomly found online that the average human male’s lung capacity is 6 L, that means that as an upper bound, the lung capacity of humanity is 4.2 × 10[SUP]10[/SUP] L, or 4.2 × 10[SUP]7[/SUP] m[SUP]3[/SUP]. At sea level, air has a density of 1.294 kg/m[SUP]3[/SUP], and humanity’s lung capacity is thus about 5.43 × 10[SUP]7[/SUP] kg. The total mass of the atmosphere is 5 × 10[SUP]18[/SUP] kg. So, if humanity were to vanish without a trace, it would take 0.0000000011% of the planet’s air with it. I don’t think that it would be possible to notice this.
Wasn’t really asking about the CO2 we contribute to the environment but more like: if you take a human out of a bathtub filled with water, there’s less water in the tub, ecause the human displaced the water. I thought our just being there displaced the air around us, creating less air, but yeah, never realized that it’d be a miniscue amount.
(And fires, end of industry, etc., are all things explored in the Life After People series. Fascinating watch if you can get your eyes on it.)
The volume of water doesn’t change. The displacement merely increases the relative level of the water in the container. Otherwise, where would the extra water come from when you add a solid object to its container?
No, there isn’t. The level goes down, but there’s exactly the same amount of water.
Exactly - the human displaced (moved) water when they got in, and undid that when they got out. Net change - none, aside from the tiny amount left clinging to that person’s skin.
Even by your own thinking, if humans disappearing made air vanish then when those same humans got created and grew air would have been created, so net change - none.
Nonsense.
Do you honestly think that humans consume their entire yearly food intake in one day? If not then how the hell could the instantaneous loss of human biomass be even remotely equivalent to the annual food consumption?
7 billion people, let’s say average 150lb each (that may be a high average). That’s 900 billion pounds of long pork, let’s make it an even trillion, or about half a trillion kilos of long pork.
That’s the equivalent of half a trillion litres of long pork puree, assuming a density of a human about that of water. (See hands waving like crazy during this math…)
0.5x10^12 L = 5x10^14 cc of lpp (long pork puree).
The earth is about 6.4x10^4km radius, or 6.4x10^10cm. Surface of sphere is 4 x pi x r^2; area of earth in cm is about 8.0 x10^21 cm^2 if my math is still up to high school level, which it never was.
Dividing out, if all the people on earth were puree’ed and spread evenly all over the landscape with a giant butter knife of doom, they would form a layer 1.6x10^-6 cm thick across the globe.
So logically, if all the humans on the earth disappeared, the overall atmosphere would shrink by 2 millionths of a centimeter. The air pressure at sea level afterward would be about the same as what it is now at 2 millionths of a centimeter above sea level.
Basically, humans body-wise are not that big a proportion of the world area or mass. The obesity epidemic may change that… 
Oops. 6.4x10^4km is 6.4x10^9 cm (See, these metric thing are confusing. I was thinking mm).
So the area would be 8x10^19, LPP layer would be 1.6x10^-4cm; the layer might even be visible as a thin red smear.
Alternatively, 7B people (7x10^9), 8x10^19cm^2 of earth surface, means each person gets 1.1x10^10cm^2 of surface, or 1.1x10^6 m^2. A million square meters per person; that’s a square kilometer per person. Even if we eliminate sea surface, that’s a quarter of a square kilometer per person. A recent article on the 7 billion population mentioned that with decent breathing room, 360m people could stand on Manhattan; the whole earth population easily stands on 21 Manhattans. Look at a globe, that’s a pretty tiny area over all.
And do you think your mass is equivalent to the amount of food you eat in one day? :dubious:
That said, a quick and dirty estimate. Let the average human being consist of 150 pounds of meat. Let the calorie content of meat be 100 kCal/oz. Then the average human being contains 240,000 kCal or about 120 days’ worth of food. So human biomass is about one third of a year’s worth of food production/consumption.
This is the math, done Wolfram Alpha style.
Interestingly, your 7 billion humans pureed would neatly contained in a cubic (leak-proof, I hope) box 1/2 mile on each side.
We wouldn’t even fill up Sidney Harbor.
In the grand scheme of things, that’s not a lot.
“Displacing” means “moving somewhere else”. It doesn’t mean “creating” or “destroying”. When you get in the bath, you move the water out of the way, so it rises higher up the tub. You’re not creating any extra water (or if you are, you ought to get out first and use the receptacle provided 
). When you get out, you’re not destroying any water, just allowing it to settle back at its lower level.
Similarly, if you took all the people out of the atmosphere, there wouldn’t be any less air, but it would be able to settle just a little bit lower. The depth of the atmosphere would be less, by a tiny, tiny, tiny amount (I’m sure someone could do the maths, but it would likely be of the order of millimetres) that for all practical purposes would be unmeasurable.
The closest analogy I can think of, using your bathtub example, is to put a few handfuls of sand at the bottom of a big swimming pool and then fill it with water. Now remove the sand (using a filter so you only remove the sand, not any water).
Has the level of water in the pool dropped? Yes, but not measurably. Is there less water in the pool? No.
I’m getting hungry.
I don’t know how how to do the math, but a puree, as used here, sounds more it would be placed in a [URL=“http://www.auravita.com/product/Stainless-Steel-Terrine-Mould.DEBU10787.html”]terrine mould]((human volume) * 7 billion - Wolfram|Alpha), and after preparation could be spread on crackers as a canapé for some alien landing party. (For the mold cited, assume that the base is flat, without the silly heart indent.)
A meat puree is also the base of liverwursts.
For both of these preparations, I wonder how long the containers would be.
(Balogna and Mortadella are extra credit.)
More importantly, water is non-compressible, but air IS compressible. When all the human vanish in this scenario, the molecules move in to the empty spaces, and are now ever so slightly farther apart than they were before. The outer boundary of Earth’s atmosphere won’t go down in the same manner as the bathtub example. Instead, the density of the air will be slightly thinner. (Not on a perceptible or even measurable level, of course.)
What if the ensuing puree was allowed to sun-dry or dehydrate prior to being stuffed into the box?