Chapter 8: Geologic Time

Chapter 8: Geologic Time

Fig. 8.13

OBJECTIVES

? Define, compare, and contrast relative and absolute age dating.

? Describe the development of ideas that led to the modern view of geologic time.

? List and explain the rules that geologists apply to determine the relative age of geologic events.

? Explain how correlation allows individual rock layers to be traced from one place to another.

? Describe how relative dating methods allowed the geologic time scale to be established.

OBJECTIVES

? Summarize radioactivity and its use in determining the absolute age of geologic events.

? Explain how absolute dating has established numerical ages for the geologic time scale.

? Explain how relative and absolute dating together form the basis of our modern understanding of Earth history.

? Discuss how the vast span of geologic time has allowed plate tectonics to profoundly influence Earth history.

Geologic Time: An Overview

? Most of the processes that shape Earth operate extremely slowly ? in vast geologic time.

? Geologists use two main methods of measuring geologic time. ? Relative age ? Absolute age

? These methods have been used to establish a geologic time scale.

Fig. 8.9b

Measuring Geologic Time: Relative and Absolute Ages

? Relative Age ? Age based on order in which geologic events occurred

? Absolute Age ? The amount of time elapsed since the rock formed ? May be based on measurement of radioactive decay

? Final determination of the sequence of a particular set of geologic events is usually found by combining clues from the outcrop that reveal relative age, along with evidence from laboratory measurements of absolute age.

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