All life is based on carbon .
Yet by weight, carbon is not one of the most abundant elements within the Earth's crust. Estimated major stores of carbon on the Earth. 540 to 610 Fossil Fuel Deposits 4000 Ecosystems gain most of their carbon dioxide from the atmosphere . A number of autotrophic organisms have specialized mechanisms that allow for absorption of this gas into their cells. With the addition of water and energy from solar radiation , these organisms use photosynthesis to chemically convert the carbon dioxide to carbon-based sugar molecules.