Geologic Timeline Helper

I like to assign groups of about 4-5 students and have a relaxing art day from time to time. Having your students build a proportional geologic timeline on a large poster or paper roll is a great way to impress upon students how old the Earth is, and how briefly multi-cellular life forms, and humans in particular, have been around. Each group could build the entire thing or you could have each group do a particular period of time and assemble it at the end. Interesting things to note for each period are positions of the continents, atmospheric oxygen level, atmospheric carbon dioxide level, average surface temperature, sea level relative to today. All of this information is available in the Wikipedia links. Students figure out how long their timeline will be (the total age of the Earth) and then divide the timeline up into the major geologic periods. Drawings of representative organisms common to the period, and major Earth events (ice ages, comet bombardments, major extinction events) should be visually depicted.

Instructions: Enter a value (in inches or centimeters) for the total length of your geologic timeline, and the table will output the length (in your units) that each geologic period needs to be for proper scaling. For example, try values of 100 centimeters or 72 inches. Here's a great graphic with representative life forms. Click here or here to purchase the poster.

Grading: I use peer assessment when evaluating group work. I use a rubric to grade the group project, and a peer evaluation ballot for each group member to fill out privately, grading both themself and their peers. Although people new to peer assessment are sometimes skeptical, I have found that students, when given a rubric and graded work samples (from previous years' students), generally grade the projects of their peers objectively, and grade the work of their fellow group members accurately most of the time. I throw out the grades they give their own work, and the grade they give themselves as a group member if they are inflated, but I ask them them to self-evaluate in order to look for conflicts and get information about the group dynamic that I may not have observed.