http://fr.wikipedia.org/wiki/Photosynth%C3%A8se
http://fr.wikipedia.org/wiki/Cycle_du_carbone
http://fr.wikipedia.org/wiki/Roche_carbon%C3%A9e
CO2 is not dissociated significantly by UV, no more than oxygen, epsilon in ozone at high altitude !!
The assertions of the 1970s were not commercial but serious based on the reserves known at the time, as currently where we are close to the peak, let's say !!
This is why we need a global view that puts things into perspective !!
The first elements thus produced, via the Calvin cycle, are sugars (glucose). This process is represented by the following equation:
6CO2 + 12H2O + light → C6H12O6 + 6O2 + 6H2O.
This equation is also often encountered in the form of a simple matter balance, which masks the fact that the atoms of the oxygen produced only come from water:
6CO2 + 6H2O + light → C6H12O6 + 6O2
One of the great scientific challenges is to calculate, with an acceptable approximation, the planetary carbon stocks and fluxes. They are measured in gigatonnes (Gt) or billion tonnes; the current estimates are (Gt of carbon):
* 750 Gt in the atmosphere;
* 38 Gt in the intermediate ocean (medium and deep), ie 100 times more than in the atmosphere;
* 3 Gt in soils;
* 610 Gt for flora and fauna.
As for the annual carbon exchanges (CO2) between the atmosphere and the Earth, most of them are natural:
* 60 Gt between vegetation and atmosphere;
* 90 Gt between the surface ocean and the atmosphere;
* 40 to 50 Gt between the surface ocean and marine life.
But humanity has added artificial flows to it:
* About 6 Gt due to the combustion of fossil fuels;
* 1 Gt approximately due to deforestation and forest fires.
The methane produced naturally hydrates on contact with water. If the cycle of this methane is still poorly understood, it is estimated that there would be 10 Gt of gas hydrates, including 000 to 10% of real gas (methane, ethane, propane, butane).
This quantity is twice as large as all the oil, coal and gas reserves combined: the quantity of methane thus trapped is 3000 times greater than that which is in the atmosphere.
Finally if carbon was not stored at all in the earth there would be no fossil fuel at all !!
1/1000 is a minimum (current peat which stores carbon in Siberia having burned a little this hot summer in Russia) and what limits it is the continental drift which recycles everything that is in the earth on 300 to 400 million years !!