Recycling Carbon

As science-fiction writers often remind us, life on Earth is based on carbon. The element is found in everything from proteins and carbohydrates to DNA — everything that makes it possible for life to move, eat, and reproduce.

Yet carbon isn’t something that we ingest directly — you can’t order a plate of charcoal at your favorite food trailer. Instead, carbon comes to us through plants and tiny plant-like organisms in the oceans, which get it from carbon dioxide in the atmosphere.

Plants live through a process called photosynthesis. Chlorophyll — the compound that makes plants look green — absorbs sunlight, providing energy. This energy powers chemical reactions that break down carbon dioxide into its two components, carbon and oxygen. These elements are then combined with others to make sugars and more complex organic compounds, such as proteins, fats, and carbohydrates. Some of the oxygen produced by these reactions is released into the air.

Fish, birds, and other animals — including people — then eat the plants, or they eat animals than have eaten them. They use oxygen to break down the carbon-based compounds to provide food and energy. This process also makes carbon dioxide and water, which the animals release back into the environment. That provides the compounds that plants need — keeping the cycle of life going.

So we owe our existence to plants, which convert the carbon dioxide in the atmosphere to other compounds that sustain the carbon-based life on our planet.