Why do oxygen and nitrogen dominate the Earth's atmosphere?

Oxygen and nitrogen dominate the Earth's atmosphere due to natural processes like volcanic activity and biological activity.

The Earth's atmosphere is composed of roughly 78% nitrogen and 21% oxygen, with the remaining 1% consisting of other gases such as argon, carbon dioxide, and trace amounts of others. This composition is a result of various natural processes that have occurred over billions of years.

Nitrogen is the most abundant gas in the atmosphere. It is released into the atmosphere through volcanic activity and microbial processes in the soil. Nitrogen is a relatively inert gas, meaning it does not readily react with other elements. This property allows it to accumulate in the atmosphere over time. Additionally, nitrogen is continually recycled through the Earth's nitrogen cycle, where it is used and released by living organisms, further contributing to its abundance.

Oxygen, on the other hand, is primarily a product of photosynthesis, a process carried out by plants and certain types of bacteria. During photosynthesis, these organisms use sunlight to convert carbon dioxide and water into glucose and oxygen. The oxygen is then released into the atmosphere. Over billions of years, photosynthesising organisms have significantly increased the amount of oxygen in the atmosphere.

It's also worth noting that the Earth's gravitational field plays a role in maintaining the composition of the atmosphere. Lighter gases, such as hydrogen and helium, are more likely to escape the Earth's gravitational pull and be lost to space. In contrast, heavier gases like nitrogen and oxygen are more likely to be retained, contributing to their dominance in the atmosphere.

In conclusion, the dominance of oxygen and nitrogen in the Earth's atmosphere is a result of natural processes like volcanic activity, biological activity, and the Earth's gravitational field. These processes have led to the accumulation and retention of these gases over billions of years.