12,000
because its hard to breathe thin air above earths surface, the higher you go its hard to breathe oxygen.
I think that you may have left out a zero.I live at 3700 feet and breathe quite well.If it was 30,000 then it would be hard to breathe because at Mount Everest the air is thin. Gravity holds the air next to the ground and it begins to be thin on top of that very high mountain. So, think of air as a liquid that rests on the earth. It is only so thick ad then there is none in space.
At 20,000 feet above sea level, the air is thin and lacks sufficient oxygen for normal breathing. Without supplemental oxygen, it becomes difficult to breathe at this altitude.
Thin air, such as at high altitudes, can make it harder to breathe because it contains less oxygen. This can lead to shortness of breath, fatigue, and dizziness. In contrast, thick air, which may be humid or polluted, can also be difficult to breathe but for different reasons.
Actually frogs dont breathe from their lungs. They have lungs but they don't use them because their skin is so thin that they can breathe from it.
Because the higher you go in altitude, the harder it is 2 breathe because of thin air.
You run out of breathe easily because the air is more thin
The atmosphere becomes too thin to breathe at high elevations, typically above 8,000 feet (2,400 meters) above sea level.
There is sufficient oxygenated air in the lower half of the troposphere, the lowest level of the atmosphere. Above 10,000 feet ASL (3 km) the air begins to become thin, and by 25,000 feet (8 km), it can barely provide enough oxygen for human activities.
Because the air is thin
Your diaphragm helps you breathe the air you need every day.
288 cubic feet of "air" or 19 cubic feet of pure oxygen .