conflagration of forests. This mechanism, however, would not raise oxygen levels if they became too low. If plants can be shown to robustly over-produce O2 then perhaps only the high oxygen forest fires regulator is necessary. Recent work on the findings of fire-caused charcoal in Carboniferous and Cretaceous coal measures, in geologic periods when O2 did exceed 25%, has supported Lovelock's contention. Processing of CO2 Gaia scientists see the participation of living organisms in the carbon cycle as one of the complex processes that maintain conditions suitable for life. The only significant natural source of atmospheric carbon dioxide (CO2) is volcanic activity, while the only significant removal is through the precipitation of carbonate rocks. Carbon precipitation, solution and fixation are influenced by the bacteria and plant roots in soils, where they improve gaseous circulation, or in coral reefs, where calcium carbonate is deposited as a solid on the sea floor. Calcium carbonate is used by living organisms to manufacture carbonaceous tests and shells. Once dead, the living organisms' shells fall. Some arrive at the bottom of the oceans where plate tectonics and heat and/or pressure eventually convert them to deposits of chalk and limestone. Much of the falling dead shells, however, re-dissolve into the ocean below the carbon compensation depth. One of these organisms is Emiliania huxleyi, an abundant coccolithophore algae which may have a role in the formation of clouds. CO2 excess is compensated by an increase of coccolithophorid life, increasing the amount of CO2 locked in the ocean floor. Coccolithophorids, if the CLAW Hypothesis turns out to be supported (see "Regulation of Global Surface Temperature" above), could help increase the cloud cover, hence control the surface temperature, help cool the whole planet and favor precipitation necessary for terrestrial plants. Lately the atmospheric CO2 concentration has increased and there is some evidence that concentrations of ocean algal blooms are also increasing. Lichen and other organisms accelerate the weathering of rocks in the surface, while the decomposition of rocks also happens faster in the soil, thanks to the activity of roots, fungi, bacteria and subterranean animals. The flow of carbon dioxide from the atmosphere to the soil is therefore regulated with the help of living beings. When CO2 levels rise in the atmosphere the temperature increases and plants grow. This growth brings higher consumption of CO2 by the plants, who process it into the soil, removing it from the atmosphere.