Carbon

Carbon is a chemical element found in every living thing on Earth. An element is a basic kind of matter that cannot be broken down into anything simpler. Carbon's symbol on the periodic table is the letter C. Its atoms are small and have six protons in the center. Scientists sometimes call carbon "the element of life" because it is the main building block of plants, animals, and people.

Carbon is special because its atoms can link up with other atoms in many ways. A single carbon atom can connect to four other atoms at once. This lets carbon build long chains, rings, and branching shapes. No other element is quite as good at making complicated molecules. That is why carbon shows up in so many different substances, from sugar to gasoline to your own DNA.

Pure carbon comes in a few surprising forms. Diamond is one form. The atoms are packed tightly in a strong crystal, which is why diamond is the hardest natural material we know. Graphite is another form. Its atoms are arranged in flat sheets that slide off easily, which is why it leaves a mark when you drag a pencil across paper. Soot, coal, and charcoal are also mostly carbon. Same element, very different stuff.

Your body is about 18 percent carbon by weight. The proteins in your muscles, the fats in your food, and the sugars your body burns for energy all contain carbon. Plants pull carbon out of the air to grow. They take in a gas called carbon dioxide and use sunlight to turn it into leaves, stems, and fruit. When you eat a plant, or eat an animal that ate a plant, that carbon becomes part of you.

Carbon keeps moving between the air, the oceans, living things, and the ground. Scientists call this the carbon cycle. Coal, oil, and natural gas are the buried remains of ancient plants and tiny sea creatures, which means they are mostly carbon too. Burning these fuels for energy releases their carbon back into the air as carbon dioxide. That extra carbon dioxide traps heat and is warming the planet, which is why carbon is at the center of discussions about climate change.

There is even a way to date old things using carbon. A special kind of carbon, called carbon-14, slowly breaks down over thousands of years. By measuring how much is left in an old bone or piece of wood, scientists can tell how long ago it was alive.