Chapter 23 Overview

Geology is the study of the earth and the processes that shape it. Physical geology is a branch of geology concerned with the materials of the earth, processes that bring about changes in the materials and structures they make up, and the physical features of the earth formed as a result. Historical geology, on the other hand, is a branch of geology concerned with the development of the earth and the organisms on it over time. Physical and historical geology together provide a basis for understanding much about the earth and how it has developed.

One reason to study geology is to satisfy an intellectual curiosity about how the earth works. Piecing together the history of how a mountain range formed or inferring the history of an individual rock can be exciting as well as satisfying. As a result, you appreciate the beauty of our earth from a different perspective. Distinctive features such as the granite domes of Yosemite, the geysers of Yellowstone, and the rocks exposed in a roadcut take on a whole new meaning. Often, part of the new meaning is a story that tells the history and how that distinctive feature came to be.

There are many different and fascinating stories that can be read from a given landscape. The structures in the landscape, such as hills and valleys, tell a story about folding, faulting, and other building-up mechanisms, or processes, that were described in chapter 21. There is also a story about the present stage of weathering, erosion, and sculpturing, the processes that were described in chapter 22. Thus, the landscape has a story about the building and sculpturing of surface features and what this must mean about the history of the region (Figure 23.1).

The story reaching back the farthest in time is told by individual rocks. Each rock was formed by processes that were described in chapter 19. Each rock has its own combination of minerals that began to change the moment the rock was created.

Altogether, the story of the individual rock and the landscape features describes the history of the region and how it came to be what it is today. The resulting knowledge of geologic processes and events can also have a practical aspect. Certain earth materials are used for energy or for raw materials used in the manufacture of technological devices. Knowing how, where, and when such resources are formed can be very useful information to modern society.