The Norwood Science Center Geology (Minerals) Grade 4 Background Information: Where do rocks come from? At first you might think the answer to this question is simple. Igneous rock comes from either magma or lava that has cooled. Sedimentary rock comes from either sediments or other materials that have been cemented and packed together. Metamorphic rock comes from other rocks that have been changed. Yet when you think again, you can see that the answer is not very simple. Magma and lava are melted rocks. Sediment is made of broken rocks. Metamorphism only occurs with existing rock. Thus, rocks come from other rocks. Rocks that exist today will change in time into different rocks. All rocks are part of an ongoing cycle. The Rock Cycle is a neverending process by which rocks change from one type to another. For example, lava cools and hardens into igneous rock. Igneous rock breaks into sediments, which form sedimentary rock. Under heat and pressure (or both) sedimentary rock changes into metamorphic rock. Metamorphic rock may change into magma. The magma may harden into new igneous rock. There are shortcuts in the cycle as well. Igneous rock may not always break into sediments. If igneous rock is buried, heat and pressure may change it directly into Rock Cycle Gr. 4 Page 1
metamorphic rock. Metamorphic rock may break into sediments that form sedimentary rock. You may wonder how the rock cycle got started. Evidence suggests that the Earth was once made entirely of magma. It is believed that the first rocks formed as the magma cooled. Thus the rock cycle probably began with igneous rock. TITLE: PURPOSE: MATERIALS: THE ROCK CYCLE Create a three dimensional model of the rock cycle (per group of three students) Two sticks of clay of different colors Wax paper Rock Cycle Worksheets (for the classroom teacher) Plastic knife PROCEDURE: Advanced preparation: 01. Using the plastic knife cut each stick of clay into eight pieces. A simple technique might be to divide the stick in half, then each half into quarters, and the quarters into eighths. Note: clay may be delivered pre-cut. Rock Cycle Gr. 4 Page 2
Classroom lesson: 02. Distribute a piece of wax paper to each group along with two colors of clay blocks and one worksheet. 03. Read aloud Part #1 from "The Rock Story" (see attached). 04. Each single color piece of clay will be a model of a small piece of granite, an igneous rock. Instruct students to divide each block into two equal pieces. Have them place half of each color clay on the section of the worksheet marked igneous where it will remain throughout the lesson. The remaining two pieces are placed on the wax paper. 05. Students should divide each piece of clay on the wax paper into three equal parts. Each team member should take a piece of each color. 06. Read Part #2 from The Rock Story. 07. The students should then divide each piece into four small pieces for a total of 8 pieces 4 of each color. They should work each piece into a rounded shape the size of a green pea and place the pieces on the wax paper. 08. Read Part #3 from "The Rock Story." 09. The team should place six pieces of clay of one color in a layer on the wax paper three pieces by two pieces (like eggs in an egg carton). Students are now to layer another group of small pieces of clay on top of the first layer of sedimentary rock. Since this layer is made from different material the next layer should be made by a different color clay. Rock Cycle Gr. 4 Page 3
10. Students are to continue making layers of sedimentary rock until they have used up all the clay pieces. It is important to alternate colors as the layers stack up in order to convey the idea that different materials are settling. 11. Read Part #4 from "The Rock Story." 12. Using a plastic knife, the classroom teacher divides each team s sedimentary rock sample in half. Have students place one half on the section of the worksheet marked sedimentary where it will remain throughout the lesson. The remaining half is placed on the wax paper. 13. Students are to gently press down on the sedimentary sample remaining on the wax paper. 14. Read Part #5 from The Rock Story. 15. Instruct students to use a corner of the wax paper to cover the sedimentary rock sample. Have students press down on the sample to simulate the pressure and heat necessary to metamorphose the rock into a metamorphic rock. 16. Students should place the metamorphic rock sample on the section of the worksheet marked metamorphic. 17. Dispose of the wax paper. 18. Place the clay samples/worksheets somewhere in the room where students can use them for reference. CONCLUSION: 01. Ask the students: n How can a sedimentary rock to be formed from metamorphic rock? Rock Cycle Gr. 4 Page 4
n Is it possible for the Rock Cycle to work "in reverse?" Source: 01. MITS: Museum Institute For Teaching Science. Adapted from Science and Children, May 1985 Rock Cycle Gr. 4 Page 5
The Rock Story Part #1: Once upon a time millions of years ago there was a lump of magma deep inside the Earth. It was very hot, so hot that it was plastic-like clay. Because this lump of dough was less dense than the surrounding magma, it rose towards the surface of the earth like a bubble of gas in soda. As it rose, it traveled most easily through the weakest portions of the Earth's crust. Eventually it found its way to a place where the crust was already buckling to form mountains. The hot doughy magma filled in the places beneath the mountains as they rose, but it did not reach the surface. It was trapped many miles beneath the surface by layers of rock. Very slowly it began to cool. As it cooled, minerals began to crystallize out of it. The minerals were quartz, feldspar, hornblende and mica. The magma had become an igneous rock. Part #2: Many thousands of years passed. Rain fell; ice froze and melted many times. The dirt and rocks on top of the granite-cored mountains were being weathered by the elements and erosion was washing pieces down the Rock Cycle Gr. 4 Page 6
mountainside. The layers of rock that had kept the granite from reaching the surface were eroded away. Now the granite itself was exposed to the rain, ice and snow. It too began to weather. Rain washed into cracks and froze. The freezing water expanded and split off chunks of granite. These chucks rolled and bounced down the mountainsides, cracking and chipping into smaller and smaller pieces. The pieces became so small they became grains of sand. Part #3: They were washed into streams and rivers and carried many miles, nearly to the ocean. When the river water began to slow, the grains of sand settled to the bottom to form a soft, sandy riverbed. As the sand layer became deeper and deeper the grains were pressed together to form a sedimentary rock. Centuries pass. The sea level begins to rise. Many feet of seawater now cover what had once been the riverbed. Billions of sea creatures floated and swam in the saltwater above the old riverbed. When they died their skeletons and shells settled to the bottom. Tiny particles of silt and clay washed into the sea from rivers also settled to the bottom. Rock Cycle Gr. 4 Page 7
Part #4: Thousands of years passed. The sea level dropped again. Mountains rose. Tremendous forces pressed against the layers of sandstone, shale and limestone lifting and wrinkling them. In places the layers were even folded over on each other. Part #5: Heat and water from deep in the ground combined with tremendous pressure to change some of the minerals in the rocks so that they no longer looked the same. The rock now had many bands or thin stripes in it. It had become a metamorphic rock. Rock Cycle Gr. 4 Page 8