Universe Cycle - Earth (5)
Post Lab 

   
OBJECTIVES:
  • Comparing the landforms of Mars and Earth.
  • Exploring the real meaning of photos and maps.
VOCABULARY:
  • channel
  • glacier
  • Martian
  • surface
  • valley
MATERIALS:

Students look at photographs of the surface of Mars.


A full view of Mars. Note the abundant meteorite impact craters
 

BACKGROUND:



Canyons and valleys - evidence of erosion by landslides and  (?) water

Mars, more than any other planet, has characteristics that would seem to make it an Earth-like world. Its period of rotation and the inclination of its axis are similar to those of the Earth. Mars is similar in composition to the Earth, but probably has less iron and more lightweight elements. Finally, only Earth and Mars, among the inner planets, have satellites. However, the surfaces of Earth and Mars are very different. The Earth’s surface is continuously modified. Plate tectonics changes the locations of such features as continents, ocean basins, mountain ranges, and volcanoes. The abundance of water on the Earth’s surface enhances the weathering and erosion of material on the surface. High areas are destroyed and low areas are filled in. Finally, the activity of life enhances weathering and erosion of the surface, and has drastically altered the composition of the Earth’s atmosphere and oceans.


Olympus Mons Volcano - 
25 Kilometers high!

In contrast to the Earth, the surface of Mars is very old, and changes very slowly. Mars is slightly more than one quarter of the volume of Earth. This means that the interior of the planet has largely cooled off. Mars thus lacks major tectonic activity, although Marsquakes have been detected. The abundance of large volcanoes and wide rift valleys on its surface testify to past events, but these features are all more than several hundred million years. Mars also lacks surface water. Again, there is evidence that water may have flowed on Mars early in its history (billions of years ago) but now the surface of the planet is very dry. None of the Earth’s usual water related surface processes including streams, glaciers, and ocean, are active on Mars. However, spacecraft have photographed abundant sand dunes on the Martian surface, as well as dust storms in the atmosphere. These indicate that wind processes are still active on Mars, just like on Earth. There is currently no evidence for life on Mars.


A view of the Martian surface from the viking 1 lander. Note sand dunes.

The surface of Mars is marked by abundant impact craters. These formed when asteroids struck the planet. The Earth is also hit by extraterrestrial objects, but here craters are quickly destroyed by erosion and surface processes. This difference is another indication that the surface of Mars is old.

However, there is a feature on Mars that is somewhat similar to Earth, especially the canals that look like great rivers. Some scientists feel that these are evidence that water was once present on the surface. These channels have a curious history. After they were observed by Pietro Secchi in 1876, Giovanni Schiaparelli made a map of them in 1877. The map used the Italian word canali which means channel. English speaking countries thought they meant canal, which is a human-made structure and stories began of Martians. These stories were widespread up to the middle 20th century. In our language, the term Martians is commonly used to describe inhabitants from other planets. These channels are probably of water origin, and were present when the atmosphere supported water.


Another viking lander view of the surface of Mars

PROCEDURE:


Martian windblown soil, with the Pathfinder rover for scale. 

  1. Have students look at a 3 dimensional  model of the Earth (hydrographic globe) and visualize looking at the surface from different angles. The objective is to make students realize that it is difficult to make observations of a planet we do not fully understand. Another important point is to for students to compare the differences between the landscapes of Earth and Mars. Students should realize that the Earth is unique because is has so many agents of erosion. This creates a land full of water that supports living organisms.
      
  2. Instruct students to look at the plastic landform model of the surface of the Earth. Imagine your eyes as a camera. Look at the landscape in the five positions drawn in the diagram. Ask students the questions below. Read the questions first, so that you have an idea of what to observe.
     
    1. What would be the best position to use to take a picture the model that would show all of its features?
    2. Which position shows the true width of objects on the model?
    3. Which position most distorts the shapes of objects?
    4. Which position best shows the height of mountains?

    Answers:
    A. from position 3; B. position 3; C. position 2 and 4; D. position 1 and 5;
     

  3. As students look at pictures of Mars, which can be found on the Internet, or use the ones in the background information, ask them if they can visualize what the surface of Mars looks like. On each photo you look at, ask students about which angle the picture was taken. You may want to use the Internet for recent photos of Mars to enhance this activity.

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