Name:
Skill Sheet 28-A
Relative Dating
Relative dating is a method used to determine the general age of a rock, rock formation, or
fossil. When you use relative dating, you are not trying to determine the exact age of
something. Instead, you use clues to sequence events that occurred first, then second, and so
on. A number of concepts are used to identify the clues that indicate the order of events that
made a rock formation.
1. Relative dating concepts
The following situations illustrate relative dating concepts. Match each situation to the terms
listed below the graphic. Write the letter of each situation in the blank next to each term.
1.
2.
3.
4.
5.
6.
Superposition _____
Original horizontality _____
Lateral continuity _____
Cross-cutting relationships _____
Inclusions _____
Faunal succession _____
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2. Determining the order of events in a geologic cross-section
1. Use arrows to indicate the direction in which the following rock layers were compressed to
make a metamorphic rock.
2. For the graphic at right, indicate the order in which the rock layers
formed. Some layers formed at the same time. What relative dating
concepts did you use to determine the order of the rock layers?
3. Look carefully at the graphic at right. Why is layer B smaller than
layer A? Which direction did the fault shift? How do you know?
4. Two faults are shown in this geologic cross-section at right. Place
the rock layers and the two faults (A and B) in the order in which
they happened.
5. This geologic cross section shows some rock layers that have
undergone metamorphism. When did the metamorphic event happen
relative to the other features in the graphic?
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6. Did the intrusion in this cross-section happen before or after layer A
was formed? Justify your answer.
7. Look at the two intrusions in this picture. Explain the appearances of
the top of each. Why is one top flattened while the top of the other
intrusion is rounded? Place the rock layers and intrusions in the order
in which they happened.
8. Examine this geologic cross-section.
a Why might the rock layers in this cross-section be wavy? Come up
with an explanation.
b There are two fossils located at positions A and B. Which fossil is
older? Justify your answer.
3
Name:
Skill Sheet 28-B
Using a Bathymetric Map
Imagine that all the water in the oceans disappeared. If this happened, you would be able to
see what the bottom of the ocean looks like. Fortunately, we don’t have to drain water from
the ocean to get a picture of the ocean floor. Instead, scientists use echo sounding and other
techniques to “see” the ocean floor. The result is a bathymetric map. This skill sheet will
provide you with the opportunity to practice reading a bathymetric map.
1. Main features on a bathymetric map
1. Main features on a bathymetric map are mid-ocean ridges, rises, deep ocean trenches,
plateaus, and fracture zones. Find one example of each of these on a bathymetric map.
a. Mid-ocean ridge:____________________
b. Rise: ____________________
c. Deep ocean trench: ____________________
d. Plateau: ____________________
e. Fracture zones: ____________________
2. All the ridges you see on the bathymetric map behave in the same way even though they may
not be in the middle of an ocean. What happens at mid-ocean ridges?
3. Find the Rio Grande Rise on the bathymetric map. Then, find the East Pacific Rise.
a. Which of these features is an example of a mid-ocean ridge?
b. Find another example of a rise that is a mid-ocean ridge. Justify your answer.
c. Find another example of a rise that is not a mid-ocean ridge. Justify your answer.
4. There are a number of deep ocean trenches on the western side of the North Pacific Ocean.
What process is going on at these trenches?
5. What plate tectonic process probably caused the fracture zones in the North Pacific Ocean?
Justify your answer.
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2. How is the East Pacific Rise different from the Mid-Atlantic Ridge?
1. Look carefully at the Mid-Atlantic Ridge. Describe what this ridge looks like. Be detailed in
your description.
2. Now, look carefully at the East Pacific Rise. Describe what this ridge looks like. Be detailed in
your description.
3. Which of these features has a noticeable dark line running along the middle of the feature?
Look at the legend at the bottom of the map. What does this dark line indicate?
4. Based on your observations of these two features, draw a cross-section of each in the boxes
below.
Mid-Atlantic Ridge cross-section
East Pacific Rise cross-section
5. One of these mid-ocean ridges has a very fast spreading rate. The other has a very slow
spreading rate. Which one is which? Justify your answer based on your answer to questions 3
and 4.
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Name:
Skill Sheet 28-C
Finding an Earthquake Epicenter
The location of an earthquake’s epicenter can be determined if you have data from at least
three seismographic stations. To find the epicenter, you need to know the arrival times and
speeds of the P- and S-waves. The only other items you need are a calculator and a compass.
1. The equation for finding the epicenter
To calculate the distance to the epicenter for each station, you will use the equation:
Distance = Rate × Time
Table 1 lists the variables that are used in the equation for finding the distance to the epicenter.
This table also tells you which values are given to you and which values you need to calculate.
Table 1: Variables for the equation to calculate the distance to the epicenter
Variable
What it means
Given
Need to calculate
dp
distance traveled by P-waves
rp = 5 km/sec
rp
speed of P-waves
rs = 3 km/sec
tp
travel time of P-waves
ds
distance traveled by S-waves
rs
speed of S-waves
ts
travel time of S-waves
ts = travel time of Pwaves plus the time
between the P- and Swaves
dp, tp, and ds
For each of the practice problems, assume that the
speed of the P-waves will be 5 km/sec and the speed of
the S-waves will be 3 km/sec. Also, because the P- and
S-waves come from the same location, we can assume
the distance travelled by both waves is the same.
distance traveled by P-waves = distance traveled by S-waves
dp = ds
rp × tp = rs × ts
Since the travel time for the S-waves is longer, we can say that,
travel time of S-waves = ( travel time of P-waves ) + ( extra time )
t s = t p + ( extra time )
r p × t p = r s × ( t p + extra time )
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2. Practice problems
For each of the practice problems, assume that the speed of the P-waves is 5 kilometers per
second, and the speed of the S-waves is 3 kilometers per second. The first problem is done for you.
Show your work for all problems.
1. S-waves arrive to seismographic station A 85 seconds after the P-waves arrive. What is the
travel time for the P-waves?
3 km
5
km-----------× t p = ------------- × ( t p + 85 sec )
sec
sec
km-⎞
3 km
⎛5
-----------= ⎛ -------------⎞ t p + 255 km
⎝ sec ⎠ t p
⎝ sec ⎠
km-⎞
⎛2
-----------t = 255 km
⎝ sec ⎠ p
t p = 128 sec
2. S-waves arrive to another seismographic station B 80 seconds after the P-waves. What is the
travel time for the P-waves to this station?
3. A third seismographic station C records that the S-waves arrive 120 seconds after the Pwaves. What is the travel time for the P-waves to this station?
4. From the calculations in questions 1, 2, and 3, you know the travel times for P-waves to three
seismographic stations (A, B, and C). Now, calculate the distance from the epicenter to each of
the stations using the speed and travel time of the P-waves. Use the equation: distance =
speed × time.
5. Challenge question: You know that the travel time for P-waves to a seismographic station is
200 seconds.
a. What is the difference between the arrival times of the P- and S-waves?
b. What is the travel time for the S-waves to this station?
2
3. Practice problems: Locating the epicenter
Table 2 includes data for three seismographic stations. Using this information, to perform the
calculations that will help you fill in the rest of the table.
Table 2: Calculating the distance to the epicenter
Variables
Station 1
Station 2
Station 3
Speed of P-waves
rp
5 km/sec
5 km/sec
5 km/sec
Speed of S-waves
rs
3 km/sec
3 km/sec
3 km/sec
Time between the arrival of
P- and S-waves
rs - rp
70 seconds
115 seconds
92 seconds
Total travel time of P-waves
tp
Total travel time of S-waves
ts
Distance to epicenter
dp, ds
Once you have calculated distance to the epicenter for three stations, you can use a map to locate
the epicenter. The steps are as follows:
Step 1: Draw a circle around each seismographic station. The radius of the circle should be
proportional to the distance to the epicenter.
Step 2: The place where all three circles intersect is the location of the epicenter.
1. In Table 2, you calculate the distance to the epicenter for three seismographic stations.
Convert each of these distances in kilometers to centimeters using the scale, 200 kilometers =
1 centimeter. Use proportions to perform the calculation:
1 cm
x
-------------------- = ---------------------------------------------------------------------------200 km
distance to epicenter in km
3
2. Now, use the values you calculated in question (1), the graphic below, and a geometric
compass to make circles around each station. Remember that the radius of each circle is
proportional to the distance to the epicenter.
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Name:
Skill Sheet 29-A
Interpreting Geologic Hazard Maps
Plate tectonics and the weather are often the cause of geologic hazards such as earthquakes,
volcanic eruptions, and flooding. Geologic hazard events are important to understand because
they often cause loss of life and property damage. Geologic hazard maps are used to help
prevent loss of life and property damage should these events occur. On this skill sheet, you
will practice interpreting geologic hazard maps.
1. Earthquakes
This map illustrates the areas that were affected
by two major earthquakes -- one in 1895 and one
in 1994. Study this map and then answer the
questions. Graphic courtesy of the USGS.
a. The darker shade of gray represents
significant damage to buildings in the area.
The lighter shade indicates that shaking was
felt but very little damage occurred. Why do
you think the affected area for the 1895
quake is so much larger than the area
affected by the 1994 earthquake even though
the two quakes had similar magnitude?
b. Why is the area affected by each earthquake circular or nearly circular? Where is the epicenter
of each quake located?
c. Use the scale at the bottom of the map to determine the approximate the radius of the area
affected by each quake.
d. In which location might earthquakes be more frequent? Justify your answer.
e. In which location might earthquakes be more damaging? Justify your answer.
1
f. The Richter scale was developed in 1935. How do you think scientists figured out the Richter
scale value for the 1895 quake long after the earthquakes occurred?
2. Tsunamis
This map shows the evacuation route for a community in the event of a tsunami. Study the map
and then answer the questions. The white area of the map represents water.
a. What do you think the term “evacuation zone” means?
b. In the event of a tsunami, would the schools be a useful building for people to gather? Explain
your answer.
c. In the event of a tsunami, would it be safe to travel on highway 1? Explain your answer.
2
d. Evaluate the effectiveness of this map. If you lived in this region, would you feel like you knew
all that you needed to know to keep safe if a tsunami occurred? Explain your answer.
e. If you lived in this community, how would you help citizens know that they were in an
evacuation zone or a safe zone?
3. Flooding
Here is a map of the amount of stream flow for the
month of October. Study the map and then answer the
questions.
a. How might this map look in January? Justify your
answer.
b. How might this map look in July? Justify your
answer.
c. Where on this map might flooding be a problem? Why?
d. What geographical feature is associated with the high stream flow region in Mississippi and
Alabama?
3
4. Volcanoes
In this exercise, you will turn the map at right into a geologic hazard map by following a series of
steps. Features on the map include Mount Rainier and neighboring cities and rivers in a region of
Washington State.
1. Step 1: It is likely that earthquakes would occur
prior to an eruption of Mount Rainier. Earthquakes
are one of the geologic hazards for this area. Draw
a symbol on the map that indicates that this region
experiences earthquakes.
2. Step 2: In the event that Mount Rainier erupted,
ash and pyroclastic material would possibly spread
out from the volcano. The most threatened area
would be within 50 km of Mount Rainier. The town
of Puyallup is about 50 km from Mount Rainier.
Draw a a circle around Mount Rainier that
illustrates the threat of ash and pyroclastic flow.
Shade in this circle.
3. Step 3: Mudflows would probably follow an eruption. Based on the past (ancient) history of
eruptions of Mount Rainier, scientists predict that these mudflows would travel down the
White River and Puyallup River after an eruption. Indicate on the map that these mudflows
may occur and affect regions near these rivers.
4. Step 4: Now that you have completed steps 1 - 3, the graphic is a geologic hazard map. To
make the map easier to interpret, add a legend that explains the symbols or shading you
added.
5. Step 5: The chances that these events may occur range from once in 1,000 years to once in
100,000 years. In terms of percentage, there is a 0.1% to 0.001% chance that Mount Rainier
could erupt this year. Therefore, the likelihood of an eruption is very low but possible. If you
were a public official, how would you help citizens be prepared for but not scared of an
eruption? Write your answer as a short paragraph below.
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5. Sinkholes and Karst Topography
Karst topography happens when underground limestone beds are eroded by acidic water or when
water in an aquifer becomes depleted. The loss of limestone or water results in underground gaps,
tunnels, and caves. The surface of the ground in these regions may become bumpy. Sinkholes
occur when the ground above the gaps and tunnels collapses. In regions where there is a lot of
underground limestone, karst topography and sinkholes are common.
Imagine you are a member of the school board for your town, a place known for its karst
topography. At the next meeting, the board needs to select the site where it will build a new high
school. There are four possible locations where the school board could build the school.
To prepare for the meeting, you have a couple of maps to review. One map indicates the sites of
karst topography. The other map indicates the type of sediment and rock that is in the area
(A - D). Each map shows a general road map of the town and the four possible locations for the
school. It is very important that the school be built in a location that allows for traffic flow.
Study each of these maps and select the best location for the school. Write a short paragraph
justifying your selection.
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Name:
Skill Sheet 29-B
Mohs Hardness Scale
Mohs hardness scale was developed in 1812 by Friedrick Mohs (an Austrian mineral expert) as
a method to identify minerals. This scale uses 10 common minerals to represent variations in
hardness. You can identify a mineral’s place on the hardness scale by whether it can scratch
another mineral. For example, gypsum (hardness = 2) scratches talc (hardness = 1). The
hardest mineral, a diamond, can scratch all other minerals. Pure minerals of the same hardness
scratch each other. In this skill sheet, you will practice using Mohs Hardness Scale and work
with the minerals in your Rocks and Minerals Set.
1. Collecting the minerals of Mohs Hardness Scale
1. From your Rocks and Minerals Set, collect the minerals listed in Table 1. The only mineral
you will not find is a diamond. Why?
2. The piece of porcelain in the set is used to determine the streak color of minerals. Scratch each
mineral on the porcelain and record the streak color in the third column of Table 1.
3. In the fourth column, describe what each mineral looks like. Describe its color, texture, and
anything else that would help you distinguish this mineral. Use the small magnifying glass in
the kit to help you.
Table 1: Mohs Hardness Scale
Hardness
Color of Streak on
Streak plate
Mineral
Talc
1
Gypsum
2
Calcite
3
Fluorite
4
Apatite
5
Orthoclase (Feldspar)
6
Quartz
7
Topaz
8
Corundum
9
Diamond
10
N/A
Description
clear, sparkly
1
2. Applying your knowledge
a. Prove to yourself that the placement of the minerals on the Mohs Hardness Scale is correct.
How would you do this? Write your procedure as a short paragraph and then perform the
procedure.
b. Is the Mohs Hardness Scale value for a mineral a quantitative or a qualitative number?
Justify your answer to this question.
c. List two pros and two cons for using the Mohs hardness scale to identify minerals.
d. Is the Mohs Hardness Scale useful for identifying rocks? Why or why not.
e. Some varieties of the mineral corundum are gemstones. Rubies and sapphires are two
examples. Imagine that you have heard a report that there is a newly discovered mine that is
rich in corundum. You have been hired to verify the reports. For your first field trip, design
two tests you will use to determine if the mineral in the mine is in fact corundum.
2
3. What are the hardness values for other objects?
When geologists are in the field, they do not have a whole set of mineral samples to represent each
hardness value on the Mohs Hardness Scale. Instead, they often use things like a pocket knife or
their fingernail to identify the hardness of mineral samples.
Use the clues (a - g) to help you identify the hardness values for the objects listed in Table 2. First,
read the following instructions for how to fill in the table.
Instructions for filling in Table 2: In the top row are items that you could use to identify the
hardness of a mineral. Read the clues to identify the hardness of each. The information in Table 1
will be helpful to you as well. Place a circle (O) in the table cell where the object and its hardness
match. Where hardness and the object do not match up, place an X. The first two clues are done
for you to illustrate how to fill in the table.
Clues:
a.
b.
c.
d.
e.
A diamond is considered to be the hardest mineral.
Pyrite is harder than calcite.
The hardness of a fingernail is 2.5. Ice does not leave scratches on a fingernail.
Calcite and copper have similar hardness.
A pocketknife is a good tool to take on geology field trips. A pocket knife is helpful in that it can
scratch half of the minerals on the Mohs Hardness Scale.
f. Pure apatite and fluorite can be scratched by iron. Iron can be scratched by quartz.
g. A pocket knife can scratch fool’s gold.
Copper
wire
Table 2: Mohs Hardness Scale
Pocket
Pyrite
Diamond
knife
1.5
X
X
3
X
X
4-5
X
5.5
X
6 - 6.5
X
10
X
X
X
O
3
Iron nail
Ice
X
X