Alright, this may seem a bit of a childish question, but for my sake I need it answered. So please stay with me. Alright, pretty much what this is all about is the effect that space exploration has on the Earth's air supply. We were all sitting around talking about the creation of a space station and having it in orbit. The thought struck me that for people to live on the space station (whether that be the intention of it or not) they would need to have a decent supply of air that was re-manufactured via machine instead of plant. Then I took that and said that if enough space stations were created then eventually the amount of Oxygen on the earth would become so depleted that humans could no longer exist on it. Yes, I realize that the earth has quite an abundant supply of oxygen. It is in water, carbon dioxide, carbon monoxide, etc. The list goes on and on. I'm sure there are other supplies of oxygen as well, but eventually we would disperse them to so many different places, the air on the earth itself would become noticeably thinner. Yes I realize that this will never happen, and the amount of space stations that would need to be created is vast, and our limit on other resources might become a factor before that. All that aside, the amount of air on the earth would thin out because a gas naturally fills its entire container. And if you take away some of the air, the air will thin out to compensate for what you took out. Correct? Another way of saying this is to describe all of the Earth's oxygen supply as 100 units (this includes the oxygen in the air, water, and everything else on Earth). Lets say we take 10 units of the earth's oxygen and put it in a gigantic space station orbiting around the Earth. If this were to take place, then those 10 units of air would no longer be on Earth, and the 90 units of oxygen on earth would spread out and fill up the space of the removed oxygen, therefore making it thinner. If this were to happen numerous times, the amount of oxygen on Earth would thin out to such an extent, then it could not My entire hall does not agree with this, and it seems that they think that the Earth will magically supply us with more oxygen. Some of their debates are photosynthesis, and claim that the plants will reproduce our air supply, which absolutely makes no sense to me, because I've clearly stated to them numerous times that CO2 has oxygen in it, and they are just separating the C from the 2 O, and that the O must be there in the first place. Yes, I realize this is a stupid question, but it seems that my entire floor is against me here, and I would just like some knowledgeable reasons as to why this is true, or not true. Basically, I'm trying to figure out who's thought pattern is flawed here. Thank you for your time.