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Hydrocarbons

For more than half a billion years, photosynthesis has made life possible on Earth. Plants absorb solar energy and use it to convert carbon dioxide and water into oxygen and carbohydrates such as sugar, starch and cellulose. These carbohydrates and other organic materials eventually settle on the ground and in stream, lake and sea beds.

As these organic materials become more deeply buried, heat and pressure transform them into solid, liquid or gaseous hydrocarbons known as fossil fuels - coal, crude oil or natural gas. Coal is generally formed from the remains of terrestrial (land-based) plants. Oil is typically derived from marine (water-based) plants and animals, mainly algae that have been gently "cooked" for at least one million years at a temperature between 50° and 150° Celsius. Natural gas can be formed from almost any marine or terrestrial organic materials, under a wide variety of temperatures and pressures.