|Earth and Space Science||Structure Of The Earth 8I4.00||Unifying Concepts of Science||Change 2.5 b|
Sponsored by the National Science Foundation
CONTENT STANDARD: Earth and Space Science
CONTENT TOPIC: Structure Of The Earth
CONCEPT: Changes in the solid earth can be described as the rock cycle.
CONTENT OBJECTIVE: 8I4.00 To understand the rock cycle.
INSTRUCTIONAL OBJECTIVES: The learner will
TN COMPONENT OF SCIENCE: Unifying Concepts of Science
BENCHMARK: Sedimentary rock provide evidence for the long history of the earth.
BENCHMARK: Some changes in the earth's surface are abrupt while other changes happen very slowly.
Igneous rocks compose the majority of the rock in the earth's crust. They are formed from hardened liquid rock called magma. The magma may move upward because of great pressure, or it may flow out onto the surface of the earth.
The texture of igneous rocks is determined by the size of the grains. If the magma solidifies deep within the earth, the size of the crystals in the rock will be large due to slow cooling. These igneous rocks are classified as intrusives. Rocks that are formed during rapid cooling will produce fine crystals; these rocks are known as extrusives.
Igneous rocks are divided into five categories according to the minerals each type contains. The first is called granites which contain quartz, feldspar, and mica. The second group is called diorites. The diorites contain feldspar and one or more dark minerals with the feldspar being the dominant one. The third group is called the gabbros. This group contains feldspar and one or more dark minerals with the dark minerals being the dominant mineral. The next group is called the periodotites. These rocks are generally black or dark and contain iron. The last group is called the pegmatites. These rocks are coarse-grained granites with large crystals of quartz, feldspar and mica.
Sedimentary rocks are rocks that are exposed in a lot of areas; in fact, they cover about 75 percent of earth's surface. Any rock that has been exposed to the sun, rain, air, plants or animals undergoes a change. These changes break rock down into sediments. These sediments become buried and hardened into sedimentary rock.
There are five main types of sedimentary rock. The first type is called conglomerate. Conglomerates are made of pebbles or larger rocks cemented together. The second type is called sandstone. Sandstone is composed of sand grains which are cemented together. Shale is the third type of sedimentary rock. Shale is clay that has been converted into rock masses. The next group is called limestone. Limestone is generally composed of calcium carbonate, microscope shells, or both. The final group of sedimentary rocks is called gypsum or common salt or Epsom salt. These are compounds found in sea water that precipitate as the water evaporates.
Sedimentary rocks are usually formed in several layers called strata. The different layers can be recognized by color, composition or the grain size. In a group of several, the oldest bed is at the bottom and the youngest is found at the top. Fossils are important components found in many sedimentary layers. Fossils represent a record of past life because it is a bone, shell or even a body part. Limestone generally has many fossils while shale and sandstone generally have fewer.
Of the three kinds of rock, metamorphic rock is the least abundant. Metamorphic rock, unlike sedimentary and igneous rock forms only at great depths or in high temperatures. Usually metamorphic rock is formed at temperatures between 150C and 800C and at depths from one mile to several miles. It is believed that the heat originates with the decay of radioactive elements and the pressure results from the weight of sediments lying above or from all the forces that accompany mountain building. Metamorphic rocks are divided into groups depending on whether or not they have bands. Foliated rocks have banding, non-foliated do not. The first group of foliated rocks is call slates. Slate splits into smooth slabs. It is mostly blue-black but it may also be black, red and green. Schists are the most common metamorphic rocks; mica is the most common mineral. Gneiss is another group of metamorphic rocks. It has a streaky appearance due to alternating layers of minerals.
Non-foliated metamorphic rocks include the group marble. Marble can be fine or coarse. It can also be scratched by a knife and bubbles when put into acid. The last group of metamorphic rocks is called quartzite. Quartzite is the hardest and most resistant rock.
All three types of rocks form the rock cycle because anyone of the three can help to form either of the other two groups. This is illustrated by the cycle given below.
2. Let the students help you make fudge. Put part in a pan and let cool at room temp. Put the other half in the refrigerator until hardened. Compare the textures of the 2 kinds of fudge. Compare these textures to intrusive and extrusive rocks.
Cook slowly until it reaches 234oF or until it forms a soft ball when dropped into cold water. Remove from heat and add 2 tbsp. of butter.
3. Mix different combinations of sand, gravel, clay, plaster, and water. Use just enough water to make a stiff mixture. Put all the containers in an oven at 200oF. Turn off the oven. Let the mixtures set until all the H2O has evaporated. Compare these samples of sedimentary rock. (Be sure to have 3 control groups)
a. clay, plaster + H2O
b. sand, plaster + H2O
c. clay, plaster + H2O
d. any combinations of above
4. Have students examine examples of metamorphic rock. Have them to classify the rocks into groups labeled foliated and non-foliated. Test each sample with a few drops of hydrochloric acid (HCl) what happens?
2. Organic-contains carbon and/or hydrogen
3. intrusive-igneous rocks which contain large crystals
4. Extrusive-igneous rocks which contain small crystals
5. Strata-layers of rock
6. Foliated rocks-rocks with bands of different colors or kinds of rock
7. non-foliated rocks-rocks without bands
This is the time this file has been accessed since 04/04/98.
The University of Tennessee at Martin is not responsible for the information or views expressed here.
Eighth Grade Science Home Page