Caption: "This carbon cycle diagram shows the storage and annual exchange of carbon between the atmosphere, hydrosphere and geosphere in gigatons---or billions of tons---of Carbon (GtC). Burning fossil fuels by people adds about 5.5 GtC of carbon per year into the atmosphere."
Carbon in plants mostly comes from the air---and animals get their carbon from plants.
Image link: Wikipedia: File:Carbon cycle-cute diagram.svg.
Local file: local link: carbon_cycle.html.
File: Earth atmosphere file: carbon_cycle.html.