Teaching radiometric dating
In the Grand Canyon, the layers of strata are nearly horizontal.
Most sediment is either laid down horizontally in bodies of water like the oceans, or on land on the margins of streams and rivers.
For example, in the rocks exposed in the walls of the Grand Canyon (Figure 1) there are many horizontal layers, which are called strata.
The study of strata is called stratigraphy, and using a few basic principles, it is possible to work out the relative ages of rocks.
This 5-12-grade activity introduces students to the idea of sequencing information in overlapping data sets and the Principle of Superposition, which is a core concept in relative dating. Offers history of age dating, stratigraphic principles, rock correlation, fossil correlations, radiometric dating, and the geologic time scale. Short discussion of radioactive dating and stratigraphic principles.
Radiometric Dating and the Geologic Time Scale, The Talk Origins Archive. Provides brief overview of (1) relative dating and stratigraphic methods, (2) absolute dating and radiometric dating, including a table with parent to daughter isotopes and half lives of those isotopes commonly used in radiometric dating, (3) paleomagnetics and (4) geologic time. Includes tables of common radioactive parent isotopes and their stable daughter products, and half lives of common radioactive isotopes.
Geologists have established a set of principles that can be applied to sedimentary and volcanic rocks that are exposed at the Earth's surface to determine the relative ages of geological events preserved in the rock record.
Thus, any deformations of strata (Figures 2 and 3) must have occurred after the rock was deposited.
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
The idea of radioactive decay and half lives, a type of absolute dating, is shown through an activity using M&M's candy and graph paper. Sequencing Time, University of California, Berkeley. This 5-12-grade activity lets students place parts of their own life story into a time line so that they can better understand how geologic time is reconstructed by scientists.
Who's on First, University of California, Berkeley. This website is a book chapter about geologic time. This online version of their informative booklet contains short, content explanations about relative time, major geologic time divisions, index fossils for use in age dating, radiometric dating and the age of the earth.
The site also provides fact sheets on the age of the Earth and isochron dating.