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Label and color the layers of the Earth’s interior.

Use google Earth to examine the shape of the continents and the trend of the Hawaiian islands to see how these relate to the Theory of Plate Tectonics.

Calculate the rates of plate motion and density of continental and oceanic crustal rocks.

Create a concept sketch of the different types of plate boundaries and use Google Earth to locate plate boundaries and surface feature.

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LAB 3: PLATE TECTONICS
Activity 3A: Rates of Change
One of the most important equations we will use in this course is the “dirt” equation:
Distance = Rate x Time (read as distance equals rate times time)
When you know two of the variables in this equation, you can figure out the third. We can
move the variables around in the equation to suit our needs (but then we couldn’t call it the
“dirt” equation):
Rate = Distance/Time (read as rate equals distance divided by time)
or
Time = Distance/Rate (time equals distance divided by rate)
Example: Car Speed
It’s summertime: you decide to go on a road trip. You want to figure out how long it will take
you to drive to the Grand Canyon. You look on your map app and see that you are 380 miles
away… when suddenly, your phone dies! Assuming you will drive at an average rate of 60 mph,
how many hours will it take you to drive to the Grand Canyon?
First, write down your known variables:
Distance =
Rate =
Then, calculate your unknown variable using one of the equations above. Show your work:
Time =
Geology Example: Rate of Sedimentation
While you’re out hiking, you encounter an interesting-looking rock bed. You can tell by the
pebbles incorporated throughout the rock bed that it was laid down by a river over a long time.
You want to find out how fast the bed was deposited by the river (this is called rate of
sedimentation).
You measure how thick the bed is (this is its distance, a measurement of length) and discover it
is 1.8 meters from the base to the top. Luckily, this bed is sandwiched by two ash beds laid
down by volcanic eruptions: ash can be dated by radiometric dating!
After analyzing the samples in a lab, you learn the lower ash bed is dated at 10.1278 Ma (read
as million years old) and the upper ash bed is dated at 10.1251 Ma.
Figure 3.1: Outcrop of layers of sedimentary rock and ash. The ash layers have been
radiometrically dated.
What is the average rate of sediment deposition for your rock bed?
Write down your known variables:
Distance (Length, width, or thickness) =
Time =
Then, calculate your unknown variable. Show your work:
Rate =
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Activity 3B: Plate Motion and Evidence
One of the most striking things about the geography of the continents today is how they appear
to fit together like puzzle pieces. The reason for this is clear: they once were connected in the
past and have since separated shifting into their current positions.
Use GoogleEarth Pro or open the browser version of Google Earth and zoom out to an eye
altitude (camera) of ~10,000 miles. Examine the coastlines of eastern South America and
Western Africa and notice how well they match in shape. There are scientifically important rock
deposits in southern Brazil, South America and Angola, Africa that show the northernmost
glacial deposits on the ancient continent of Pangaea, which indicates these two areas were
once connected.
1. Based on the shape of the two coastlines, give the present-day latitude and longitude of
two sites along the coasts of these countries that used to be connected when the two
continents were joined as a part of Pangaea (note: there are multiple correct answers):
a. Brazil:
i.
Latitude:
ii.
Longitude:
b. Angola
i.
Latitude:
ii.
Longitude:
2. Measure in centimeters the distance (Map Length) between the two points you
recorded in the previous question. Hint: use the ruler icon (left or top toolbar).
a. Distance (in centimeters) =
3. This portion of Pangaea broke apart 200,000,000 years ago. Using the distance you
measured above, calculate how fast (the rate) South America and Africa are separating
in cm/year. (Hint: the formula to use here is Rate= Distance/Time). SHOW YOUR WORK.
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Examine the Western Coast of South America, the Eastern Coast of Asia, and the Pacific Ocean.
If South America and Africa are separating and the Atlantic Ocean is growing, then the opposite
must be occurring on the other side of the earth (the Americas are getting closer to Asia and
the Pacific Ocean is shrinking). It begs the question, when will the next supercontinent form? To
determine this, we need a bit more information.
4. Measure the distance between North America and Mainland Asia in centimeters? (Hint:
measure across the Pacific at 40° N latitude, between Northern California and North
Korea)
a. Distance (in centimeters) =?
5. Using the distance above, and the rate calculated in question 3, determine the time it
will take to develop a new supercontinent. (Hint: the formula Rate= Distance/Time, can
be reworked to Time = Distance/Rate). SHOW YOUR WORK.
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Activity 3C: The Structure of Internal Earth
Label each layer at their correct letter, then color the layers using the following colors:
â—‹
â—‹
â—‹
â—‹
Asthenosphere – Light green
Continental crust – yellow
Inner core – red
Lithosphere – gray
â—‹ Mantle – label, but do not color
â—‹ Mesosphere – dark green
â—‹ Oceanic crust – black
â—‹ Outer core – orange
Figure 3.2: A cross-section of Earth to label.
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Activity 3D: Hot Spots
What Are Hot Spots?
In addition to GPS technology, geologists can also track plate motion using the location of hot
spots, volcanically active areas on the Earth’s surface that are caused by anomalously hot
mantle rocks underneath (Figure 3.3). This heat is the result of a mantle plume that rises from
deep in the mantle toward the surface resulting in the production of magma and volcanoes.
These mantle plumes occur within the asthenosphere or deeper, such that they are unaffected
by the movement of the continental or oceanic plates. Mantle plumes appear to be stationary
through time; therefore, as the tectonic plate moves over the hot spot, a linear chain of
volcanoes is produced. This gives geologists a wonderful view of the movement of a plate
through time with the distribution of volcanoes indicating the direction of motion and their
ages revealing the rate at which the plate was moving. Interested in hot spots? Want to learn
more? Read this article from Earth Magazine: The Question of Mantle Plumes.
Figure 3.3: The life of an oceanic hot spot.
The Hawaiian Hot Spot
One of the most striking examples of a hot spot is underneath Hawaii. The mantle plume
generates magma that results in an active volcano on the seafloor, referred to as a seamount.
Each eruption causes the volcano to grow until it eventually breaks the surface of the ocean
and forms a volcanic island. As the oceanic plate shifts the volcano off the stationary hot spot,
the volcano loses its source for magma and becomes inactive. The volcano then cools down,
contracts, erodes, sinks slowly beneath the ocean surface, and is carried by the tectonic plate as
it moves over time. As each island moves away from the mantle plume, a new island will then
be formed at the hot spot in a continual conveyor belt of islands. Therefore, the scars of ancient
volcanic islands near Hawaii give a wonderful view of the movement of the tectonic plate
beneath the Pacific Ocean.
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Use GoogleEarth Pro or open the browser version of Google Earth and type “Hawaii” into the
search bar and zoom out to an eye altitude (Camera) of 700 miles. Examine the chain of
Hawaiian Islands.
1. On the map of the Hawaiian Islands (Figure 3.4), include the following:
● A North arrow
● Label the following islands: Big Island of Hawaii, Kauai, Maui, Molokai, Oahu
Figure 3.4: Map view of the Hawaiian Islands.
2. Next, label on the map the ages of each of the islands. These ages were determined
through radiometric dating of the lava flows on the islands.
● Big Island of Hawaii: 0 years old (Active)
● Kauai: 5.1 million years old
● Maui: 1.3 million years old
● Molokai: 1.8 million years old
● Oahu: 3.7 million years old
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3. In Google Earth, measure the distance between the islands. To do this, measure from
the center of each island and its adjacent island in centimeters. (Hint: numbers will be
large)
a. Distance between the Big Island and Maui (in cm):
b. Distance between Maui and Molokai (in cm):
c. Distance between Molokai and Oahu (in cm):
d. Distance between Oahu and Kauai (in cm):
4. Look closely at each island in Google Earth and record the maximum elevation in
centimeters. (Hint: elevation can be determined by placing your cursor over a point and
reading the elevation on the lower right of the image by the latitude and longitude. The
elevation units can be changed in your settings. To locate the highest point on the
islands, tilt the image or use the 3D button. Convert meters to centimeters by multiplying
by 100.)
a. Big Island of Hawaii, max elevation (in cm):
b. Kauai, max elevation (in cm):
c. Maui, max elevation (in cm):
d. Molokai, max elevation (in cm):
e. Oahu, max elevation (in cm):
5. Consider the ages and positions of the islands listed above along with what you know
about plate tectonics and hotspots. In what general direction is the Pacific Plate
moving?
a. Northwest
b. Southeast
c. Northeast
d. Southwest
6. How fast was the Pacific plate moving during the last 1.3 million years between the
formation of the Big Island and Maui? Calculate your answer in cm/year. (Hint: Rate =
Distance/Time). SHOW YOUR WORK.
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7. How fast was the Pacific plate moving between the formation of Oahu and Kauai?
Calculate your answer in cm/year. (Hint: Rate = Distance/Time). SHOW YOUR WORK.
8. Zoom out and examine the dozens of sunken volcanoes, referred to as extinct
seamounts, to the northwest of Niihau, these are named the Emperor Seamounts. As
one of these volcanic islands on the Pacific Plate moves off the hotspot it becomes
inactive, or extinct, and the island begins to sink as it and the surrounding tectonic plate
cool down. The speed the islands are sinking can be estimated by measuring the
difference in elevation between two islands and dividing by the difference in their ages.
Note, this method assumes the islands were a similar size when they were active.
a. Calculate how fast the Hawaiian Islands are sinking, by using the ages and
elevations of Maui and Kauai. (Hint: Rate = Distance/Time). SHOW YOUR WORK.
b. When will the Big Island of Hawaii sink below the surface of the ocean? (Hint:
use the rate calculated above, ignoring possible changes in sea level, and the
max elevation of the Big Island in centimeters; Time = Distance/ Rate). SHOW
YOUR WORK.
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Activity 3E: Plate Densities
An important property of geological plates is their density. Remember the asthenosphere has
fluid-like properties, such that tectonic plates ‘float’ relative to their density. This property is
called isostasy and represents the equilibrium between crustal height and relative density. This
is similar to buoyancy in water. For example, if a cargo ship has a full load of goods it will
appear lower than if it were empty because the density of the ship is on average higher.
Therefore, the relative density of two plates can control how they interact at a boundary and
the types of geological features found along the border between the two plates.
Recall the Earth’s crust is divided into two main types:
● Continental crust, which is composed of granite, is relatively older and thicker than oceanic
crust. The thickness of the continental crust is between 25-70 km with an average thickness
around 30 km. The average density of granite is 2.75 g/cm3 (read as 2.75 grams per cubic
centimeter).
● Oceanic crust, which is composed of basalt, is relatively younger and thinner than
continental crust. The thickness of the oceanic crust is between 5-10 km with an average
thickness of 7 km. The average density of basalt is 3.0 g/cm3 (read as 3.0 grams per cubic
centimeter).
1. Which crustal type is thicker?
2. Which crustal type is denser?
a. How did you determine which crustal type was denser?
b. Why do you think this is the case?
3. Which crustal type is more buoyant?
a. How did you determine this?
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Measuring the density of rocks is fairly easy and can be done by first weighing the rocks and
then calculating their volume. The latter is best done by a method called fluid displacement
using a graduated cylinder. Water is added to the cylinder and the level is recorded, a rock is
then added to the cylinder and the difference in water levels equals the volume of the rock.
Density is then calculated as the mass divided by the volume (Density = Mass/Volume).
Figure 3.5 contains the information needed to calculate density. There are four rocks which
have weight (in grams) as well as the volume of water recorded by a graduated cylinder (in
milliliters) before and after the rock was added.
Notes:
● Each line on the graduated cylinder represents 10 milliliter (ml).
● When measuring volume, round to the nearest 10 ml line on the graduated cylinder.
● Surface tension will often cause the water level to curve up near the edges of the
graduated cylinder creating a feature called a meniscus. To accurately measure the
volume, use the lowest level the water looks to occupy.
Figure 3.5: Density Experiment: Calculated volumes (in ml) and masses (in g) of rock samples A, B, C, and D.
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4. The rock that most closely resembles the composition of continental crust is:
a. A
b. B
c. C
d. D
5. Based on your selection above, what is the density of this rock? Note: Density =
Mass/Volume. Answer unit should be in grams/milliliter. SHOW YOUR WORK.
6. The rock that most closely resembles the composition of oceanic crust is:
a. A
b. B
c. C
d. D
7. Based on your selection above, what is the density of this rock? Note: Density =
Mass/Volume. Answer unit should be in grams/milliliter. SHOW YOUR WORK.
8. Based on their densities, when oceanic and continental crust collide, the _____ crust would
sink below the ______ crust.
a. continental; oceanic
b. oceanic; continental
9. What type of boundary is represented in the question above?
a. Convergent, subduction
b. Convergent, Continental-Continental
c. Divergent
d. Transform
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Activity 3F: Plate Boundaries
Earthquakes are great indicators of plate boundaries and are associated with all three boundary
types.
1. The Wadati-Benioff zone is associated with which type of plate boundary?
a. Divergent
b. Convergent collision zone (Continent-Continent)
c. Convergent subduction zone (Continent-Ocean or Ocean-Ocean)
d. Transform
2. Download the front portion of the The Dynamic Planet map from the USGS. Which of
the following locations represent a Wadati-Benioff zone?
a. 10°S, 110°W
b. 0°, 0°
c. 15°S, 180°
d. 30°N, 75°E
3. Use GoogleEarth Pro or open the browser version of Google Earth and type
34°46’16.2″N 118°44’58.2″W into the search bar. Zoom out to an eye altitude (camera)
of 10 miles. This is Quail Lake, a dammed river that sits directly on top of the San
Andreas Fault (SAF). The SAF is a well-known transform boundary with the North
American Plate on the northern side and the Pacific Plate on the southern side. This
boundary is running East-West in this area (dashed line in Figure 3.6). Zoom out more in
Google Earth and you should be able to see it better.
4. Examine the path of the waterway that feeds into and flows out of Quail Lake. What
direction is the North American plate moving in comparison to the Pacific Plate at this
location? Draw arrows indicating the motions on Figure 3.6.
a. East
b. West
5. Given that San Francisco is located on the North American Plate and Los Angeles is
located on the Pacific Plate, are these two cities getting closer together or farther apart
over time?
a. Closer
b. Farther
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Figure 3.6: Map view of the North American and Pacific Plates.
6. Type 41°47’22.68″N, 124°15’0.51″W into the Google Earth Search bar. What type of
tectonic plates are present?
a. Ocean-Ocean
b. Ocean-Continent
c. Continent-Continent
7. What type of plate tectonic boundary is present?
a. Transform
b. Convergent, subduction zone
c. Convergent, collision zone (continent-continent)
d. Divergent
8. What features would you expect to occur at this type of boundary?
a. Volcanos, earthquakes and a trench
b. Volcanoes and a linear valley
c. Mountains and landslides
d. Earthquakes and offset rivers
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9. Type 23°26’04”N, 108°29’25”W into the Google Earth Search bar. What type of process
is going on at this location?
a. Seafloor spreading
b. Continental rifting
c. Subduction
10. What features would you expect to occur at this type of boundary?
a. Earthquakes and a trench
b. Submarine volcanic activity and earthquakes
c. Mountains and landslides
d. Earthquakes and offset rivers
11. Type 27°58’42.06″N, 86°55’11.53″E into the Google Earth Search bar. What type of
tectonic plates are present?
a. Ocean-Ocean
b. Ocean-Continent
c. Continent-Continent
12. What type of plate tectonic boundary is present?
a. Transform
b. Convergent, subduction zone
c. Convergent, collision zone
d. Divergent
13. Type 43°29’9.14″N, 128° 7’27.37″W into the Google Earth Search bar. This is known as
the Blanco Fracture Zone. What type of tectonic plates are present?
a. Ocean-Ocean
b. Ocean-Continent
c. Continent-Continent
14. What type of plate tectonic boundary does the Blanco Fracture Zone represent?
a. Transform
c. Convergent, collision zone
b. Convergent, subduction zone
d. Divergent
15. This plate boundary isn’t as simple as the previous examples, meaning another nearby
plate boundary directly influences it. Zoom out and examine the area, what other type
of boundary is nearby?
a. Divergent, continental rift
c. Convergent, collision zone
b. Convergent, subduction zone
d. Divergent, mid-ocean ridge
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