Part B: Determining Relative Age

The youngest unit is composed of the prominent dark wedges that run diagonally from NW to SE. The next youngest unit contains gray bands that run from W to E, and fork several times. The oldest unit contains the bright icy plains.

Part C: Reconstructing the Landscape

Click here for an outlined version (one possible solution) to the Wedges puzzle.

As the prominent dark wedge at left is removed, the remaining pieces will have to slide together AND rotate to be aligned. It is very important that students recognize both types of motion. Note that some features that match up as a result of this step are even younger still (small fractures that the students were instructed to avoid), whereas others truly represent old features that were separated by the creation of the wedges.

1) Sliding past (faulting), moving together, rotation

2) The fact that some of the plates had to be rotated suggests that there is a liquid or ductile material supporting them from below.

3) Graph should show a linear relationship. The youngest wedges may have higher ridges that produce greater shadows; Over time, the surface might be coated by a light-colored material such as frost; Darker material in the wedges may sink through the ice with time; Other plausible explanations.

4) It would probably be dark.

5) They probably formed as the result of material filling in the cracks from below. The fact that there is no missing material from the edges of adjacent plates supports this interpretation.

6) a. Crustal plates in other regions would have to be destroyed.

b. The crust might subduct and melt, or evaporate/sublimate into space.

7) At its widest point, the dark wedge is approximately 11 miles wide. Dividing this distance by 100 million years gives a rate of 1.1 x 10 ^-7 miles/year, or .006 inches/year. Answers will vary slightly.

Grades K-4

• Use the Galileo E11 image, "Regional Mosaic of Chaos and Gray Band," instead of the Wedges image.

Grades 9-12

• Have students create a short video or flip-chart showing the motion of the crust in this region over time.
• Have students use image processing software (such as NIH Image) to determine the differences in shading for the three different geologic units. Assign arbitrary ages to the end members, and then determine a rate of shading change. Using this value, determine the relative age for the middle unit. Is it closer in age to the dark wedges or the background plains?

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Galileo Solid State Imaging Team Leader: Dr. Michael J. S. Belton

The SSI Education and Public Outreach webpages were originally created and managed by Matthew Fishburn and Elizabeth Alvarez with significant assistance from Kelly Bender, Ross Beyer, Detrick Branston, Stephanie Lyons, Eileen Ryan, and Nalin Samarasinha.

Last updated: September 17, 1999, by Matthew Fishburn

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