Carbon is a chemical element that forms the foundation of all living things on Earth. Every plant, animal, and person contains carbon as part of their basic structure. When you look at a tree, pet a dog, or see your own reflection, you're looking at something built largely from carbon atoms.

Carbon has a special ability that makes life possible: it can link up with other atoms in countless different ways, forming everything from the sugar in an apple to the proteins in your muscles. Scientists sometimes call Earth “the carbon planet” because this element plays such a central role in life here.

You encounter carbon in many forms. The graphite in your pencil is pure carbon, and so is diamond, one of the hardest natural substances on Earth. Both are made of exactly the same element, just arranged differently at the atomic level. When wood or paper burns, the black ash left behind is mostly carbon. The carbon dioxide you exhale with every breath contains carbon combined with oxygen.

In recent decades, the term “carbon” has become shorthand for carbon dioxide and other carbon-containing gases in the atmosphere. When people talk about “reducing carbon emissions” or a “carbon footprint,” they mean the amount of these gases released into the air, which affects Earth's climate. Your carbon footprint measures how much carbon dioxide your activities produce, from heating your home to the transportation you use.