They are trying to detect life forms on earth and determine what these life forms do. The objective is to build awareness of the effects humans have on their environment. It may help to take a walk in your local area and use the table to record human signs. You could use local maps or aerial photographs to help the students brainstorm through the human 'signs' list. Each student outlines their footprint onto a thick piece of clear plastic or Mylar.
Students take their footprint and place it onto a grassy patch.
They should then try to count the number of plants their footprint covers. Repeat the counting excercise near paths at some other interesting location, e.g. slopes. Ask the children to explain any differences in the number of plants in different locations. If you have access to a sand pit or muddy area, rake the area smooth. Then ask one student to walk in a straight line across the park.