The nitrogen cycle describes the transformation of nitrogen in nature. Nitrogen makes up 78% of the atmosphere but needs to be converted to usable forms for organisms. Bacteria fix nitrogen gas into ammonia through nitrogenase enzymes. Ammonia is further converted through nitrification, denitrification, and ammonification to move between nitrogen's many oxidation states. These processes are essential to life but also leave the nitrogen budget of the ocean unbalanced, with excess nitrogen escaping to the atmosphere through denitrification.