Student Activity
Impact Craters-4
Crater Hunters
Introduction
Impact craters are geologic structures formed when a meteorite, asteroid or
comet smashes into a planet or other solid body. All the terrestrial planets and
satellites have been bombarded throughout their history. To us the most
obvious examples of these impacts are the craters on the Moon. If the Moon is
visible, craters are visible. You can only see the very large craters or basins
with the naked eye. Lunar craters were not described until after Galileo used
one of the first telescopes to look at the Moon. Modern binoculars help to make
the craters on the Moon very obvious.
On Earth, dynamic geologic forces have erased most of the evidence of its
impact history. Weathering, erosion, deposition, volcanism, and tectonic
activity have left only a small number of impacts identifiable. Approximately
140 terrestrial impact craters have been identified. These impact craters range
from about 1 to over 200 kilometers in diameter and from recent to about two
billion years in age.
Image source: http://www.lpi.usra.edu/publications/slides/craters/slide_10.html
Part 4 has two activities. In Activity A, “Where Are the Craters on Earth,” you
will first look at other bodies in the solar system for evidence that the entire
inner solar system has a history of impacts. Then, focusing on Earth, you will
map the locations of a number of impact sites around the world. After
describing the sites based on your collected data and map, you will compare
your descriptions with aerial and satellite pictures of each crater.
In Activity B, “Crater Hunters,” you will use your documents from Activity A to
identify another possible impact crater site. Then working with your team, plan
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Student Activity
an expedition to that site to determine if it really is an impact crater or a
physical feature of the Earth’s surface formed by other actions.
Preparation
To accomplish Activity A: “Where Are the craters on Earth?” you will need the
following materials:
(1) A copy of the Procedure (below) for Activity A and Activity B
(2) The PowerPoint file Craters.ppt
(3) The Craters on Earth Data Chart
(4) Crater Hunters Map or Using ArcGIS Online tutorial with an Internetenabled computer
(5) Impact Crater Descriptions: Activity A worksheet
(6) Activity A Where Are the Craters on Earth answer sheet.
For Activity B: “Crater Hunters” you will need these materials:
(1) The Procedure
(2) Background Information for Crater Hunters
(3) materials for research and preparation of your team presentation as
recommended by your teacher.
Procedure
Activity A: “Where Are the Craters on Earth?”
Following your teacher’s instructions, accomplish these tasks in this order:
1. Gather your materials.
2. Review the images of impact craters on Mercury, Venus, Moon, and
Mars. Discuss with your classmates and teacher how these bodies are
alike and how they are different. Focus your attention on cratering.
3. Review the image of the Barringer Crater near Winslow, Arizona (“Meteor
Crater”). Propose and discuss possible answers to the question, “Where
are the craters on Earth?”
4. Plot the locations of selected impact craters on Earth. Use either ArcGIS
Online, a free online geographic information system (GIS) program for
making and printing maps, or use a blank world map available from your
teacher. If using an Internet enabled computer, follow directions in Using
ArcGIS Online tutorial.
5. As you work through the tutorial, be sure to answer Questions 1-2 on
the answer sheet.
6. Based on the age, size, name, and terrain, write a description of Spider
Crater, Manicouagan, and Clearwater Lakes impact sites using the
Impact Crater Descriptions worksheet. When finished, you should have
completed all but the right-hand column of the worksheet.
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7. Inspect the closer images of these three impact sites. Do this using both
of the following tools:
a. View and discuss slides of three impact sites in Craters.ppt
PowerPoint file.
b. Complete the Further Analysis section of the GIS tutorial.
c. Answer Questions 3-7 on the answer sheet.
8. In the right-hand column of the worksheet, try writing revised
descriptions of each of these impact craters based on the new
information you discovered upon closer inspection with newer, satellitebased imagery.
9. Answer Questions 8-11 on your answer sheet. Use well-written, complete
sentences that express complete thoughts.
Activity B: “Crater Hunters”
Following your teacher’s instructions, accomplish these tasks in this order:
1. Gather your materials including those from Impact Craters Parts 1, 2,
and 3 as well as from Part 4 Activity A.
2. Read Activity B: Background Information for Crater Hunters.
3. Following your teacher’s guidelines, discuss Background Information.
Review observations made in Activity A. If needed, review the slides in the
PowerPoint file Craters.ppt. You will be asked to brainstorm an example
crater and possible investigation of its existence.
4. Your teacher will assign a map area to investigate. Look for any feature
that might be the site of an impact.
5. Plan a geologic field investigation and laboratory tests that might be done
to verify that the site you have selected is or is not a meteorite impact
site.
6. Prepare and present a short “proposal” asking for support money to
conduct your research. You will need to explain and justify the planned
research. Consider time, travel, personnel, laboratory expenses, and data
gathering. Try to answer the question, “What would you look for at the
site to help prove that you have found the remnants of an impact?”
7. Your teacher will give you more guidelines for your presentation
including a timeline and due date.
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Craters on Earth Data
Chart
For Impact Craters-4, Activity A: “Where Are the Craters on Earth?”
NOTE: Manicouagan diameter rounded from 70-100 km to 80 km. Sikhote Alin in Russia broke up prior to impact leaving no discernible impact diameter.
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Crater Hunters Map
For Impact Craters-4, Activity A: “Where Are the Craters on Earth?”
Name ______________________________________ Date _________________ Class____________
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Student Activity
Using ArcGIS Online
Activity A: Where Are the Craters on Earth?
Preparing Your Data
The information on the Data Chart must be saved in a comma-delimited file
(.csv) before plotting your map using a geographic information system (GIS).
The file can be made using a spreadsheet program such as Microsoft Excel.
 Ensure your computer has Microsoft Excel or similar spreadsheet program installed.
 Launch the spreadsheet program.
 When a blank spreadsheet is displayed. Click in cell A1 and type Crater Name. Press
the Tab key to move to cell B1 and type Location. Similarly, type Latitude, Longitude,
Diameter (km), and Age (yr) in cells C1 through F1, respectively.
 Referring to your Craters on Earth Data Chart, type the information for Meteor Crater
in the appropriate columns in row 2. Be sure to separate the state or country name
from the crater name. Type the state or country name in the Location column. Double
check that you entered negative numbers for south latitudes and west longitudes.
 When you have finished entering all of the information from the data chart, delete all
extra worksheets, if any, so there is just the one with your data.
 Now, you will save the file:
 Click File and Save as.
 Navigate to the location designated by your teacher for saving the file.
 In the Save As dialogue, use the drop-down arrow to change Save as type to
CSV (comma delimited)(*.csv).
 Change the File name to Craters.
 Click Save.
 Close the file and exit the program.
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Plotting and Analyzing Your Map
This tutorial will guide you through the use of ArcGIS Online. The result will be
a world map with each impact crater site listed in “Craters on Earth Data
Chart” plotted and marked with a symbol indicating relative crater size. The
map can be printed but not saved.
 Ensure your computer is Internet enabled.
 Launch your browser and go to http://www.arcgis.com/home/.
 Click the Map link in the menu bar at the top of the page. You should now see a
topographic map of the United States.
 Click the Modify Map button in the upper-right of the window. Notice the Add button
appears on the left.
 Click the Add button
and select Add Layer from File. You should now see the
Add Layer from File dialogue in the center of the screen.
 Click Browse and navigate to the location of Craters.csv. Highlight the file name, click
Open. Then click Import Layer.
You should see a world map with symbols marking the location of each impact
crater on your list.
 Selecting and using pop-ups: Locate the marker for Meteor Crater in Arizona – it should
be the western-most marker in the continental United States. Click the marker symbol.
Notice a cyan (blue-green) square around the marker indicating the marker is
selected. An information pop-up also appears. Inspect the Crater Name field in the
pop-up to insure you have selected the marker for Meteor Crater. If not, click the X in
the upper-right corner of the pop-up to close it. Click anywhere on the map away from
the selected marker to deselected it (turn off the cyan square around the marker).
Repeat the process as necessary to find the correct marker.
1. How many markers appear on the map?
There should be 18. If not, you may need to backup and double check your
data entry for the comma-delimited data file.
 Zooming & Panning: Try zooming-in and out using the scroll wheel on the mouse
or the plus and minus signs on the view control bar. Return to the default view by
clicking the Home button. Try panning to other parts of the world by clicking and
holding on the map with the left mouse button and dragging the map. Finish by
zooming-in and dragging so the continental Unites States nearly fills the
screen.
 Zoom-out to the farthest extent possible. In other words, zoom-out until you cannot
zoom-out any more. The entire world should be visible in the display. Click the Home
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View button
. Europe and Africa should be in the center of the display.
2. Where is North America in the display?
It should be on the left of the screen display just above center. If not, review the
zoom and pan guidelines above and try again. Now you will modify the marker
symbol ("change style") to give it more meaning and make it easier to see.
 If the Contents panel is not visible on the left, click Details and the Content.
 Notice the Change Style panel on the left. Click the drop-down arrow to the right of the
field for  Choose an attribute to show. Select Diameter (km). For  Select a drawing style,
click the Options button.
 Click the checkbox for Classify Data. Using the drop-down and change-value arrows,
set Classify Data to Using Natural Breaks With 6 classes.
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 Use the change-value arrows to set Size to Min 15 and Max 50 px.
 Click the Legend
symbol on the right side of the Change Style panel. A duplicate
legend appears in the Change Style panel.
 Click the top symbol for >80 to 200. The Shape dialogue pops up. Scroll down to
expose the red symbols and click the round marker in the yellow row. Click OK.
 Repeat the last step until all of the size symbols have been changed according to
match this legend:
 At the bottom of the panel, click OK. Then click Done.
 In the Contents panel, notice the Craters layer is checked. What do you think will
happen when you uncheck the layer name in Contents. Try it. When finished, insure
the Craters layer name is checked.
 Use the drop-down arrow next to Craters to select Rename. In the Rename popup,
replace the existing name with Impact Craters. Click OK.
 At any time, the legend can be displayed by clicking Legend button
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Student Activity
 Zoom-out as far as possible (until the zoom-out function stops). Then click the Home
button.
Stop here. Ask your teacher to approve your map. Then follow your teacher’s
directions to obtain a printed copy of your map for each person in your team.
As you continue with your worksheets, you may use the zoom and pan tools
and pop-up windows in ArcGIS Online to help you complete the center two
columns of the Impact Crater Descriptions worksheet for Activity A.
Further Analysis
In the next step, you will view new information, provided by your teacher,
about the craters you just described. Following the guidelines below, you can
also use ArcGIS Online to see the same information in more detail. As you view
this new information, think about the descriptions you just wrote and how you
might change the descriptions based on the new information.
 Click Basemap at the top-left of the ArcGIS window. Select Imagery or Imagery with
labels. Notice the map display changes.
 Pan to Clearwater Lakes in Canada and zoom in on one marker – zoom in as close as
you can get.
3. What can you see in this image that you could not see in the other map?
4. How does the size of the marker symbol change as you zoom in?
 Zoom out until you can see enough terrain around the marker to detect impact crater
characteristics such as a crater; crater rim, floor, and wall; ejecta blanket; and ray
pattern.
An easy way to become more aware of ground distance in the map is to draw a
measurement line with a length equal to half the listed crater diameter. The
line can be drawn on the map repeatedly in several directions.
 Click the Measure button
on the button bar. The Find area, length
or location dialogue appears.
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 Click the Distance button.
Kilometers.
Use the drop-down arrow on the right to change units to
 Click once on the marker symbol on the map and release. Slowly move the cursor away
from the marker until the line length is about 11 km (that’s half of the 22 km
diameter listed for one of the Clearwater Lakes craters). Double-click to stop drawing
the line. Notice where the line ends. Repeat this step in a different direction. (Note:
The measurement lines are not permanent - each disappears when a new one is
drawn. Noting where each line ends in several directions should help you get a better
sense of actual crater size on the ground.) Click the X in the upper-right corner of the
Find area, length, or location dialogue when finished.
What do you see in the terrain now that helps define the impact crater site?
Now, try the same technique with two other craters:
 Repeat the last four steps for Manicouagan and Spider Crater impact sites. Then write
revised descriptions for each on your Impact Crater Descriptions worksheet.
ArcGIS has a built-in search tool for cities and many surface features.
 First, click the Home button to return to a global view.
 Find the Find address or place field in the upper-right of the ArcGIS window. Click in the
field once and type Reservoir Manicouagan. Then click the magnifying glass icon on the
right end of the field. The map zooms to Manicouagan Reservoir in Canada.
 It seems clear that Manicouagan Reservoir is the actual impact site, but notice the
location of the map marker for this crater. Now, click the Home button to zoom-out to
a global view.
5. Does the map marker appear to be in the correct location when viewed from a global view
scale?
6. What can you do to insure the map marker is correctly placed when the map is viewed at the
zoomed-in scale? (Hint: In your Craters on Earth Data chart, compare the listing of latitude
and longitude for Clearwater Lakes to the listing of latitude and longitude for all other impact
sites.)
7. How does this information change the way you would use the measurement tool to inspect
impact crater sites on the map?
Answer Questions 8-11 on your Where Are the Craters on Earth answer sheet.
 When finished, check with your teacher; then close your browser to exit ArcGIS
Online.
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Name_________________________________ Date____________________ Class_________________
Impact Crater Descriptions
Location and Terrain
For Impact Craters-4, Activity A: “Where Are the Craters on Earth?”
(based on info)
Description
(based on pictures)
Description
Procedure
1. Use detailed atlas or ArcGIS Online to locate the craters listed below.
2. Fill in a description of the surrounding terrain; especially consider the geology of the area.
3. Considering all the information on the Data Chart, write a description of what you think the craters look like.
4. View the pictures and detailed views in ArcGIS Online and write your second descriptions based on the pictures. Then, compare the descriptions.
Crater
Clearwater Lakes
Size
22 km diam. and
32 km diam.
Age
240 million yr.
Manicouagan
Size
70-100 km diam.
Age
212 million yr.
Spider crater
Size
13 km diam.
Age
< 600 million yr.
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Name_________________________________ Date____________________ Class_________________
Where Are the Craters on Earth?
Activity A Answer Sheet
Answer Questions 1-4 as you work through the ArcGIS Online tutorial:
1.
How many markers appear on the map?
2.
Where is North America in the screen display?
3.
What can you see in this image that you could not see in the other map?
4.
How does the size of the marker change as you zoom in?
5.
Does the map marker appear to be in the correct location when viewed from a
global view scale?
6.
What can you do to insure the map marker is correctly placed when the map is
viewed at the zoomed-in scale? (Hint: In your Craters on Earth Data chart,
compare the listing of latitude and longitude for Clearwater Lakes to the listing of
latitude and longitude for all other impact sites.)
7.
How does this information change the way you would use the measurement tool to
inspect impact crater sites on the map?
Answer Questions 8-11 after you complete the descriptions on the Impact Crater
Descriptions worksheet for Activity A.
8.
Where are the craters on Earth?
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Name ________________________________________ Date _________________ Class____________
9.
What happened to the craters on Earth?
10. What are some differences between Moon craters and Earth craters?
11. Compare several Earth craters. How are they alike and different?
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Impact Craters-4
Activity B: Background Information for Crater Hunters
Scientists perform extensive field and laboratory research before they are able
to verify that a geologic feature is an meteorite impact site. Ideally the scientists are
looking for round structures, however geologic forces may have distorted the crater
shape through faulting or other movement associated with plate tectonics. Ice, water,
and wind, weathering and erosion processes have caused great changes in craters.
Some craters have been filled with water, or completely covered by soil or water, and
have no surface evidence. They may initially be identified by remote testing of
materials below the Earth’s surface (geophysical studies).
Some of the clues that help scientists identify large impact sites are found in
the physical condition of the structure. In addition to the crater’s round shape, they
look for layers of rock that have been turned over at the edge of the crater. A large
uplift or mountain at the center is also common in impact craters. Highly fractured
rocks are usually found at impact sites but they could be interpreted as being
associated with other non-impact geologic processes. However, scientists find shatter
cones, which are highly shocked rocks with distinct structures, only at areas stressed
by huge impacts. Investigations usually identify large amounts of excavated material
deposited around and in the craters. This material is called ejecta and may form thick
layers of breccia, a mixed broken rock material. To verify the location and origin of
these deposits requires extensive research, including drilling. Sometimes a large
volume of impact-melted rock is found in and around the craters. Some melted rock is
frequently thrown far from the impact. These small glassy masses, which were
aerodynamically shaped when they were molten, are called tektites. Very small ones
are micro tektites. They are good indicators of large impacts.
Another way to get important information about an impact is from chemistry.
The impact-melted rock sometimes contains melted meteorites. By careful laboratory
research, scientists can detect very small amounts of rare elements that are more
abundant in meteorites. These chemical signatures are very important in meteorite
research. To find a meteorite sample would be the best discovery! Unfortunately this
does not happen frequently. Meteorites may completely vaporize during the impact
process, or they may be removed by erosion.
Early geologists misinterpreted some impact craters. Scientists reported Meteor
Crater in Arizona as a volcanic crater. The Chicxulub site on the Yucatan peninsula
was also wrongly reported. Early oil explorers misinterpreted extensive deposits
around the Chicxulub area. Scientists now know that the material is ejecta from a
huge impact and not of volcanic origin.
Considering the geologically active crust that erases craters, and all the
research necessary to verify the origin of impact craters, it is not surprising that only
around 140 have been identified so far. But it is likely that more will be found.
Adapted from “Lesson 7 – Crater Hunters,” Exploring Meteorite Mysteries, NASA Publication NASA EG-1997-08-104-HQ
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