Geologists use maps to illustrate the history of a place. Geologic maps show what is there, and which features were formed earlier or later than others (not an exact time but a relative time sequence). On earth, we make these maps using photographs from airplanes and evidence we find on the ground. To make maps of other planets, we must use photographs taken from spacecraft.

Students will make a simple map and interpret the geologic history of a part of the Mars' surface.

Materials:

Transparency made from a Mars surface photograph
Click here to get the MARSMAP!!MARSMAP.JPG (110K)  MARSMAP.GIF (270K)

Overhead projector
Mars Activity packet consisting of Mars Image, procedures, and questions.masking tape
Colored markers or pencils(3 colors-red, green, and blue are used in the discussion below)

Procedure:

1. Issue each student an activity packet consisting of a copy of the Mars Image and directions and questions

2. Project the Mars image fior students to observe during the activity.

3. Tell students that this is a satellite image of an area on Mars that shows impact craters and river channels.  Noone has ever been here, but we can figure out things about this part of Mars by mapping and by thinking critically. The image is of an area on Mars around 18 degrees North Latitude and 55 degrees West Longitude, at the northern edge of Chryse Planitia and is oriented toward the Martian North Pole.

4. Show students an example of a crater with a continuous, sharp-edged, unbroken rim. Note that they should draw the rim and not the fairly flat interior. If time and skill allow, students may also note and draw the ejecta for the fresh sharp rimmed craters. The ejecta is the material that is blasted out of the crater and falls outside the rim of the crater. The ejecta is usually more irregular than most of the craters.

5. Have a student or goup of students color all sharp-edged craters red.

6. Show students an example of a crater with an uneven, eroded, broken rim.

7. Have students color all eroded craters green.

8. Show students an example of a river chanel.

9. Have students color all river channels blue (They may try to show both sides of the channel, but a single line is adequate).

10. Turn off the overhead projector and ask the students what they have made.

They have made a simple feature map!

Question 1. Which are older, river channels or eroded  craters? How do you know?

Answer: Eroded  craters are older. When a river met a crater, the water broke through the rim , entered the crater, broke out somewhere else, and kept going.

Question 2. Which are older, river channels or sharp rimmed craters? How do you know?

Answer: River channels are older. When an impact formed a sharp rimmedcrater on top of a river channel, the crater covered the channel, but the crater was not eroded. The river had stopped flowing.

Question 3. Which features are the oldest, youngest, and of medium age? What is your proof?

Answer: Eroded  craters are the oldest, sharp rimmed craters are youngest, and the river channels  are medium age. Using the data from questions 1 and 2, the eroded craters were there before the river channels, and the channels were there before the sharp rimmed craters.

Question 4. Are big craters older or younger than small craters? What is your proof?

Answer: The big  craters are older than small craters. The green craters tend to be larger while the red craters are generally smaller. The same observation that the green craters were there before the river channels and the red craters were created after the river channels, sets the larger craters as being older.

Question 5. Write a simple geologic history of this part of Mars.

Answer: First, large meteorites hit the surface and made big craters. Later, flowing water formed river channels which cut through some of the old craters. After a while, the rivers stopped flowing. Even later, smaller meteorites hit the surface. Some of these formed craters on top of the dry river channels.

Question: Why are the old craters larger than the young craters?

Answer: Most of the big meteorites hit a long time ago. Later, only smaller meteorites were left. The earlier meteorites were very large pieces of planetary material that were still being pulled together through the process of solar system accretion. As time passed, the impacts were caused by the smaller pieces of material left over from the accretion process.

Question: Which way does the land slope? Explain your answer.

Answer: The land slopes to the west southwest. River channels combine as you go downhill. Looking at a map of the Mississippi River drainage basin or some other terrstrial river basin may be used as a comparison.