To help students understand the development of the geologic time scale.
Also, to introduce students to the major time periods in earth's history, as well as to the role fossils play in helping us understand this history.
Another thing to decide on before class is how many bags you will be able to make.
Ideally, you would have 4 bags per lab group, but depending on the limiting number of supplies you have, you can just make a minimum of 4 bags and rotate them between groups.
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.
Students will likely have been introduced to the geologic time scale in earlier grades, so this lesson is structured loosely to enable you to adapt the content to match the levels and needs of your particular students.
Depending on the number of different colored beads you have available, you can do just one or several different isotopes.
Each isotope you choose needs two different colors of beads associated with it and the total of number of beads per bag will be 100 (this creates the simplest math, but you could use less beads and have them calculate percentages if necessary).
Basic understanding of how radiometric dating works is useful.
This lesson is highly simplified, and the powerpoint describes everything the student will need to know for the activity.