(This observing exercise is geared for middle and high school students.)


The Earth's surface is extremely dynamic. Plate tectonics and a variety of erosion processes have removed ancient features. Scientists assume that the Moon and Earth were created at the same time and by rather identical processes. By studying the Moon's surface, which still retains its scars from 3 to 4 billion years ago, we can also learn about the earlier history of the Earth.


An informative technique is to count craters of various sizes in different regions on the surface. The assumption is that all of the regions should have received the same number of impacts. If a region has fewer, then some other event or multiple events is believed to have removed the evidence.


1. Count the number of craters in a highlands region and try to bin these into small, medium, or large diameter, if possible. Record your number of each group in the table below. Now count the number of craters in a maria region, and use the same crater-size bins. (Try to use equal surface areas for the highlands and maria crater counting.) Notice whether there are more craters toward the center of the maria or near the edges. Record the maria crater counts in the table.


Number of Craters       Highlands          Maria       

    Small-sized                     |                              |                            |

    Medium-sized                  |                              |                            |

    Large-sized                     |                              |                            |


2. Which region has more craters? What would cause one region to have fewer craters? Using your answer, can you make a hypothesis as to which region is older? Why?


3. What have you learned from looking at the surface of the Moon that may also be applicable to studying the surfaces of Mercury and Mars?



James Sowell, 2013