How do reef-building corals and Mollusca contribute to the carbon cycle, and how can their hard parts become fossilized?

How does the combustion of biomass and fossil fuels produce carbon dioxide?

How did partially decomposed organic matter from past eras contribute to the formation of coal, oil, and natural gas?

Under what conditions does peat form, and why is organic matter only partially decomposed in these conditions?

What happens to methane in the atmosphere, and how is it transformed into carbon dioxide and water?

How and where is methane produced from organic matter, and what role do methanogenic archaeans play in this process?

How is carbon dioxide produced by respiration, and what happens to it after it is released by organisms?

How does carbon dioxide enter autotrophs from the atmosphere or water?

In what forms is carbon present in aquatic ecosystems, and how does it differ from atmospheric carbon?

How do autotrophs convert carbon dioxide into carbohydrates and other carbon compounds?