Depending on what you mean by form.
Previously non-existent C atoms are formed:
1> It is formed in stars as one of the fusion reactions that fuel the star. (stellar nucleosynthesis.)
2> It (C-14) is formed in the upper atmosphere by the interaction of cosmic rays and N-14.
Carbon previously combined with other elements:
3> It (coal) is formed by the decomposition of dead organisms.
4> It can be formed by the incomplete combustion of a fuel, such as a candle or firewood. The soot lin the fireplace and chimney is carbon.
Look up the carbon cycle.
An overview:
It exists in the atmosphere as CO2, the oceans as carbonates, and rocks lithosphere) as carbonates and fossil fuels, as well as the biosphere as a variety of biological compounds, and the man-made world as plastics, etc.
Previously non-existent C atoms are formed:
1> It is formed in stars as one of the fusion reactions that fuel the star. (stellar nucleosynthesis.)
2> It (C-14) is formed in the upper atmosphere by the interaction of cosmic rays and N-14.
Carbon previously combined with other elements:
3> It (coal) is formed by the decomposition of dead organisms.
4> It can be formed by the incomplete combustion of a fuel, such as a candle or firewood. The soot lin the fireplace and chimney is carbon.
Look up the carbon cycle.
An overview:
It exists in the atmosphere as CO2, the oceans as carbonates, and rocks lithosphere) as carbonates and fossil fuels, as well as the biosphere as a variety of biological compounds, and the man-made world as plastics, etc.
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try that:
http://en.wikipedia.org/wiki/Carbon
http://en.wikipedia.org/wiki/Carbon