Nitrogen is an invisible, odorless gas that surrounds us constantly, making up the largest part of the air we breathe. It is a fundamental element, represented by the letter ‘N’ on the periodic table, and is involved in countless processes on Earth. While oxygen often gets the attention, nitrogen makes up the bulk of our atmosphere. Without it, life as we know it—from the smallest blade of grass to the largest animal—could not exist.
The Invisible Blanket: Nitrogen in the Air
Approximately 78% of the Earth’s atmosphere is composed of nitrogen gas, far more than the 21% that is oxygen. Nitrogen exists as a molecule where two atoms are bonded together very tightly, making it stable and mostly unreactive. It is colorless, tasteless, and odorless, which is why we do not notice it with every breath we take.
When you inhale, your lungs fill with a mix of gases, but your body only extracts and uses the oxygen. The nitrogen molecules travel into your lungs and leave unchanged when you exhale. In its gaseous form, nitrogen acts mostly as an inert background, preventing oxygen from reacting too quickly with other materials.
The Body’s Building Blocks
Although we do not use the gaseous nitrogen from the air, this element is necessary for all living things. Nitrogen is a core component of the molecules that build and operate every cell in your body. It is an ingredient in proteins, which are the construction materials for your muscles, hair, skin, and organs.
Proteins are large molecules made up of smaller units called amino acids, and nitrogen atoms form the backbone of these amino acids. Nitrogen is also a part of your DNA, which is the instruction manual for your body found inside every cell. DNA is made of units called nucleotides, and the nitrogen-containing parts of these units store the genetic code.
Plants depend on nitrogen to be healthy and green, using it to create chlorophyll, the molecule that captures sunlight to make food. Farmers often add nitrogen compounds as fertilizer to the soil to ensure crops grow strong. Animals, including humans, get the nitrogen they need by eating plants or other animals, passing the building blocks up the food chain.
The Great Recycling Story
The vast amount of nitrogen in the air is “locked up” and unusable by most life forms, so nature uses a recycling system called the nitrogen cycle. This cycle is a continuous journey that moves nitrogen from the atmosphere into the soil and living things, and then back into the air again. The first step involves breaking the strong bond of atmospheric nitrogen, a process called nitrogen fixation.
A small amount of nitrogen fixation happens naturally during a lightning strike, which provides enough energy to force nitrogen to combine with oxygen. Most of this unlocking work is done by special types of nitrogen-fixing bacteria, often found in the soil or living in the roots of plants like peas and beans. These bacteria convert the locked nitrogen gas into usable compounds like ammonia, which acts like a vitamin for the plants.
Once plants absorb these nitrogen compounds through their roots, the element moves into the food chain. Animals consume the plants, and the nitrogen becomes part of their proteins and DNA. When plants and animals die, or when animals produce waste, the nitrogen returns to the soil as organic matter.
Denitrification
Decomposer bacteria and fungi break down dead material, releasing the nitrogen back into the soil as simple compounds. A different group of bacteria then takes these soil compounds and converts them back into nitrogen gas, a process called denitrification. This step releases the nitrogen back into the atmosphere, completing the cycle.