That totally depends on your definition of life. The short answer: None.
The long answer: Millions of years ago the planet Earth had little oxygen to speak of, and anerobic bacteria (those that didn't breathe oxygen) was the dominant form of life. Then came along what's known as "The Great Oxygenation", in which Earth's atmosphere started becoming more oxygen-based. Once oxygen did appear, the oxygen breathers typically outdeveloped and outbreeded other forms of life, which if I recall correctly has something to do with oxygen being far more efficient for certain biological processes than other elements such as methane.
So it's not that life actually needs oxygen to survive, it's just that oxygen is far more efficient for certain biological processes -- when it's actually available. This does not answer the question. The answer is 18% oxygen at sea level. Source: PADI's Enriched Air Divers Manual
I presume the question is specifically asked about human beings other than about all living things. A healthy person requires to have the oxygen saturation (SpO2) of arterial blood at a minimum level of 92 % to breathe comfortably. If the oxygen saturation drops down to a level lower than 92%, the person will suffer short breath or breathing difficulty when he moves or works. However, if the person remains stationary or inactive, he or she may not feel any significant discomfort at all even when the oxygen saturation level drops down to below 80% although he or she may feel tired and sleepy.
Of course all humans need oxygen in order to survive, it is the main source for breathing. The lowest percentage needed for survival is 16-17%.
oxygen takes up 20 % of the air we breathe
Suprisingly not all humans need oxygen to survive. Some seem to wander around for years brain dead, but still functional. It's a mystery.
For a short time I guess.
17%
44
we breath in oxygen and plants breath co2
About 20%% of the air we breath is oxygen. The PaO2 (oxygen breathed in mmhg) is approximately 100 mmhg.
carbon dioxideNo.We breath in oxygen and breath out Carbon dioxcide.Now plants on the other hand, take in our waste, carbon dioxcide, and let out what we need, oxygen. thats why you may find the air fresher in a forest!
At the top of Mount Everest, the percentage of oxygen in the air is the same as that at sea level (about 21% oxygen). However, atmospheric pressure decreases as altitude increases, and the atmospheric pressure at the summit of Everest is 33% that of sea level.Therefore, there is 66% less oxygen than there is at sea level.
Nope -- they do just exactly the opposite: inhale and use oxygen, and exhale more carbon dioxide, just as all mammals do. This was an old wive's tale that's been around for years, that goes on to say cats can suck away a baby's breath -- which has no basis in fact whatsoever.
20%
100%. All of the oxygen that I breathe comes from the air! The answer that you were probably after, but did not ask, was about the percentage of oxygen in the air that we breathe. The questions may sound similar but they are not the same. The answer is a little over 20%.
You breathe out 16.3% oxygen.
Yes. All humans breath a type of air called oxygen. Without oxygen we would die.
We get Oxygen from atmosphere.It is in air we breath.
oxygen
Approximately 21% of the air we breath is oxygen.
we breath in oxygen and plants breath co2
If we didn't Breath Air how else would we get our Oxygen!??
They get the oxygen from the air they breath.
when you breath in throught the nose all of that oxygen from the air comes from the oxygen and carbon dioxide that other people breath in.
We get rid of waste when we breath out and when we breath in we take oxygen in to our lungs and breath.