Crater counting: worksheet

Draw a boundary between the two main geological units, roughly halfway up the image: smooth terrain in the north and undulating terrain in the south. Their ages differ, so treat them separately. Count craters in both areas in each size range and enter approximate counts in the table. Consult the crater production table: how many craters in each size range form on a surface of a given age? Estimate the ages of the two units by finding the table values that best match your counts. Erosion may have removed small craters.

Plot the two sets of counts on the vertical lines using X and dot symbols. Join them with dotted or continuous red lines. The terrain with the densest craters, especially large ones, is the oldest.