Destination: Mars - ER - NASA

The ejecta is usually more irregular thanmost of the craters.5. Have a student or group of studentscarefully outline the rims of allsharp-edged craters red.6. Show students anexample of a craterwith an uneven,eroded, brokenrim (see StudentSheet).7. Have studentscarefully outlinethe rims of alleroded cratersgreen.8. Show students anexample of a riverchannel.9. Have students color (not outline)all channels blue. They may try to showboth sides of the channel but a single lineis adequate.10. Turn off the overhead projector and askthe students what they have made. (Theyhave made a simple feature map.)11. Answer and discuss questions on StudentSheet.Questions and Answers1. Which are older - river channels or greencraters? How do you know? Greencraters are older. When a river channelmet a green crater the water brokethrough the rim, entered the crater, brokeout somewhere else, and kept going.2. Which are older - river channels or redcraters ? How do you know ? Riverchannels are older. When an impactformed a red crater on top of a riverchannel the crater covered the channel,but the crater was not eroded. The riverhad stopped flowing.3. Which features are oldest, youngest, and ofmedium age? Green craters are oldest,red craters are youngest, riverchannels are of medium age.Using the data from questions1 and 2, the greencraters were therebefore the channels,and the channelswere there beforethe red craters.4. Are big cratersolder or younger thansmall craters? Big(green) craters areolder than small (red)craters. The green craterstend to be larger while the redones are generally smaller. Thesame observation that the green craterswere there before the channels and thered craters were formed after the channelssets the larger green craters asbeing older.5. Write a simple geologic history of this part ofMars. First large meteorites hit thesurface and made big craters. Laterflowing water formed river channelswhich cut through some of the old craters.After a while the rivers stopped flowing.Even later smaller meteorites hit thesurface. Some of these formed craters ontop of the dry channels and on oldercraters.Extra credit6. What caused the difference in size betweenthe young craters and the older craters?Most of the big meteorites hit a long timeago. Later only smaller meteorites wereleft. The earlier meteorites were verylarge pieces of planetary material that10/97 NASA JSC Destination: Mars 29