Calcium is a chemical element that forms the main building block of bones and teeth. Your skeleton contains about two pounds of calcium, which gives bones their hardness and strength. Without enough calcium, bones become weak and brittle, like chalk that crumbles easily instead of sturdy wood.

You get calcium by eating foods like milk, cheese, yogurt, and leafy green vegetables. Your body constantly uses calcium for building bones, helping muscles contract, making your heart beat, and allowing nerves to send signals throughout your body.

Calcium appears throughout nature beyond just living things. Seashells, coral reefs, limestone rocks, and even chalk are all made largely of calcium compounds. The White Cliffs of Dover in England contain massive amounts of calcium from ancient sea creatures whose shells accumulated over millions of years.

Scientists use the symbol Ca for calcium on the periodic table, and it's one of the most abundant elements in Earth's crust.