Earth Science Lab
Lab # 24
Name ________________________________________________
Due Date ____________________________________________
Crustal Density
Introduction: The Earth's Crust is like the skin of an apple. It is very thin in comparison to the
other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans(oceanic
crust) and about 25 miles (32 kilometers) thick under the continents (continental crust).
The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, plastic
mantle which is located below the crust. These plates usually move along smoothly but sometimes
they stick and build up pressure. The pressure builds and the rock bends until it snaps. When this
occurs an Earthquake is the result! Notice in the picture above how thin the crust of the Earth is in
comparison to the other layers. The seven continents and ocean plates basically float across the
mantle which is composed of much hotter and denser material.
In this activity you will measure the density of the rock making up the continental crust and
oceanic crust. Continental crust is made of the rock granite and oceanic crust is made of basalt.
Method:
 Measure the mass of each rock sample in grams and record them in the data table.
 Measure the volume of each rock sample in cubic centimeters (cm3) and record them in the
table.
 Using your measurements, calculate the density of each rock. Show your work in the space
provided in the data table.
Follow-Up Questions:
1. Which kind of crust has a higher density? Be sure to support your answer with data.
2. What rock group is the continental and oceanic crust made of? Name an observable
characteristic for these rocks.
3. The crust is broken into tectonic plates. When plates collide they can subduct. Which crustal
material will subduct during convergence? Why?
Data Table:
Mass (g)
Volume (cm3)
Density (g/cm3)
(show work)
Granite
Basalt
Conclusion: Why are the surface of the continents found at a higher elevation that the surface of the
ocean floor?