• Guide students through a review of the rock cycle through questions and class discussion in order to create a reference point to apply new geologic information from the battle field.

• Orally quiz students on basic components of the rock cycle and provide feedback if needed.

• Provide feedback during the construction of geologic cross sections and histories, leading students to incorporate the rock cycle processes and their relationship to the battlefield.

• Review group geologic cross sections and histories, providing feedback.

“Today we’re going to connect the Union Fishhook (Lesson 1) to the rock cycle and learn to use a geologic cross section as an investigative tool.” Refer to the Battle of Gettysburg map (S-8-4_Map of the Battle of Gettysburg.doc) and facilitate a short class discussion of the map to activate prior knowledge.

“Now what can you tell me about the rock cycle?” Facilitate a short class discussion to activate prior knowledge. Go to the Exploring Earth Web site and view a rock cycle diagram at http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page03.cfm. As you view Step 3, guide your computer mouse over the arrows in the diagram to review rock-forming processes. Facilitate a class discussion. If students need a more in-depth review, Step 2 gives an animation of the processes involved and Step 3 can be expanded. “So, the rock cycle is…” Summarize class comments on the board. “Would you agree that the rock cycle models the recycling of Earth materials? How do you think the rock cycle connects with the Gettysburg battlefield?” Facilitate a brief class discussion.

“Now, let’s learn about an investigative tool that will help us interpret the Gettysburg battlefield from a rock cycle-continental rifting point of view.” If students require a visual reminder to activate prior knowledge, review the material from Lesson 2 showing an animated cross-section view of continental rifting (http://esminfo.prenhall.com/science/geoanimations/animations/35_VolcanicAct.html).

Refer to the simplified diagram of the separation of the North American and African plates approximately 190 to 230 million years ago (S-8-4-3_North American and African Plate Separation Diagram.doc). “This is a geologic cross section that represents the breakup of Pangaea. Remember, this rifting of Pangaea formed the Gettysburg basin, in the area we now call Pennsylvania, around 200 million years ago. A cross section view of the Earth, remember, shows what we would see if we cut into the Earth and moved it apart.” Facilitate a class discussion of the geologic history represented in the diagram. In general: 1) Heat energy from inside the Earth creating buoyant material, which created convection currents. These rising and falling currents pulled the North American (Pennsylvania) and African plates apart. 2) As the plates diverged: a) the lithosphere broke and shifted down along faults (relative movement indicated by the paired arrows along the sides of the basin), forming the Gettysburg rift basin; and b) magma formed beneath the basin and began to rise to the Earth’s surface. 3) The magma intruded between pre-existing sedimentary rock layers in the basin, producing sills like the Gettysburg sill.

“So, how does this geologic cross section help us understand the Gettysburg battlefield in terms of rock recycling? Let’s focus on the sedimentary rocks and the igneous rocks in the area. Where did they come from?” Other rocks. As the Gettysburg basin formed, rocks from the surrounding area weathered into smaller pieces (sediments), which were dumped (deposited) in a low area (the Gettysburg basin). These sediments became the sedimentary rocks in the Gettysburg battlefield. Mantle rock material melted to become the magma that intruded the sedimentary rocks in the Gettysburg battlefield, forming the Gettysburg sill. The sedimentary rocks and the igneous sill are weathering into sediment. These sediments are eroding and being deposited to form new sedimentary rocks.

“The hills and ridges in the Gettysburg battlefield are underlain by igneous rocks. The valleys are underlain by sedimentary rocks. Why is the igneous rock associated with higher terrain and sedimentary rocks with the lower terrain?” The sedimentary and igneous rocks weather at different rates. The sedimentary rocks weather more rapidly and are eroded away, leaving the igneous rock behind as hills and ridges. This is called differential weathering. Differential weathering sculpts the terrain of an area.

“Now you are going to work in groups. You will sketch out the geologic cross section we just discussed and write a narration of the geologic history of the Gettysburg battlefield area. Each group will report to the rest of the class.”

Group students. Distribute the butcher paper and markers. Leave the cross section projected so students will have a model from which to work.

Extension:

• Students will construct a diagram of the rock cycle, including significant geological events in place of significant features. Brief information and an estimated date or time frame of the events will be included on the diagram along with the basic components of the rock cycle (rock types, processes, locations).

Example:

Students will include the rifting process responsible for some of the geological features at Gettysburg (i.e., rifting, sedimentation, igneous rock formation).

• Students hypothesize what will happen to the rock cycle if the heat from the Earth’s interior has significantly increase. Students will highlight the following in their responses:

• Production of magma/lava

• Structure of the Earth’s interior

• Ratio of interior layers (core, mantle, crust)

• Effect on living organisms on the crust

  Students will present their responses in essay form.

Answer: There will be no more rock cycle. Tectonic plates will not move; all geologic activity will cease; Earth will become a dead planet geologically; Earth materials will recycle no more.