Which of the following is an example of a natural source of air pollution

Robert Hazen’s studied enviromental and biological processes that might have been critical for life, and also for the formation of approximately two-thirds of Earth's mineral species (see Hazen et al., 2008; Gonzalez & Richards 2020) .

Explanation:

Hazen provided evidence about how first organic molecules were generated on the primitive earth millions of years ago. He observed that high-pressure hydrothermal vents may provide food for underwater ecosystems. It represents a piece of critical evidence on the origin of life.

You can read these articles that are certainly clarifying in the description of his experiments and discoveries:

1- Hazen, R. M., Papineau, D., Bleeker, W., Downs, R. T., Ferry, J. M., McCoy, T. J., ... & Yang, H. (2008). Mineral evolution. American Mineralogist, 93(11-12), 1693-1720.

2- Gonzalez, G., & Richards, J. W. (2020). The privileged planet: how our place in the cosmos is designed for discovery. Gateway Editions.