Download Density of the Earth

Lab: Density of the Earth
Overview:
The mass of the earth is approximately 5.98 x 1023kg. The scale of this measurement is difficult to
comprehend and impossible to measure directly. However, smaller scale measurements can be completed in the
laboratory that will give insight into the density and mass of the Earth.
Current theories of the beginning of our solar system suggest that the early chemical composition of the
solar system may still be preserved in solid remains such as comets and meteors. Comets, of course, are much
more difficult to test directly than meteorites – having entered the Earth’s atmosphere; meteorites are actually
found on earth after entering Earth’s atmosphere. By studying these objects directly and indirectly and then
studying the characteristics of Earth via seismic waves, scientists can calculate the density of the planet. Earth’s
size and gravitational field yield clues about the “guts” of the Earth – the materials and their densities that make
up the structures of Earth beneath the lithosphere. The average density of the Earth has been calculated to be
5.5 g/cm3.
Pre-Lab Questions:
 Lithosphere: _________________________________________________________________________
 Asthenosphere: ______________________________________________________________________
 What are the three rock types? ___________________________________________________
PART A – What is the difference between continental and oceanic crust?
There are all sorts of rocks in the earth’s crust. The two main examples in the crust are granite and basalt. Your
goal is to determine which of the two rocks would make up most of the continental crust and which would make
up most of the oceanic crust.
Data Collection Follow the Density Lab procedures for both rock examples: Basalt & Granite.
Procedure:
Part A – Data Collection
1. Obtain a container with 3 pieces of Basalt or Granite.
2. Make sure they are DRY before you begin!
3. Using a balance, find the mass of each of the 3 samples to the nearest tenth of a gram. RECORD the
masses.
4. Obtain a graduated cylinder and fill it halfway with water. RECORD starting height of water.
5. Gently, drop your 1st sample into the graduated cylinder. If the water does not completely cover your
sample, take the rock out of the graduated cylinder, add more water and start over at step 4. RECORD
final height of water with sample.
6. Subtract (final height of water with sample – starting height of water). RECORD volume of sample.
7. Calculate the density for sample #1. (D = Mass / Volume)
8. Pour out water into “waste water” bucket and retrieve used sample. Put the sample back.
9. Repeat steps 4-8 with sample pieces 2 & 3.
10. Calculate and Record the Average Density for your three samples.
11. Repeat entire procedure list above with either Basalt or Granite (whichever you didn’t do already…)
Part A – Analysis Questions:
The less dense portions of the Earth’s crust rise (lower or higher) on the asthenosphere. These portions
are called continental crust. These portions of Earth’s crust are thick, and composed mostly of larger
crystal grains. They have a (smaller or higher) density. The rock most commonly found here is (basalt
or granite).
The more dense portions of the Earth’s crust rest (lower or higher) on the asthenosphere. These portions
are called oceanic crust. They have a (smaller or higher) density and sit lower in elevation. The rock
most commonly found here is (basalt or granite).
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PART B: What is the difference between rock types?
There are three main rock types: igneous rock, sedimentary rock, and metamorphic rock. How do these rock
types compare with each other and do they represent the density of the whole Earth?
Data Collection Follow the Density Lab procedures for the sedimentary and metamorphic rock samples.
Procedure:
Part B – Data Collection
1. Obtain a container with 3 pieces of one of these: Limestone, Sandstone, Slate, Gneiss.
2. Make sure they are DRY before you begin!
3. Using a balance, find the mass of each of the 3 samples to the nearest tenth of a gram. RECORD.
4. Obtain a graduated cylinder and fill it halfway with water. RECORD starting height of water.
5. Gently, drop your 1st sample into the graduated cylinder. If the water does not completely cover your
sample, take the rock out of the graduated cylinder, add more water and start over at step 4. RECORD
final height of water with sample.
6. Subtract (final height of water with sample – starting height of water). RECORD volume of sample.
7. Calculate the density for sample #1. (D = Mass / Volume)
8. Pour out water into “waste water” bucket and retrieve used sample. Put the sample back.
9. Repeat steps 4-8 with sample pieces 2 & 3.
10. Calculate and Record the Average Density for your three samples.
11. Repeat entire procedure list above with either: Limestone, Sandstone, Slate, Gneiss. (whichever you didn’t do already…)
Data Analysis:
1. All the rock samples in Part A and Part B are a sample of the Earth’s lithosphere. Average all of these
densities to get an estimate for the Earth’s lithosphere. Show your work and RECORD on the bottom
of the data table page.
Part B – Analysis Questions:
1. (Sedimentary/Metamorphic/Igneous) rocks are the most dense.
2. (Sedimentary/Metamorphic/Igneous) rocks are the least dense.
3. The average density of Earth is 5.5 g/cm3. We calculated the average density of the Earth’s
lithosphere is much (lower/higher) than the actual average density of the entire Earth. The density
of the core of the Earth should be (much higher/a little bit higher/a little bit lower/much lower) than
that of the lithosphere.
Data Table:
Sample Type
Mass (g)
Granite
(igneous)
Basalt
(igneous)
Limestone
(sedimentary)
Sandstone
(sedimentary)
Slate
(metamorphic)
Gneiss
(metamorphic)
Average Density of all rock samples:
Work=
Answer= __________g/mL
Volume (mL)
Density
Average Density