What percentage of the atmosphere is oxygen?

Oxygen makes up approximately 21% of the Earth's atmosphere.

The Earth's atmosphere is a mixture of various gases, with nitrogen and oxygen being the most abundant. Oxygen, represented by the symbol O2, constitutes about 21% of the total volume. This percentage remains relatively constant in the lower atmosphere, where humans and other organisms live and breathe.

Oxygen is a vital element for life on Earth. It is essential for the process of respiration in most organisms, including humans. During respiration, oxygen is used to break down glucose and release energy, which is then used for various bodily functions. Without oxygen, this process would not be possible, and life as we know it would not exist.

The oxygen in our atmosphere is produced primarily through the process of photosynthesis carried out by plants, algae, and certain bacteria. During photosynthesis, these organisms use sunlight to convert carbon dioxide and water into glucose and oxygen. This oxygen is then released into the atmosphere, contributing to the 21% that we breathe.

It's also worth noting that while 21% may not seem like a lot, it's actually a carefully balanced amount. If the oxygen concentration were much higher, fires could easily get out of control because oxygen is a supporter of combustion. On the other hand, if the concentration were much lower, most organisms would not be able to survive due to lack of sufficient oxygen for respiration.

In summary, oxygen, making up about 21% of the Earth's atmosphere, plays a crucial role in supporting life on our planet. It is involved in key biological processes like respiration and photosynthesis, and its concentration in the atmosphere is maintained at a level that supports life while preventing excessive combustion.