What is the major constituent of the atmosphere today?

The major constituent of the atmosphere today is nitrogen, which makes up approximately 78% of the Earth's atmosphere by volume. Its abundance is a key factor in maintaining atmospheric pressure and supporting life processes. Nitrogen is relatively inert and plays a crucial role in the nitrogen cycle, which is vital for living organisms as it forms an essential component of amino acids, proteins, and nucleic acids.

In contrast, oxygen, while critical for the respiration of most living organisms, constitutes about 21% of the atmosphere. Although it's essential for life, it is not the most abundant gas. Argon, a noble gas, comprises about 0.93% of the atmosphere and does not participate actively in most chemical reactions. Carbon monoxide is present in trace amounts and is primarily produced from incomplete combustion, posing health risks rather than forming a major component of the atmosphere. Thus, nitrogen's predominance is a fundamental aspect of atmospheric composition, influencing various environmental and biological processes.