Physical geology is the study of the earth's rocks, minerals, and soils and how they have formed through time. Complex internal processes such as plate tectonics and mountain‐building have formed these rocks and brought them to the earth's surface. Earthquakes are the result of the sudden movement of crustal plates, releasing internal energy that becomes destructive at the surface. Internal heat and energy are released also through volcanic eruptions. External processes such as glaciation, running water, weathering, and erosion have formed the landscapes we see today.
About 2300 years ago, the Greeks, led by the philosopher Aristotle, were among the first to try to understand the earth. During the 1600s and 1700s, scientists believed the earth had been produced by gigantic, sudden, catastrophic events that built mountains, canyons, and oceans.
In the late 1700s, James Hutton, a Scottish doctor, proposed that the physical processes that shape the world today also operated in the geologic past—a principle known as uniformitarianism. Another early concept was the law of superposition—in an undeformed sequence of sedimentary rocks, each layer is younger than the ones below it and older than those above it. The law of faunal succession states that fossils in these rocks occur in the same kind of order, and changes in fossil content represent changes in time. Thus, rocks from different parts of the world containing the same type of fossil formed about the same time. English geologist Charles Lyell enlarged on these ideas and modernized geology with his series of books in the mid to late 1800s.