observational study

Research that gathers data in a real-world setting without intentionally manipulating any variable. (Chapter 2)

observations

Information detected with the senses—or with equipment that extends our senses. (Chapter 2)

oil

A liquid fossil fuel useful as a fuel or as a raw material for industrial products. (Chapter 19)

open dumps

Places where trash, both hazardous and nonhazardous, is simply piled up. (Chapter 7)

organic agriculture

Farming that does not use synthetic fertilizers, pesticides, or other chemical additives like hormones (for animal rearing). (Chapter 17)

overburden

The rock and soil removed to uncover a mineral deposit during surface mining. (Chapter 18)

overpopulation

More people living in an area than its natural and human resources can support. (Chapter 4)

ozone

A molecule with three oxygen atoms that absorbs UV radiation in the stratosphere. (Chapter 2)