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Shades of History 

This is more of a demonstration than an activity usingregular classroom window shades. The cross-sectionsshown have actually been carefully thought out to be

useful for several levels of geologic history instruction.

To make the shades, it is important to first of all getpermission from any administrator who will get tickedoff at permanently defacing the shades!

Second, plan it out well. Think about what you want theshades to show. I started with index cards and sketches.

 When drawing on the shades, be sure to account for thefact that the shades roll up and cover the drawing. It

 would be a shame to make a beautiful drawing on tohave it too long to completely display. I also includedsurface features (trees and people) to show that theseare exposures.

 

 At the first level each shade makes a good sequence of events to solve. At this point, do notdiscuss the significance of the fossils or the heavy red line.

Shade #1 shows a sequence highlighting superposition with unconformities. (click the shades for a largerpicture)

 

Shade #2 focuses on a fault and then an unconformity above it. This one is particularly useful because yourarely see sequences that have deposition after a fault.Students need to see how younger layers will continue

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to be deposited flat and level after a disturbance(folding, tilting and faulting). This is evident in thelimestone layer that is thick on the left and thin on theright but flat on the top.

Shade #3 shows an igneous intrusion.

 

Shade #4 shows another intrusion but this time wedon’t see the magma pipe coming from the bottom(also something that is rarely shown in these types of puzzles).

 

 At the next level, the shades can be used to illustratecorrelation. Each section matches well with the others

 but each section has some unique difference to make ita little less obvious and more challenging. Note thatshades 3 & 4 exactly fit together but are made atdifferent heights to illustrate uplift of one area. Only 

 when the shades are offset do the layers re-align. It isparticularly interesting to point out that in shade #1there is a very big gap represented by the unconformity 

 because this sequence shows both the oldest (trilobite)and youngest (human) fossils separated by only a few layers.

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For the last level, the shades lead to a discussion of volcanic time markers and asteroid impacts. At first I say the line is like a volcanic marker and every layer just below it was formed at thesame time. Finally, the true identity of the red line is revealed when you get to discuss asteroid

impacts and the significance to the end of the dinosaurs.

 

The shades seem to be most effective when you don’t really give them too much attention anduse them as aides for very small bites of information.

Fifteen years of Medina On-Line

1994-2009Email: mrsciguy@optonline.net