Carbon dioxide gas is a component of the atmosphere (accounting for 0.03% -0.04% of the total volume of the atmosphere), and is abundant in nature. Its production pathways mainly include the following:

① Organic matter (including animals and plants) can release carbon dioxide during the process of decomposition, fermentation, decay, and spoilage.

② During the combustion of oil, paraffin, coal, and natural gas, carbon dioxide is also released.

③ Oil and coal also release carbon dioxide during the production of chemical products.

④ All feces and humic acids can also release carbon dioxide during the fermentation and maturation process.

⑤ All animals breathe oxygen and exhale carbon dioxide.