Following Carbon Around Earth

By the end of this lesson, you will be able to describe the carbon cycle and explain how carbon moves between the air, living things, water, and rocks.

Carbon is an element found in every living thing, in the air, in the ocean, and deep underground. The carbon cycle is the continuous movement of carbon atoms among these places. Carbon never gets used up or destroyed. It just changes form and location, over and over, sometimes in days and sometimes over millions of years.

Picture a pecan tree in a Texas front yard. The tree pulls carbon dioxide, a gas made of carbon and oxygen, out of the air and uses sunlight to build leaves, wood, and pecans through photosynthesis, the process plants use to make food from sunlight, water, and carbon dioxide. When a squirrel eats a pecan, that carbon moves into the squirrel's body. When the squirrel breathes out, some carbon returns to the air as carbon dioxide. When leaves fall and rot, decomposers like bacteria and fungi break them down and release carbon back into the soil and air.

Some carbon takes a much slower path. Ocean water absorbs carbon dioxide from the air, and sea creatures use it to build shells that later become limestone rock. Ancient buried plants and sea life turned into coal, oil, and natural gas over millions of years. That is why we call them fossil fuels.

Human activity speeds part of this cycle up. When people burn fossil fuels in cars, power plants, and factories, carbon that was locked underground for millions of years enters the air in just seconds. Cutting down forests also means fewer trees are pulling carbon dioxide out of the air. Extra carbon dioxide in the atmosphere traps more heat, which can change global climate.

Try it: if you exhale right now, name two places that carbon could travel to next.