Life Science Curriculum 8-12
Submitted by: Martin King
Institution: Azusa Pacific University
Title of Experiment: The Layered and Dynamic Earth
2 cardboard boxes, ideally shoeboxes (One
for scraps and the other for demonstration)
Pair of sharp scissors
4-5 sheets of plain, white paper
Clear scotch tape
Permanent markers (any colors will do)
1 or 2 cardboard blocks
Scientific Background of Experiment:
Plate tectonics is a relatively new theory that has revolutionized the way geologists think about the Earth. According to the theory, the surface of the Earth is broken into large plates. The size and position of these plates change over time. The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building. Plate tectonics is a combination of two earlier ideas, continental drift and sea-floor spreading. Continental drift is the movement of continents over the Earth's surface and in their change in position relative to each other. Sea-floor spreading is the creation of new oceanic crust at mid-ocean ridges and movement of the crust away from the mid-ocean ridges.
The Earth is divided into three chemical layers: the core, the mantle and the crust. The core is composed of mostly iron and nickel and remains very hot, even after 4.5 billion years of cooling. The core is divided into two layers: a solid inner core and a liquid outer core. The middle layer of the Earth, the mantle, is made of minerals rich in the elements iron, magnesium, silicon, and oxygen. The crust is rich in the elements oxygen and silicon with lesser amounts of aluminum, iron, magnesium, calcium, potassium, and sodium. There are two types of crust: oceanic crust which is made primarily of relatively dense rock called basalt and continental crust which is made up of less dense rocks such as andesite and granite.
The ways that plates interact depend on their relative motion and whether oceanic or continental crust is at the edge of the lithospheric plate. Plates move away from, toward, or slide past each other. Geologists call these divergent, convergent, and transform plate boundaries. At a divergent plate boundary lithospheric plates move away from each other. At a convergent plate boundary, lithospheric plates move toward each other. At a transform plate boundary, plates slide past each other.
This experiment demonstrates the dynamic motions of plate tectonics in virtual and physical aspects.
1. Cut a narrow slit in the top of a box.
2. Cut a larger square in the side of the box.
3. Slide two pieces of paper through the slit and about half-way into the box.
4. Tape a block of cardboard or folded paper on the outside edge of one sheet of paper. The plain sheet of paper represents an oceanic plate. The sheet with the cardboard represents a plate with oceanic and continental crust. Note that the continental crust rises above the oceanic crust.
5. Demonstrate motion at a divergent plate boundary by pushing the paper up from inside the box. The sheets of paper will move away from each other just like new oceanic crust at mid-ocean ridges.
6. Demonstrate motion at convergent plate boundaries by pulling the plain sheet of paper down from inside the box. Move the sheet with the continent so that the continent is adjacent to the narrow slit. The oceanic plate will disappear beneath the edge of the continent just like oceanic crust at subduction zones.
7. Magnetic anomaly patterns can also be demonstrated with the box. Use two plain sheets of paper. With a thick (1 inch) marker, draw on the sheets above the slit. The strip of marked paper represents rocks that are magnetized during a magnetic normal period.
8. Push the paper up from inside the box and expose unmarked paper. The unmarked paper represents rocks that are magnetized during a magnetic reversed period.
9. Create more oceanic crust by pushing the sheets out of the slit and drawing along the slit with the marker.
10. Repeat until the sheets are covered with black (magnetic normal) and white (magnetic reversed) parallel lines. Note that the patterns on each sheet (plate) are symmetrical with respect to the slit (mid-ocean ridge).
11. The convergence and collision of two plates with continental crust can also be demonstrated. Tape cardboard blocks on the outside of each sheet of paper.
12. Pull the two sheets into the box through the slit. Note that the sheets are disappearing into the slit similar to oceanic plates at a subduction zone. As the sheets (plates) are consumed, the continents move closer together and ultimately collide. Such a collision is currently forming up the Himalaya Mountains.
Misc. Helpful Information/ Hints/ Suggestions:
- It is very important that the aspects of magnetic anomalies and plate boundaries be understood in order to carry out this experiment.
- Tutorials or study guides might be of some use.
- The website: http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics.html will be of very good use!