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Applying Density to Earth (2 Favorites)

ACTIVITY in Density, Elements, Interdisciplinary. Last updated October 21, 2019.


Summary

In this activity, students will analyze data related to elevation and rock composition, in order to better understand the impact that density has on earth chemistry.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

  • HS-ESS1-6: Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth’s formation and early history.
  • HS-ESS2-3: Develop a model based on evidence of Earth’s interior to describe the cycling of matter by thermal convection.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data
    • Engaging in Argument from Evidence

Objectives

By the end of this activity, students should be able to

  • Interpret and analyze data that is provided both visually, and quantitatively.
  • Explain the relationship between elements, minerals and rocks.
  • Compare and contrast the composition of basalt and granite.
  • Describe how density is important to the study of earth chemistry.

Chemistry Topics

This activity supports students’ understanding of

  • Earth Chemistry
  • Density
  • Elements
  • Compounds
  • Minerals

Time

Teacher Preparation: 10 minutes

Lesson: 30-45 minutes

Materials

  • Computer/Device with Internet access
  • Student handout

Safety

  • No specific safety precautions need to be observed for this activity.

Teacher Notes

For the Student

Lesson

Background

Humans don't live in the oceans. Humans on the continents. If the entire Earth was covered by water, humans probably would not have evolved as they have. So what has provided us with continents on Earth?

  1. Earth as we see it has ocean areas and land areas. But, what would a completely dry Earth look like if all the water was gone?The map image below shows elevations on Earth with all the water removed - note these elevations exist whether there are oceans or not.

  1. a. Are elevations evenly distributed from high to low, or does it seem like there is a lot of high (red) and a lot of low (green), but not as much in the middle (yellow)?
  2. b. Also, looking at the yellow around the red, does it seem like there is relatively small amount of land in the transition from red to green?
  1. The two main elevations in image above exist regardless of water on the planet.
    1. However, why are we not usually aware of the lower land that is green in this map?
    2. What happens to water when it rains, especially on the red elevations, that makes this so?

    1. Knowing this fact about the Earth, what questions would you have?
    2. If you wanted to answer those questions, what other questions might you need to ask to get enough data to come up with an explanation?
  1. As a basic concept, elements combine to make minerals as naturally occurring compounds, and minerals then aggregate together physically to make rocks. There are three major classes (groups) of rocks, do you remember what they are from previous science classes?
  2. We can characterize the composition of much of Earth's crust by the names of the igneous rocks that match the crustal composition. In the map image, the red areas and nearby yellow areas generally are the composition of the igneous rock granite, while the green areas and enclosed (mid-ocean) yellow areas are generally the composition of the igneous rock basalt. You can find these rock names outlined in red in the chart below. The areas within the red outline shows mineral names and relative amounts of the mineral composition of these rocks.
    1. What minerals do you find in granite?
    2. What minerals in basalt?

  1. The mineral compositions you found in the previous question affect the chemical properties of these rocks. One property you have studied, density, is important here, along with the understanding that lower density materials can float on higher density materials. For Earth, there is a layer under the crust called the asthenosphere that is solid but deformable (peanut butter is a similar deformable solid but the layer in the Earth is much more solid), so less-dense layers of the crust can float on this moveable solid layer. So then the densities of the granite and basalt crust become important because that will determine how these areas float on the asthenosphere.
    1. Examine the data in the table below. Note that the minerals, their densities and percent abundance are presented and use to calculate overall densities for granite and basalt.
    2. Which rock is more dense, granite or basalt?
    3. If both are floating on the deformable asthenosphere, which will float higher?
Mineral Mafic or felsic silicate? Density in g/cc Minerals %in an examplegranitic sample Granite density g/cc Minerals % in an example basaltic sample Basalt density g/cc
K feldspar - orthoclase felsic 2.56 30% 0.77 * *
quartz felsic 2.65 30% 0.80 * *
Na plagioclase - albite felsic 2.62 30% 0.79 * *
muscovite felsic 2.82 5% 0.14 * *
biotite mafic 3.1 5% 0.16 * *
amphibole - hornblende mafic 3.15 * * 10% 0.32
Ca plagioclase - anorthite mafic 2.73 * * 55% 1.50
pyroxene - augite mafic 3.4 * * 30% 1.02
olivine mafic 3.77 * * 5% 0.19
Sums 100% 2.65 100% 3.03
  1. It's also true that granite crust is usually thicker than basalt crust. Putting all these facts together, draw your conclusion about why Earth has two main levels of elevation, and state your evidence and reasoning. Why is this chemistry important to life on Earth?
  2. We have looked at density of the outer layers of rock on Earth. Expanding our view, examine the image below and look for a pattern.
    1. How do the densities of major Earth materials vary from the center of the planet to the atmosphere?
    2. Does this help you see why you have studied density in chemistry class?