Nitrogen compounds in the soil are broken down by Pseudomonas bacteria through a process called denitrification, thereby returning nitrogen in its original form to the atmosphere. The weathering of rocks by wind, rain and friction also releases the free nitrogen present within them into the air.
Nitrogen makes up nearly 80 percent of the Earth's atmosphere, moving in various forms from the air to plants and animals, then to the soil and back into the air through the nitrogen cycle. Denitrification is one part of this cycle, where Pseudomonas bacteria inhale nitrogen compounds from swampy oxygen-free soil, and exhale free nitrogen into the atmosphere. This, along with weathering, restores nature's nitrogen balance.