Download Earth Materials, Processes and Isostasy

Before lab: read sections 1.9 & 1.10, p. 27-30 of Chapter 1 in your lecture textbook.
L aboratory 1: E xamining E arth materials and processes
M aterials needed: pencil, eraser, metric ruler, graduated cylinders, rock and mineral
samples, water, wood blocks, balance, wash bottle and calculator, your lab manual.
O bjectives:
1. Measure or calculate volume, mass and density of Earth materials using basic
scientific equipment and techniques (density = mass/volume). (Density = !)
2. Make relative comparisons of the densities of common earth materials and
YDULRXVSDUWVRIWKH(DUWK¶VV\VWHPV
3. Develop and test physical and quantitative models of isostasy based on floating
wood blocks. Then apply your quantitative model and measurements of basalt
and granite density to calculate the isostasy of average blocks of oceanic and
continental crust.
Part I: Volume, M ass, and Density Determinations
1.
a. Explain how to determine the density of water ( ! water) in g/cm3 using only a
small graduated cylinder and a balance.
E&DOFXODWHWKHGHQVLW\RIZDWHUXVLQJWKHWHFKQLTXH\RX¶YHGHYHORSHG
2.
Using the technique that you developed, calculate the densities (in g/cm3) for the
following earth materials (*Note: make sure to calculate their volumes as
accurately as possible ± to the nearest tenth of a ml):
a. The coarse-grained red colored rock
b. The fine-grained black colored rock
c. The metallic-looking mineral
!
Part I I: Relative Comparisons with E arth M aterials
Make a relative comparison of the densities of various parts of the Earth to the densities
of samples a-c (above) by completing the following statements: Use terms: More, Less, or Equal
3. D7KH(DUWK¶VDWPRVSKHUHLVBBBBBBGHQVHWKDQWKHFRDUVH-grained red colored rock
E7KH(DUWK¶VDWPRVSKHUHLVBBBBBBGHQVHWKDQWKHILQH-grained black colored rock
F7KH(DUWK¶VDWPRVSKHUHLVBBBBBBGHQVHWKDQWKHPHWDOOLF-looking mineral
4. Ocean density is ~ 1.03g/cm3
D7KH(DUWK¶VRFHDQLVBBBBBBGHQVHWKDQWKHFRDUVH-grained red colored rock
E7KH(DUWK¶VRFHDQLVBBBBBBGHQVHWKDQWKHILQH-grained black colored rock
F7KH(DUWK¶VRFHDQLVBBBBBBGHQVHWKDQWKHPHWDOOLF-looking mineral
5. Continental crust density is ~ 2.4 ± 2.69 g/cm3
a. Continental crust is ______ dense than the coarse-grained red colored rock
b. Continental crust is ______ dense than the fine-grained black colored rock
c. Continental crust is ______ dense than the metallic-looking mineral
6. Ocean crust density is ~ 2.7 ± 3.2 g/cm3
a. Ocean crust is ______ dense than the coarse-grained red colored rock
b. Ocean crust is ______ dense than the fine-grained black colored rock
c. Ocean crust is ______ dense than the metallic-looking mineral
7. Upper mantle density is ~ 3.3 g/cm3
a. Upper mantle is ______ dense than the coarse-grained red colored rock
b. Upper mantle is ______ dense than the fine-grained black colored rock
c. Upper mantle is ______ dense than the metallic-looking mineral
8. Average Earth density is ~ 4.4 ± 5.5 g/cm3
a. The Earth as a whole is ______ dense than the coarse-grained red colored rock
b. The Earth as a whole is ______ dense than the fine-grained dark colored rock
c. The Earth as a whole is ______ dense than the metallic-looking mineral
!
Part I I I: Isostasy
9. The general equation for determining the density of an object that floats in a fluid
(such as water) is expressed as:
H below =
where:
! object
____________ H total
! fluid
H below = height of object below water (or whatever fluid the object is
floating in)
H total = total height of floating object
! object = density of floating object
! fluid = density of fluid the object is floating in (e.g. water)
a. Calculate the density of the block of wood block provided to you using a ruler
and the electronic scale at the front of the table. Show your calculations.
b. Now calculate the density of the block a second time (ignoring your answer to a),
but this time use the equation provided above, a ruler, and the buckets of water in
the sinks at the end of your lab table. Show your calculations.
*Hint: you will have to rearrange the equation to solve for !object
c. Discuss if the densities you calculated using the two methods are similar or
different, and why they are the same or different.
10.The density of a typical iceberg is 0.917 g/cm3, whereas the average density of ocean
water is 1.025 g/cm3 (Busch, 2003). Use the isostasy equation given in Question 9 to
determine what percentage of an iceberg occurs below sea level. Show your work.
!
11. Density measurements of individual pieces of granite from throughout the world
yield the following results:
Sample Number Density (g/cm3) Sample Number Density (g/cm3)
1
2
3
4
5
2.6
2.8
2.9
2.9
2.8
6
7
8
9
2.8
2.7
2.8
2.8
Using the information above AND the density you calculated for the red rock
(question 2a), calculate the average density of granite.
12. Density measurements of individual pieces of basalt from the seafloor yield the
following results:
Sample Number Density (g/cm3) Sample Number Density (g/cm3)
1
2
3
4
5
3.0
3.0
3.2
3.1
3.1
6
7
8
9
3.0
3.2
3.1
3.1
Using the information above AND the density you calculated for the black rock
(question 2b), calculate the average density of basalt obtained from the seafloor.
3HULGRWLWHLVDW\SHRIURFNWKDWPDNHVXSWKHHDUWK¶Vasthenosphere (upper mantle).
It has a density of 3.3 g/cm3. Use this information along with the equation on the
previous page to answer questions a and b.
a. The average thickness of the granitic continental crust is about 30 km. Use the
average density of granite you calculated in problem 11 to determine how high (in
kilometers) granitic crust floats above the mantle. Show your work.
b. The average thickness of the basaltic oceanic crust is about 5 km. Use the average
density of basalt you calculated in problem 12 to determine how high (in
kilometers) basaltic crust floats above the mantle. Show your work.
!
c. What is the difference (in kilometers) between your answers for questions 13a
and 13b?
d. Detailed measurements indicate that the difference between the average
continental elevation and the average oceanic basin is ~4.7 kilometers. How does
your answer for question 13c compare to this number?
e. Based on your analysis, discuss (in a complete sentence) why the average
continental crust floats ~4.7 km higher than the average oceanic crust.
!
!
!
!
¨Please get a key from your instructor and self-cor rect your lab.
¨T hen show your lab to your instructor for attendance credit.
!