Step 1 . Use
students' interest in the highly dramatic, explosive to introduce
the activity.
Show students an aerial photograph of Barringer Meteor Crater (also
known as "Meteor Crater", and located in Arizona). Tell
them this landform is about 1300 meters (0.8 mile) in diameter and
174 meters (570 ft) deep. Ask them, what do you think could have made
a hole this big in the land? Discuss as a class.
Show an artist's rendering of an impact event. Two are provided.
1.
"One Minute After the End of the Cretaceous" by William
K. Hartmann
Please be aware that
anyone reproducing this painting for uses other than this classroom
activity, "Finding Impact Craters with Landsat" must contact
William K. Hartmann for his permission, at: <hartmann@psi.edu>
or by using information at this URL:
http://www.lpi.usra.edu/publications/books/CB-954/CB-954.intro.html
2. Impact Painting by Don Davis
Tell students that many objects much smaller than a planet orbit
the Sun, and sometimes the Earth's path crosses theirs. When that
happens, there is an impact event of enormous force, with profound
effects on rocks and soil, atmosphere, water, and living things.
Ask students to imagine hitting a dust particle or a fleck of paint
in the air with their finger. They will understand that such a collision
would not leave any lasting mark. Tell them that NASA engineers
working on the Space Shuttle have found that even tiny flakes of
paint floating in space (from earlier missions) can make craters
one centimeter in diameter in Space Shuttle windows when they hit
them, because of the speed of impact. Emphasize that there is a
lot of energy in an object traveling fast. It has been calculated
that the energy required to produce the Barringer crater was equivalent
to the explosion of 15 million tonnes of TNT.
Have a discussion about what students may already know about impact
events. Ask students if any of them have visited Barringer Meteor
Crater. Students who have done so can describe their experience.
Do the following either in the classroom or as homework the night
before you wish to conduct the bulk of the lesson:
Distribute the Student Worksheet for Step 1, "When an Extraterrestrial
Object Hits the Earth".
On the worksheet, students read a short description of what happens
during an impact event. Based on that reading and on their existing
knowledge, they describe the effects such an event might have on
the land, air, and living things, and evidence of these effects
that might remain for thousands or millions of years.
In the classroom:
Step 2. Distribute Student Reading for Step 2: Known
Effects of Impact Events, and have students read quietly alone or
aloud together.
Step 3. Show either of the following, both of which
are provided with this activity:
(a) the movie,
"Iturralde Movie" ~or~
(b) the series of three still images
from the Iturralde movie, which is provided with this activity.
Explain to students that the movie is comprised of Landsat images
of a location in Bolivia, as the movie progresses the data are displayed
in various way so that the impact crater becomes more visible to
the viewer. The movie and the series of still images taken from
it show very clearly how satellite technology helps us see landforms
hidden in the Earth's surface that we cannot see with our eyes alone.
Step 4. Organize
students in small groups (of three to five students). Distribute the
following:
(1) One set of seven satellite images to each group
(2) One copy for each student of the Student Worksheet Sheet for
Step 4: Describing Satellite Images of Possible Impact Craters
Given what students know about the evidence left by impacts, ask
student groups to determine whether or not the landforms in all
seven of the images appear to be impact craters.
Guidance questions are provided on the Student Worksheet.
Monitor the student groups as they discuss their analyses
of the satellite images.
1. Make sure students understand that they should come to agreement
as a group about their satellite images based on their analysis
of the evidence in the images.
2. The Student Worksheet provides instructions about sharing their
thoughts about the evidence before coming to agreement as a group.
As groups discuss their analyses of the images, make sure they
are discussing the evidence constructively with each other.
3. If students do not follow these instructions in the worksheet,
direct them to choose one or two of the satellite images they
find most interesting to interpret for the class, and to designate
a spokesperson for the group.
Step 5. Have each spokesperson interpret the group's
images. Make sure that all of the images in the set provided are covered
in the class discussion.
Whether or not students believe each image shows an impact crater,
their spokesperson must explain their group's thinking clearly and
convincingly.
For positive identifications of the landforms as needed, use the
Teacher Reference for Step 5: The
Landforms Identified.
Either in the classroom or as homework:
Step 6. Distribute Student Worksheet for Step 6:
Questions You Would Ask on a Field Expedition to a Possible Impact
Crater
Ask students to write a set of questions for researchers going on
a field expedition to an unidentified landform. The questions should
serve well as guidance to determine whether or not the landform could
be positively identified as an impact crater.
Download
this lesson plan in PDF format.
Thursday, August 14, 2003