Name: ______________________________________________ Date:_______________ Period:____
EARTH SCIENCE
Subduction and Density: Basalt and Granite
Which has greater density: Basalt or Granite?
BACKGROUND
A plate boundary is where two plates meet. When two plates move towards each other they form what is
called a convergent boundary.
Ocean crust is made mostly of iron-rich rock known as basalt. Continental crust is mostly composed of
silica-rich rock called granite.
When an ocean plate and a continental plate meet at a convergent boundary, one plate moves under the
other in a process called subduction. At a subduction zone, the plate that sinks returns to the mantle
where it heats, melts, and forms magma.
In this lab we will test the density of the rock that makes up the ocean crust and the continental crust. The
denser crust moves beneath and melts at a subduction zone.
INSTRUCTIONS
1. Use the beaker to measure 1500mL (3 x 500) of water.
2. Pour water from the beaker into the tray.
3. Slide the items labeled Oceanic Plate and Continental Plate into the graduated tray.
4. Using the ruler, measure from the bottom of the tray to the top of each plate.
5. Record the height of the oceanic plate in the Basalt row.
6. Record the height of the continental plate in the Granite row.
7. When everyone in your group has done steps 4 & 5 three times remove the items, pour the water
back into the bucket and use a paper towel to wipe out the tray, dry the items and clean the table if
needed
8. Work with your learning team to average your results. Remember, to average you total all the
results in a column and divide them by the number of trials.
OCEANANIC PLATE
Basalt 1
Basalt 2
Basalt 3
Granite 1
Granite 2
Granite 3
NAME:
NAME:
NAME:
NAME:
AVERAGE
CONTINENTAL PLATE
Name:
Name:
Name:
Name:
AVERAGE
CLASS DATA:
Trial #
1
2
3
average
Group 1
OCEAN CRUST -- BASALT
Group 2 Group 3
Group 4
Group 5
Group 6
Group 7 Group 8
Trial #
1
2
3
average
Group 1
CONTINENTAL CRUST -- QUARTZ
Group 2 Group 3
Group 4
Group 5
Group 6
Group 7 Group 8
QUESTIONS
1. What is the average height of basalt, which makes up the ocean plate? ______________
2. What is the average height of granite, which makes up the continental plate? __________
3. What, if any, possible sources of error could account for unusual results?
____________________________________________________________________________
____________________________________________________________________________
4. By comparing the class averages, I found that the ____________________________ had a greater
density than the ____________________________.
By carrying out experiments similar to the one you just performed, scientists have determined the density
of basalt (ocean crust) to be 3.0 g/mL and the density of granite (continental crust) to be
about 2.7 g/mL.
5. Based on this information, which plate would sink at a convergent boundary where an ocean plate
meets a continental plate?