|
The cycle of life - the entire biosphere here on earth - is essentially a closed system. And the Laws of Physics say that NO energy or material can be created or destroyed.
So, the weathering process and other processes that have sunk carbon underground over millions of years, have removed it from the cycle.
Plants split water, and release the oxygen, and use the hydrogen along with carbon dioxide from the air to grow. When the plant dies, OR if it is eaten, the same amount of carbon eventually makes it's way back into the air. And the oxygen is breathed in by animals, and use it with the carbon in our food to grow. We breathe out carbon dioxide, that is then used by plants.
The long term balance of the system is neutral - unless humans pull carbon out of the ground, and burn it. Volcanoes also release carbon, but it is carbon 13, so we can measure how much that is.
Burning plants releases mostly carbon 12, with a known proportion of carbon 14 - the radioactive isotope of carbon. (Carbon 14 is how we do carbon dating.)
Burning fossil fuel releases ONLY carbon 12 - because it is older than 50,000 years (which is the total time it takes for carbon 14 to decay). This is one of the reasons we know that the additional carbon dioxide in the air is from fossil fuels.
|