Teaching Radioisotope Dating Using the Geology of the Hawaiian Islands

By Moran, Timothy J. | Journal of Geoscience Education, March 2009 | Go to article overview

Teaching Radioisotope Dating Using the Geology of the Hawaiian Islands


Moran, Timothy J., Journal of Geoscience Education


ABSTRACT

Students and the general public are often told that the chronology of ancient events is known with high confidence, but the methods used to determine how long ago an event occurred are usually not described or even mentioned. This gives the impression that the methods are either not important or that only scientists can understand them. Fortunately, many of the techniques are understandable if properly presented. Here one key method of dating ancient materials, argon/potassium radioisotope dating, is described in detail. In addition, a dramatic example of its calibration is described using the geology of the Hawaiian Islands. Sample lessons used in a high school physics class are described and discussed.

INTRODUCTION

Even though the accuracy of radioisotope dating has been well established (Currie, 2004; Roth and Poty, 1989), polls show that many Americans do not agree with the results. According to one recent poll, 45% of Americans believe that humans were created in their present form only a few thousand years ago, which totally contradicts the evidence from fossils dated using radioisotope dating (Gallup poll, 2004). One major reason for this discrepancy is that the isotope dating method is only rarely explained to the general public. Typically, when a textbook or news report describes a discovery about an ancient species or a human settlement, they will mention the age of the samples but give no clue about how the age was determined or the date's confidence level. This paper is intended to promote discussion of this method by arming teachers with relevant data and graphs for presenting a coherent and convincing picture of the radioisotope dating process. Hopefully the data presented here will be at least partially convincing, even to skeptics.

One likely reason that there have been limited efforts at educating non-scientists about radioisotope dating is that it requires understanding of several different science areas: chemistry, physics, geology, and math. Table 1 is a summary of the ideas that should be understood to have a full appreciation of the argon dating method.

Viewed as a group, this may seem like a challenging set of ideas. However, that is itself a reason for making radioisotope dating lessons a priority in K-12 and college courses. By presenting an example which uses knowledge from a variety of fields, students are exposed to the complexity of the scientific process, and see the importance of equipping themselves with a wide range of scientific knowledge. Applying this effort to understanding one of the most important scientific tools ever invented is a great way of demonstrating interdisciplinary science at its best.

Of the ideas listed in Table 1, the first, that atomic nuclei transform into different types of nuclei, is the foundation of the entire technique. Since students do not observe nuclear decay in their daily lives, it is understandable that they have many misconceptions about it (Prather, 2005). However, teaching students about nuclear decay is achievable, as demonstrated by Freeman et al., who emphasized developing the students' sense of place by connecting the nuclear topics with geology topics (Freeman et al., 2007).

Adding to the challenge, and the opportunity for learning, is the fact that several different types of radioisotope dating exist. Carbon dating is typically used for the study of human civilization, since it is primarily effective for samples less than 50,000 years old. Uraniumlead dating is often used for the study of the early Earth and solar system, since it is effective for samples more than a billion years old. The use of a wide range of dating tools is a point worth emphasizing to students. This paper will discuss argon dating, which is very effective for samples which are several million years old; this means that it is useful for studying genetic evolution, including human evolution.

The Hawaiian islands are a great place to study ancient geology and isotope dating because their history is easy to understand (Hawaiian Center for Vulcanology website). …

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