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The carbon dioxide cycle
Carbon dioxide is the key metabolic gas of Gaia, influencing climate,
plant growth, and oxygen production. It cycles constantly through
the system from its source, volcanic output, to its final sink,
burial as limestone (calcium carbonate). The level of carbon dioxide
in the air, currently 0.03 per cent, depends on the balance between
the rates at which it leaks in and is pumped out. Plants by their
growth break up surface rocks and draw down carbon dioxide into
the soil. There, dissolved in rainwater, it reacts with basalt rocks
to form calcium bicarbonate, which is washed down to the sea and
used by the microscopic marine life to form shells. The ocean algae
also pump down carbon dioxide from the air. When the microflora
die, their shells rain down to the ocean floor, to form sediments
of limestone and chalk.
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