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Mapping Ancient Coastlines

Summary:
Students draw the location of ancient coastlines onto a bathymetric contour map. Materials:

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Source:
Adapted by Windows to the Universe team member Lisa Gardiner from a University of Georgia introductory geology activity.
Grade level:
7 - 12
Time:
15-20 minutes class time
Student Learning Outcomes:
  • Students interpret a graph to understand how sea level has changed.
  • Students map ancient coastlines using their understanding of contour lines and their interpretation of the sea level graph.
Lesson format:
Worksheet

National Standards Addressed:

DIRECTIONS:

  1. Describe to students what contour lines are. Our "Mapping Potato Island" activity is an excellent way to introduce this concept. While a topographic map has contour lines that describe the shape of the land surface, a bathymetric map has contour lines that describe the shape of the ocean floor. Bathymetric maps, like topographic ones, use sea level as a reference point.
  2. Familiarize students with the graph at the top of their worksheets. This graph describes sea level change over time. Global sea level changes in recent geologic history have been due to repeated formation and melting of glaciers which move water onto land, away from oceans.
  3. Students use the graph to find the sea level at various times in the past (Answers: -124 meters; -75 meters; approx -40 meters; approx -135 meters) then draw ancient coastlines onto their bathymetric map following contour lines.
  4. The final question involves the likely age of archeological sites that were once along a coast. If it must be less than 20,000 years ago (because there were no people living in that area before that time), then the answer must be about 10,000 years ago.

BACKGROUND INFORMATION:

Contour lines are imaginary lines that connect places of equal elevation. If you were taking a hike along a hillside and not walking either uphill or downhill, you would be walking on a contour line. When contour lines are close together, the slope is very steep. When contour lines are far apart, the slope is very shallow. Maps that show the shape of the ocean floor with contour lines are called bathymetric maps.

Sea level change has happened at various times in Earth history. Global sea level can rise because glaciers melt, adding water to the oceans, or when plate tectonic movements shallow the ocean basins displacing water onto the edges of continents. It is a natural process that has gone on since there have been oceans on Earth! Over recent geologic history, sea levels have changed rapidly by geologic standards due to the repeated formation and melting of glaciers.

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