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Opens up more questions than it answers. It seems when trees die, they become earth or even oil. How come they don't completely dissolve into air again? And if they don't completely dissolve into air, how come all the CO2 is not bound in the earth yet (trees pluck it out of the air, then die and bind it to the ground)? There would have to be bacteria or something that converts soil into air (CO2), but then, why don't they dissolve everything?

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Trees do dissolve. Forest fires are the most elegant way -- the reaction liberates much of the carbon and all of the oxygen into gasses including CO2, and the cycle is complete.

Bacteria that break down the rotting remains of a dead tree also consume the energy stored in the cellulose and release gasses like carbon dioxide and methane. At some point the remains don't contain bonds with easily freed energy and you have regular old dirt. If they had a way to break down the dirt further they would, but the cost is too high.

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