What would happen if all the atmospheric nitrogen was replaced with another inert gas?

Answer 1

What a curious question!

If all the atmospheric nitrogen gas was replaced with another inert gas we'd be in a lot of trouble. Many important biologically active molecules contain nitrogen. Without the inert nitrogen in the air, the organisms that use atmospheric nitrogen and fix it into forms that other organisms can use would die off. This death would cause a ripple effect moving up the food chain until eventually humans were unable to get the nitrogen they need for proteins and other important biological molecules. So to answer your question directly it would mean the end of the world as we know it.

Great Question!