Although the science of geology as we know it today is a relatively young field, insightful observations of Earth processes were made as far back as the ancient Greeks. Some of these early ideas were handed down through the ages. For example, Herodotus (c. 484-425? B.C.E.) had rather modern insights about the formation of the Nile River delta and the important role sediment (deposited by flooding) played in producing the fertile Nile Valley. The Greek historian also applied a primitive form of a principle known as uniformitarianism, the idea that existing processes are sufficient to explain all geological changes that have occurred over time.

But many other “geological” observations by the ancient Greeks seem fanciful today. Por example, Aristotle (384-322 B.C.E.), the famous philosopher and tutor to Alexander the Great, believed that the heat from volcanic eruptions was produced by underground fires. He also believed that air moving through caverns became heated by friction, causing these fires.