6. Relative and Absolute Dating

    Adapted by Sean W. Lacey & Joyce M. McBeth (2018) University of Saskatchewan from Deline B, Harris R, & Tefend K. (2015) “Laboratory Manual for Introductory Geology”. First Edition. Chapter 1 “Relative and Absolute Dating” by Bradley Deline, CC BY-SA 4.0. View Source.

6.1 INTRODUCTION

To develop a history of how geologic events have acted on the Earth through time, we need to understand what and when geological processes have occurred through Earth’s history. Geologists learn about what processes occur on Earth through studying the rock record and observing geologic processes in modern environments. To understand when these processes have acted during Earth’s geologic time, geologists make observations about the relationships of rocks to one another in the rock record, using a process called relative dating. Geologists use this information to construct models for how these relationships developed. For example, if the rock record in an area contains sedimentary rocks that are folded, a model to explain those relationships would start with a region where sediments were deposited, followed by lithification of the sediments to form rock, then the rocks would be subjected to tectonic pressures that folded the rocks. Using relative dating techniques, we know those events occurred in that order, but not when they occurred precisely in time. To add specific dates for the events in the model, geologists can use absolute dating techniques to date the rocks (determine their age). Geologists develop models such as this at locations all across Canada, North America, and around the globe. Each location geologists study may only provide information on Earth history from a short window in time; collectively, however, the information in these models can be used to develop our understanding of processes that have acted on Earth since it first formed.

In this chapter, you will learn about how to determine the relative ages of rocks and calculate the absolute ages of rocks.

6.1.2 Learning Outcomes

After completing this chapter, you should be able to:
• Discuss the importance of time in the study of geology
• Discuss the difference between relative dates and absolute dates
• Apply geologic laws and stratigraphic principles in the relative dating of geologic events
• Use radiometric dating data and calculations to determine the absolute date of rock units

6.1.3 Key Terms

• Absolute dating
• Angular unconformity
• Radiometric (Carbon-14) dating
• Daughter atom
• Disconformity
• Geologic laws and stratigraphic principles
• Geologic time scale
• Half-life
• Isotope
• Law of superposition
• Nonconformity
• Principle of cross-cutting relationships
• Principle of faunal succession
• Principle of original horizontality
• Principle of lateral continuity
• Parent atom
• Potassium-Argon (K-Ar) dating
• Radiometric dating
• Relative dating
• Unconformity
• Uranium-Lead (U-Pb) dating