Carbohydrates, a common source of energy for humans, are organic compounds composed only of carbon, hydrogen, and oxygen. Proteins and fats also contain carbon, meaning everything we ingest to fuel our bodies contains carbon in some form. Interestingly enough, fossil fuels all contain carbons as well, which means everything we use to fuel our vehicles uses carbon as well (even in the case of electric cars, that electricity used to charge the car may be generated at a plant through burning hydrocarbons).