What would happen if earth had no nitrogen?

The air pressure would decrease enormously, as nitrogen makes up more than three quarters of the air we breath. So without it, there would be substantially less air! Life cycles in themselves would fall apart, as even at the most basic level nitrogen is used. It is present in DNA, urine, gases, almost everything living has nitrogen in it. Seeing as the air would now mostly comprise of oxygen and carbon dioxide, lots of animals and living creatures would die because of the incredibly high concentrations of these gases. Plants require Nitrogen to carry out photo synthesis (so no O2) and ammonia required nitrogen to made in the harbor process(one of the most frequently used chemicals in industry). you also need nitrogen to create DNA and there's not really any life without DNA or RNA (found in bacteria). Nitrogen also stop the air being explodable... if O2 filled the earths atmosphere you only need one person with a lighter to set the world aflame :) there are hundreds of other reasons why we need nitrogen please add more.

Breathing pure (100%) oxygen can kill us, and we need nitrogen when we breathe in oxygen. Nitrogen combines with oxygen and that is what we breathe in.

Also, ammonia wouldn't have existed