Student Fact Sheet: Dirty Science

The Mission

Today, you will play the role of an extraterrestrial scientist who is investigating whether there is life on Planet Earth! You have sent a probe to Earth to collect two soil samples, and to bring them home for observation and experimentation. You will be given two samples of "soil", such as might be scooped up by your probe. The probe took these samples in two different locations: one was in a "desert" and the other was in a "forest".

Your objective is to see if you can tell by looking carefully with a microscope whether something in the soil is now alive, is dead but was once alive, or was never alive. Sometimes you will see an object that you just can't decide about. "Don't Know" is a scientifically acceptable answer. In fact, it is a better answer than a wild guess!

The Procedure

  1. Obtain a beaker of dry Earth Sample # 1 from the teacher. Gently pour (do not scoop, as scooping may damage the contents) a small, random part of Earth Sample # 1 on to two Petri dishes or other "examination dishes". Label these Petri dishes "Earth Sample # 1".
  2. Look carefully at Earth Sample # 1, first using your unaided eyes, and then using a hand lens, and finally a microscope, if one is available.
  3. Draw the objects that you see. Identify each kind of object as either "Alive", "Dead but Once Alive", "Never Alive", and "Don't Know". Look at more than one random part of each soil sample. Return each part of the sample to the beaker after it is viewed.
  4. Follow the same procedure with the second sample, dry Earth Sample # 2.
  5. Pour dechlorinated water in the beakers. Cover the "desert" soil, Earth Sample # 1, with a few centimeters of water. Just moisten the "forest" soil, Earth Sample # 2. Since this is a life-detection experiment, if there are dormant life forms in the soil, water could activate them. The drier sample requires more water.
  6. Label the watered samples with your name, so that you can retrieve your own sample the next time the class meets to examine the samples.
  7. Set these watered samples in the incubation area, under a light bulb.
  8. Use an eyedropper to take a drop of the water from on top of Earth Sample # 1 on a Petri dish. Look carefully at Earth Sample # 1, first using your unaided eyes, and then using a hand lens. Draw and classify any objects as you did before. Stir the soil sample a little and then look again.
  9. Follow the same procedure with the second sample, wet Earth Sample # 2.
Adapted from Life: Here? There? Elsewhere?, SETI Institute, Teacher Ideas Press, Englewood, CO, 1(800)237-6124 Back to Activity 9 -- Mission to Planet Earth! Life in Soil.