Nitrogen is a colorless, odorless gas that makes up about 78% of the air you breathe. Every time you take a breath, most of what enters your lungs is nitrogen, though your body actually uses the oxygen mixed in with it.

Nitrogen is an element, one of the basic building blocks that everything in the universe is made from. Plants need nitrogen to grow, which is why farmers add fertilizers containing nitrogen to their soil. Without enough nitrogen, crops produce smaller harvests and plants turn yellow. Animals, including humans, need nitrogen too: it's a key ingredient in proteins, which build our muscles, skin, and organs.

The challenge is that while nitrogen gas surrounds us, plants and animals can't use it directly from the air. It must first be converted into other forms, like ammonia or nitrates. This happens naturally through lightning strikes and certain bacteria in soil, but scientists have also learned to convert nitrogen industrially, which revolutionized farming in the 20th century.

Nitrogen also has practical uses beyond biology. Because it doesn't react easily with other substances, liquid nitrogen (which is extremely cold at about minus 320 degrees Fahrenheit) is used to freeze things quickly, preserve biological samples, and create special effects like the fog you might see at science demonstrations.