Tips for Teachers: Fossils

Teaching young audiences about the nature of fossils is a tricky process. For example, you’re planning a field trip that will navigate a valley with exposed Ohio shale formation and would like to spice up your lesson with the topic of fossils. Rocky River Nature Center overlooks 100 feet of the most impressive outcropping of one particular member of this formation, which I’ll refer to as Cleveland Shale. This view is widely accepted as extraordinary because a total of only 20 to 100 feet of the northeastern Ohio bedrock exists. Fort Hill, to which I’m referring, was added to the National Register of Historic Places in 1974!
 

Fort Hill, pictured from the Nature Center deck overhanging the Rocky River. This is an Ohio shale formation outcropping of Cleveland Shale. Ascending this bluff is a 135-step staircase allowing for a vantage 350 million years to the past.

Cleveland Shale is dark gray in color. You may have heard about the great armored fish Dunkleosteus and the well-preserved remains within. The massive fish and other once-living organic matter give Cleveland Shale its dark gray appearance. When explaining to your students the process behind the formation of fossils (petrification), the following tools prove to be advantageous: low-power stereoscope, flat fossil, and quartz.
 

These are the approachable tools I recommend when introducing fossils to a young audience. Rose quartz, a fern fossil in Cleveland Shale, and a low-powered stereoscopic microscope. To note, the microscope pictured here is rechargeable and thus can be used in the field.

Setup the microscope with the fossil on the stage, I prefer a fern. Do so in a way that highlights both dark and glass-like areas of the fossil. Display any silica-containing rock next to the microscope, I prefer quartz. From here, reveal that the glass-like appearance in the fossil under magnification is quartz that has replaced the space of a once-living creature. You can expect a few puzzled looks. Ask your students if they've heard of petrified wood. After pointing out the similarity in the words petrified and petrification, ask them, “Does any actual wood remain in a chunk of petrified wood?”
 

A magnified look at a fern fossil within Cleveland Shale at 10X power. Looking through the eyepiece, one can easily detect the white glass-like silica embedded in the dark gray shale.

The background on fossils will greatly enhance your students’ understanding of how fossils are formed and why they are so persistent in time. This exercise will also improve your students’ interpretation of the dark-colored Cleveland Shale along your field trip. Hopefully this routine proves valuable for your next lesson on fossils or Earth’s history.

-Marty Calabrese, Naturalist