- Please sort and annotate in a user-friendly manner and consider archiving the URLs behind the links you provide. See also related web sources.
- Earth & its Atmosphere From the website of Carnegie Mellon University Office of Technology for Education Collaboration Server.
- The Nitrogen Cycle From a website page of the National Aeronautics and Space Administration (NASA)
- The Nitrogen Cycle John Arthur Harrison. From the website of Visionlearning, an educational resource for faculty and student, funded by the National Science Foundation (NSF).