Chapter 1 Introduction to studying the Earth

Chapter 1 Introduction to studying the Earth - 2009 Allan...

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CHAPTER 1 © 2009 Allan Ludman and Stephen Marshak W.W. Norton & Company Setting the Stage for Learning about the Earth PURPOSE To help you begin your study of the Earth, Chapter 1 will • introduce the challenges geologists face when studying a body as large and complex as the Earth; • show how to use concepts of dimensions, scales, and orders of magnitude, to describe the Earth; • briefly review the materials and forces you will encounter when studying the Earth; • introduce the ways in which geologists discuss ages, geologic materials and events, and the rates at which geologic processes take place. • help you become familiar with the basic types of diagrams and images used by geologists. MATERIALS NEEDED • a triple-beam or electronic balance • a 500 ml graduated cylinder • a metric ruler • a calculator • a compass 1.1 THE CHALLENGE OF STUDYING A PLANET Learning about the Earth is like training to become a detective. Both geologists and detectives need keen powers of observation, curiosity about slight differences, broad scientific understanding, and instruments to analyze samples. And both ask the same questions: What happened? How? When? Although much of the thinking is the same, there are big differences. A detective’s “cold case” may be 30 years old, but “old” to a geologist means hundreds of millions or billions of years. To a detective, a “body” is a human body but to a geologist a body may be a mountain range or a continent. Eyewitnesses can help detectives, but not geologists because for most of Earth’s history there weren’t any humans. To study the Earth, geologists must therefore think differently from other kinds of investigators. The overall goal of this manual is to help you look at the Earth and think about its mysteries like a geologist. To illustrate geologic thinking, let’s start with a typical geologic mystery. Almost 300 years ago, settlers along the coast of Maine built piers to load and unload ships. Some of these piers are now submerged to a depth of 1 m (39 inches) below sea level (Figure 1.1). Tourists might not think twice about this before heading for a lobster at the local restaurant, but a geologist would want to know how rapidly the pier was submerged and what caused the submergence. How would a geologist go about tackling this problem? 1
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Figure 1.1: Subsidence along the coast of Maine Let’s first calculate the submergence rate. Since we haven’t been watching the pier constantly for 300 years, we have to make some assumptions – geologists often do this to make estimates. Assume that the piers were originally 1 m above sea level as many are today, and that submergence occurred at a constant rate. With these assumptions calculating the rate of submergence for the past 300 years becomes simple arithmetic. Exercise 1.1a: Submergence rate along the Maine coast.
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Chapter 1 Introduction to studying the Earth - 2009 Allan...

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