Carbon Cycle

The carbon cycle is the way the element carbon moves between living things, the air, the oceans, and the rocks of Earth. Carbon is one of the most important elements for life. Every plant, animal, and person on Earth is built partly out of carbon. The same carbon atoms get used over and over again, passing from one place to another in a giant loop that never stops.

Carbon is stored in four main places. It sits in the air as a gas called carbon dioxide. It is locked inside living things, like trees and animals. It is dissolved in the oceans. And it is buried deep underground in rocks, coal, oil, and natural gas.

Plants pull carbon out of the air. During photosynthesis, a plant takes in carbon dioxide through tiny holes in its leaves. It uses sunlight to turn that carbon into sugar and new plant parts. When an animal eats the plant, the carbon moves into the animal's body. When the animal breathes out, some of that carbon goes back into the air as carbon dioxide. This part of the cycle can happen in just a few hours.

Other parts of the cycle take much longer. When a plant or animal dies, its body breaks down. Bacteria and fungi release some of the carbon back into the air. But sometimes dead plants and animals get buried before they fully rot. Squeezed under layers of rock for millions of years, they slowly turn into coal, oil, and natural gas. These are called fossil fuels because they are made from ancient life.

The oceans also play a huge role. Seawater soaks up carbon dioxide from the air. Tiny ocean creatures use that carbon to build shells. When they die, their shells sink and pile up on the sea floor. Over millions of years, the shells become limestone rock. Some of the limestone you see on a cliff today was once tiny sea animals.

People are changing the carbon cycle. When we burn fossil fuels to power cars, homes, and factories, we release carbon that was buried for 300 million years, from a time long before dinosaurs. That extra carbon dioxide builds up in the air faster than plants and oceans can absorb it. Scientists agree this is the main reason Earth is warming. Understanding the carbon cycle is how we figure out where all that extra carbon goes, and what to do about it.