Hypoxia and Medicine

Why is there less oxygene in high altitudes?

I'm doing a 3 minute oral on "Why there is less oxygen in high altitudes" and I need to find some explanations. The one I found is that gravity is weaker up there and so gases, including oxygen, are more dispersed thus we have a hard time breathing when climbing high mountains etc. Now I need 1 or 2 more explanations to make my 3 minutes on stage. Thx.

Public Comments

1. i believe its because oxygen and all the other gasses in the air have a weight. so they are affected just like every thing else with a weight. a good way to explain it might be to say the oxygen weighs more then the vacuum of space much like water is heavyer then air and water will be more attracted to the earth pushing the air up.
2. It is important to remember that the concentration of oxygen is the same both on the surface and up at altitude, approximately 21%. The thing that changes is the pressure. If you think of a column of air that stretches from the surface to 100,000 feet, the Earth's gravity is pulling all of the air towards its center. The air near the ground has the weight of all of the air above it pushing down on it. As you go higher, there is less air above it pushing down on it. Force = mass × acceleration. The acceleration is due to gravity and roughly constant. Thus, as you move up in altitude and there is less mass above you, the force goes down. Pressure = force × area. Since the force is going down, the pressure is going down too. The key to why it is harder to breath is because the pressure is lower. With a lower pressure, there is less driving force to get the air through the membranes and into your lungs.