Name: _________________________________ Date:_______________ Period:____
EARTH SCIENCE Density: Continental High, Ocean Low Basalt and Granite Saul 2013
Focus Question: Which has a greater density: Basalt or Granite?
Background : The Earth is heterogeneously layered into 3 basic parts: the crust, the mantle and the core.
Scientists believe that differences in the physical property of density are responsible for the layering of the Earth with the densest layers toward the center of the Earth and the least dense layers found at the surface of the planet. The core is believed to be composed of iron and nickel, which are two very dense metals. The crust is the outer most layer of the Earth and is divided into two parts, the oceanic crust and the continental crust. Ocean crust is made mostly of iron-rich igneous rock known as basalt.
Continental crust i s mostly composed of silica-rich igneous rock called granite .
Image 1
Key Vocabulary:
Crust:
Ocean Crust:
Basalt:
Continental Crust:
Granite:
Mass:
- The unit of measurement for mass is the (g)
Volume:
- The unit of measurement for volume is the (ml) or cm 3.)
Density :
The formula for calculating density is
The unit of measurement for density is or
Purpose:
In this activity we will determine the experimental density of basalt and granite, the rocks that make up the ocean crust and the continental crust.
Refer to the background information and image 1 above to help you hypothesize.
Hypothesis: I think the density of the oceanic crust will be (more or less) than the density of the continental crust because

Procedure:
1. Use the triple beam balance to find the mass (g) of each rock then record in Table 1 or 2.
2. Practice the Water Displacement Method to obtain the volume of the rock by pouring water from the beaker into the graduated cylinder to the ______ mL line.
3. Gently tip the graduated cylinder slightly and slide the rock into the graduated cylinder
4. Record the volume of the rock + water in the data table
5. Calculate the volume of the rock only by subtracting the start volume from the volume of the water & the rock.
6. Pour the water back into the beaker and remove the rock.
7.
Find the rock’s density by dividing the Mass of Rock by the Volume of Rock.
Density Formula: D=M/V
Results:
Rock
Name
Basalt 1
Basalt 2
Mass (g)
Average Density of OCEAN Crust (Basalt)
Start Volume
(ml)
Volume of
Water &
Rock (ml)
Volume of rock ONLY
(ml)
Density of
Rock g/cm3
Average
Density g/cm3
Basalt 3
Basalt 4
Basalt 5
Basalt 6
Table 1
Rock
Name
Granite 1
Mass (g)
Average Density of CONTINENTAL Crust (Granite)
Start Volume
(ml)
Volume of
Water &
Rock (ml)
Volume of rock ONLY
(ml)
Density of
Rock g/cm3
Average
Density g/cm3
Granite 2
Granite 3
Granite 4
Granite 5
Granite 6
Table 2

Results
GRAPH
Create an appropriate graph to represents the AVERAGE density values for Granite (Continental Crust) and Basalt (Oceanic Crust). Use the G-TAILS+S format to guide you.

Data Analysis/ Conclusion Questions:
REFER to the AVERAGE Densities to answer the questions in complete sentences.
1. What is the experimental average density of basalt, which makes up the ocean crust?
2. What is the experimental average density of granite, which makes up the continental crust?
3. Was your hypothesis supported by the outcome of the experiment? Explain by citing or writing about the specific experimental data to justify and support your answer.
4. By carrying out experiments similar to the one you just performed, scientists have determined the true average density of basalt (ocean crust) to be 3.0 g/cm3 and the true average density of granite (continental crust) to be about 2.7 g/cm3 .

Examine your experimental average densities and the true density values of granite and basalt. How are they similar and/or different?

Discuss at least 2 possible sources of error that could account for any inaccuracies or differences between the true density values and the experimental density values.
5. Use the background information and specific data from this investigation to explain why the thinner ocean crust sits lower than the thicker continental crust.
6. Make a prediction: How might the density values for the mantle and the core contrast to the density values of the oceanic and continental crust? (Do you think their density values would be similar or different?) Explain /support your reasoning.
7. During this activity, each group conducted only 1 trial, but as a class we conducted 6 trials and then found an average. Explain why it is important for scientists to conduct multiple trials in a scientific investigation?