Carbon and the Carbon Cycle

To understand the carbon cycle there are five big things you need know about carbon.

1. Carbon is present in all living things.

flowerYou are 18.5% carbon. Your cells and DNA contain carbon. All plants and animals contain carbon. Carbon is often called the building block of life. That's because all living things contain carbon.

2. The amount of carbon on earth doesn't change.

There is always the same amount of carbon on earth. What changes is where it can be found and what other atoms it is joined with. A few places carbon can be found are:

cliffs and trees along canal
There's carbon everywhere: in rocks, trees, water, and air.
  • underground in oil, natural gas, and certain types of rocks,
  • in plants and animals, and
  • in the atmosphere as carbon dioxide gas (CO2).

Carbon might move into the atmosphere when we burn gasoline but the total amount on earth will stay the same.

3. Where carbon is found can change.

The total amount of carbon doesn't change on earth—just where it is located. For example, if you take oil from underground and burn it you'll get carbon dioxide gas (CO2). You just moved carbon from the ground into the atmosphere.

If a plant uses CO2 in the atmosphere to grow, the carbon has moved from the atmosphere to the plant. If the plant catches on fire, the CO2 might go back into the atmosphere.

It is likely some carbon atoms will have been in many places since the earth was formed.

4. Carbon can be bonded to different atoms at different times in the carbon cycle.

If you had pure carbon (C) and oxygen gas (O2) you could end up with carbon dioxide gas (CO2).
C + O2 -> CO2

Plants could take the CO2, and through a series of chemical reactions called photosynthesis, change it into oxygen gas (O2) and sugar (glucose is C6H12O6) or other compounds.

In both examples the amount of carbon stayed the same but was transformed into different substances.

5. There are many different chemical compounds that contain carbon.

Carbon dioxide (CO2) Natural gas (CH4) Chalk (CaCO3)
Carbohydrates (like sugars and starches) Amino acids that make up proteins and DNA

Carbon compounds are so important that chemistry and biology majors in college usually take two courses just on the compounds carbon forms.

How is burning like breathing? Read about Candles, Oxygen Gas, and Carbon Dioxide Gas.