Nitrogen
The nitrogen cycle is an important cycle to the atmosphere. Nitrogen is an essential part of the biological molecules such as proteins and nucleic acid, which makes nitrogen essential for all living organisms. Nitrogen makes up 78 percent of the atmosphere. There are five steps in the nitrogen cycle between the abiotic environment and the organisms: nitrogen fixation, nitrification, assimilation, ammonification, and dentrification. Nitrogen fixation is the conversion of gaseous nitrogen to ammonia. This process is carried out my nitrogen-fixing bacteria in soil and aquatic environments.