Final answer:
Natural sources of variable gases and materials include volcanic eruptions, ocean currents, and biological processes. The combustion of fossil fuels is not considered a natural source.
Step-by-step explanation:
Natural sources of variable gases and materials include volcanic eruptions, ocean currents, and biological processes. The combustion of fossil fuels is not considered a natural source. Volcanic eruptions release gases such as carbon dioxide and sulfur dioxide into the atmosphere. Ocean currents can transport gases such as oxygen and carbon dioxide. Biological processes, such as respiration and decomposition, also release gases into the environment.