eli5, why is there less oxygen at higher altitudes?

Question

eli5, why is there less oxygen at higher altitudes?

In: 2

Answer 1

Air has mass (weight) and unlike liquids, air is compressible, meaning you can squeeze more of it into a smaller area.

So all of the air around the planet is just stacked on top of other air, and all that weight compresses the bottom layers to make it more dense.

There’s quite literally more air at sea level than there is at 10,000 feet because of this compression. If you filled a jar with sea level air, and another with 10,000 feet air, despite being the same size, and containing the same thing, the sea level jar would weight slightly more because there’s more air squeezed into that space.

So, following that same logic, there’s more oxygen at sea level because there’s more air.