Fig. 3.

The hydrocarbon cycle. A schematic representation of the short-term hydrocarbon cycle, which occurs over days, and the long-term hydrocarbon cycle, which takes place over thousands to millions of years. A simplified process showing the conversion of CO₂ to alkanes using energy derived from photosynthesis is detailed in the enlarged cyanobacterial cell on the left. A simplified process showing the metabolism of alkanes is detailed in the enlarged hydrocarbon degrading bacterial cell on the right.