Phosphorus is a chemical element that can glow in the dark and can burst into flame when exposed to air. Scientists discovered it accidentally in 1669 when a German alchemist was boiling urine, trying to turn ordinary materials into gold. Instead, he created a waxy substance that glowed eerily in his dark laboratory.

Pure phosphorus is so reactive that it must be stored underwater or in sealed containers. White phosphorus, one form, is extremely dangerous because it can ignite spontaneously at room temperature. Red phosphorus, a safer form, is used on the striking surface of matchboxes: when you scrape a match across it, the friction creates enough heat to ignite the match head.

Your body contains a lot of phosphorus, mostly in your bones and teeth, making it essential for life. Every cell in your body uses phosphorus to store and transfer energy. Plants need phosphorus to grow, which is why farmers add phosphate fertilizers to their fields.

Today, phosphorus appears in fireworks, fertilizers, and some other products. Despite being discovered while someone was experimenting with pee, phosphorus turned out to be one of the most important elements for life on Earth.