Eighth Edition
by Harold L. Levin

Chapter 1 - page 1

The Science of Historical Geology

Pamela J. W. Gore
Georgia Perimeter College

Introduction

The Earth formed about 4.6 billion years ago.

Homo sapiens appeared on Earth between about 300,000 and 150,000 years ago.

Humans ask questions about their surroundings.
How did the Earth form? Why do earthquakes occur? What lies beneath the land and below the ocean floor?

Curiosity leads to exploration.

Why Study Earth History?

The Earth has changed through time. Understanding past events will help us predict future events.

Examples of past geologic events and changes to the Earth:

• Continents have been flooded by inland seas.
• Continents have drifted across the globe and collided with one another to form mountain ranges.
• Glaciers have covered large parts of the continents.
• Earthquakes.
• Volcanic eruptions.
• Meteorite and asteroid impacts.
• Changes in the chemistry of the oceans and atmosphere.
• Life on Earth has changed through time. Sometimes slowly, sometimes swift and deadly.

All of these past events are relevant to our lives today.

Geology

Geology is the study of the Earth. Geology deals with Earth materials, processes, and the history of the Earth and life.

Two major branches of geology:

• Physical Geology - deals with Earth materials and processes
• Historical Geology - deals with origin and changes of Earth and life through time and space.

Historical geologists look at the results of past events and work backward in time to discover the causes of those events.

Exploration geologists search for fossil fuels and mineral resources. They must have knowledge of Earth history to understand where to find energy and mineral resources. They must also understand astronomy, physics, chemistry, biology, and mathematics.

Because geology incorporates information from many other sciences, it is referred to as a "multidisciplinary" or "eclectic" science.

Scientific Method in Geology

Science operates through the use of the Scientific Method.

The scientific method is a method for finding answers to questions and solutions to problems.
Scientists work like detectives to gather data, to try to figure out what happened.
The data may be obtained through observations and/or experiments, which can be repeated and verified by others.

Typically, a number of ideas or interpretations are developed to explain what happened. Each idea or interpretation is called a hypothesis.
When scientists come up with several possible explanations, that is called the "method of multiple working hypotheses." Each hypothesis is tested, and may be accepted, or rejected, or modified.

Generally, when evaluating several hypotheses which appear to be equally valid, the simplest explanation is the one selected to explain the observations.

A hypothesis that survives repeated challenges, and is supported by a large body of evidence, may be elevated to the status of a theory. A theory is not just a wild idea or a guess. Theories have survived close examination, and can be accepted with confidence. A theory has a very high probability of being correct. Examples of theories include the theory of relativity, plate tectonics theory, evolutionary theory, and atomic theory.

If a theory triumphs over every challenge, it can be raised to the level of a scientific law, such as the "Law of Gravity." Laws are often explained mathematically.

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Document created by: Pamela J. W. Gore
Georgia Perimeter College, Clarkston, GA

September 2, 2005