Description
Each statement represents the primary learning objective for the corresponding major heading within the chapter. After you complete the chapter you should be able to:
1.1 Distinguish between physical and historical geology and describe the connections between people and geology.
1.2 Summarize early and modern views on how change occurs on Earth and relate them to the prevailing ideas about the age of Earth.
1.3 Discuss the nature of scientific inquiry, including the construction of hypotheses and the development of theories.
1.4 List and describe Earth’s four major spheres.
1.5 Define system and explain why Earth is considered to be a system.
1.6 Outline the stages in the formation of our solar system.
1.7 Describe Earth’s internal structure.
1.8 Sketch, label, and explain the rock cycle.
1.9 List and describe the major features of the continents and ocean basins.
The spectacular eruption of a volcano, the terror brought by an earthquake, the magnificent scenery of a mountain range, and the destruction created by a landslide or flood are all subjects for the geologist. The study of geology deals with many fascinating and practical questions about our physical environment. What forces produce mountains? Will there soon be a major earthquake in California? What was the Ice Age like, and will there be another? How were ore deposits formed? Where should we look for water? Will plentiful oil be found if a well is drilled in a particular location? Geologists seek to answer these and many other questions about Earth, its history, and its resources.
Geology: The Science of Earth
The subject of this text is geology, from the Greek geo (Earth) and logos (discourse). Geology is the science that pursues an understanding of planet Earth. Understanding Earth is challenging because our planet is a dynamic body with many interacting parts and a complex history. Through-out its long existence, Earth has been changing. In fact, it is changing as you read this page and will continue to do so into the foreseeable future. Sometimes the changes are rapid and violent, as when landslides or volcanic eruptions occur. Just as often, change takes place so slowly that it goes unnoticed during a lifetime. Scales of size and space also vary greatly among the phenomena that geologists study. Sometimes geologists must focus on phenomena that are submicroscopic, and at other times they must deal with features that are continental or global in scale.
Physical and Historical Geology
Geology is traditionally divided into two broad areas—physical and historical. Physical geology, which is the primary focus of this book, examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface
(FIGURE 1.1). The aim of historical geology, on the other hand, is to understand the origin of Earth and its development through time. Thus, it strives to establish an orderly chronological arrangement of the multitude of physical and biological changes that have occurred in the geologic past. The study of physical geology logically precedes the study of Earth history because we must first understand how Earth works before we attempt to unravel its past. It should also be pointed out that physical and historical geology are divided into many areas of specialization. Every chapter of this book represents one or more areas of specialization in geology.
Geology is perceived as a science that is done outdoors and rightly so. A great deal of geology is based on observations, measurements, and experiments conducted in the field. But geology is also done in the laboratory where, for example, the analysis of minerals and rocks provides insights into many basic processes and the microscopic study of fossils unlocks clues to past environments (FIGURE 1.2). Frequently, geology requires an understanding and application of knowledge and principles from physics, chemistry, and biology. Geology is a science that seeks to expand our knowledge of the natural world and our place in it.
Geology, People, and the Environment
The primary focus of this book is to develop an under-standing of basic geologic principles, but along the way we will explore numerous important relationships between people and the natural environment. Many of the problems and issues addressed by geology are of practical value to people.
Natural hazards are a part of living on Earth. Every day they adversely affect millions of people worldwide and are responsible for staggering damages (FIGURE 1.3). Among the hazardous Earth processes that geologists study are volcanoes, floods, tsunamis, earthquakes, and landslides. Of course, geologic hazards are natural processes. They become hazards only when people try to live where these processes occur.
According to the United Nations, in 2008, for the first time, more people lived in cities than in rural areas. This global trend toward urbanization concentrates millions of people into megacities, many of which are vulnerable to natural hazards. Coastal sites are becoming more vulnerable because development often destroys natural defenses such as wetlands and sand dunes. In addition, there is a growing threat associated with human influences on the Earth system; one example is sea-level rise that is linked to global climate change. Some mega-cities are exposed to seismic (earthquake) and volcanic hazards where inappropriate land use and poor construction practices, coupled with rapid population growth, are increasing vulnerability.
Resources represent another important focus of geology that is of great practical value to people. They include water and soil, a great variety of metallic and nonmetallic minerals, and energy (FIGURE 1.4). Together they form the very foundation of modern civilization. Geology deals not only with the formation and occurrence of these vital resources but also with maintaining supplies and with the environmental impact of their extraction and use.
Geologic processes clearly have an impact on people. In addition, we humans can dramatically influence geologic processes. For example, river flooding is natural, but the magnitude and frequency of flooding can be changed significantly by human activities such as clearing forests, building cities, and constructing dams. Unfortunately, natural systems do not always adjust to artificial changes in ways that we can anticipate. Thus, an alteration to the environment that was intended to benefit society often has the opposite effect.
At appropriate places throughout this book, you will have an opportunity to examine different aspects of our relationship with the physical environment. It will be rare to find a chapter that does not address some aspect of natural hazards, environmental issues, or resources. Significant parts of some chapters provide the basic geo-logic knowledge and principles needed to understand environmental problems.