Glossary of "Environmental Science: Earth as a Living Planet (2nd ed.)" by Botkin & Keller (1998)
- The principle that processes that operate today operated in the past. Therefore observations of processes today can explain events that occurred in the past and leave evidence, for example, in the fossil record or in geologic formations.
- Botkin, D. B. & Keller, E. A. 1998. Environmental Science: Earth as a Living Planet, 2nd ed. -xxxxii + 649 pp. John Wiley & Sons, Inc., New York.