Activity 9 -- Mission to Planet Earth! Life in Soil

Can You Recognize Life Up Close?

Overview

In Part One of this Activity, students examine two "soils"; an artificial mixture that appears lifeless, and a natural Earth soil, which appears full of life. Both represent samples that might be taken by the extraterrestrial probe. The students describe what they see and then cover their mixtures with water. In Part Two, students discover that the apparently lifeless soil is now filled with brine shrimp which have hatched from dormant eggs in the soil. Students realize that simply looking at something may not be the best way to detect life. Putting water on a soil sample is one way of "activating" any dormant life.

PART ONE

What You Need

For a Class of 30:

• 3 Vials (6 grams) Brine Shrimp Eggs
• 1 cup clean or sterile fine-grained sand
• 1/2 Tbs. salt
• 2 cups organic topsoil from an unsprayed garden
• 2 50 ml beakers (demonstration)
• "Incubation Center", an area kept warm (light bulbs)
• Chemicals to dechlorinate water
• Dechlorinated water in a large container
• Cups for students to transport water
• Stick-on labels or grease pencils
• Optional: 4 dozen very small, colored glass beads

For Each Team of Students:

• 2 50 ml beakers
• 2 Hand lenses
• 2 Petri dishes or equivalent "Examination dishes"
• 1 Low-power microscope or stereo microscope (if microscopes are not available, use hand lenses)
• 2 Dissection needles or probes

For Each Student:

• Student Fact Sheet: Dirty Science
• Student Worksheet: Observing Dry Soil Samples

Getting Ready

2. Make Earth Probe Samples: Prepare "Earth Probe Sample # 1" beakers and "Earth Probe Sample # 2" beakers for each team as follows. Label each beaker "Earth Sample # 1" or "Earth Sample # 2" with a stick-on label or grease pencil. For "Earth Sample # 1", gently mix the following ingredients in a clean container.

• Fine sand
• Salt (preferably coarse, "rock salt"
• Brine shrimp eggs
• Optional: small, colored glass beads

3. Copy the Student Factsheet: "Dirty Science" and the Student Worksheet: "Observing Dry Soil Samples".

4. Divide the class into teams of two (or four) students.

Classroom Action

1. Teams. Divide the class into teams of two (or four) students, and explain that today they will play the role of extraterrestrial scientists who are investigating whether there is life on Planet Earth! The scientists have sent a probe to Earth to collect two soil samples.
2. Discussion. Is it alive? Our objective is to see if you can tell by looking carefully with a microscope to see 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. Explain that "Don't Know" is a scientifically acceptable answer. In fact, it is a better answer than an unfounded, wild guess. Sketch this object and try to find out what its attributes are later. Write these categories on the blackboard:
   • ALIVE
   • ONCE ALIVE
   • NEVER ALIVE
   • DON'T KNOW
   Write one or two-word answers on the blackboard while you ask the class "What should you look for to decide if something is alive? Is dead, but was once alive? Was never alive?" Likely answers: movement, familiar shapes.
3. Worksheet. Hand out the Student Factsheet: "Dirty Science" and the Student Worksheet: "Observing Dry Soil Samples". Give each team the two samples of "soil", such as might be scooped up by such an extraterrestrial probe visiting the Earth. The two samples will appear very different. Explain that the probe took these samples in two different locations: one was in a "desert" and the other was in a "forest".
4. Activity. Lab work on dry Earth Sample # 1: Each student should gently pour (not scoop) a small, random part of Earth Sample # 1 on a Petri dish. (Scooping may damage the contents.) Students should label these Petri dishes "Earth Sample # 1". Each student should look at Earth Sample # 1, carefully draw the objects seen on their worksheet, and identify each kind of object as either "Alive", "Dead but Once Alive", "Never Alive", and "Don't Know". Students should be encouraged to look at more than one random part of each soil sample. Lab work on dry Earth Sample # 2: Students should follow the same procedure with the second sample.
5. Demonstration. Show the class the "Demonstration Beakers". Pour dechlorinated water in the beakers. Cover the "desert" soil, Earth Sample # 1, with a few centimeters of water to allow the shrimp to swim when they hatch. Just moisten the "forest" soil, Earth Sample # 2. (Too much water will make it mud, and may drown some of the life.) Explain that this is a form of life-detection experiment. If there are dormant life forms in the soil, water could activate them. The drier sample requires more water.
6. Activity. Each student will carefully return the viewed sample from the Petri dish into the beaker by gently pouring, being careful to replace each sample in the correct beaker. Each student will add dechlorinated water to a sample. Have each student label the watered sample with their name, so that they can retrieve their own sample. Set these submerged samples in the incubation area, under a light bulb; this bulb should remain on all night in order to keep the samples warm enough to have the brine shrimp eggs hatch within 24 hours. (They do not need light, they need heat.) Too much heat will evaporate the water.

The brine shrimp will live at least two days after hatching without food. (Food can be dry yeast.) We suggest that you start this lab on FRIDAY and finish it on MONDAY.

PART TWO

What You Need

For Each Team of Students:

• 1 Eyedropper

For Each Student:

• Student Worksheet: Observing Wet Soil Samples
• Student Worksheet: Soil Sample Analysis

Getting Ready

2. Reassemble the class into yesterday's teams.

Classroom Action

NOTE: Make sure that the brine shrimp have actually hatched before you begin this activity. The brine shrimp can be seen with the naked eye as little glittering red-brown specks that move around. If the shrimp have not hatched, you should delay this lesson for one day if you can. They will probably hatch by then.

1. Optional review. Divide the blackboard into two sections, labeled "Earth Sample # 1" and "Earth Sample # 2". Ask a few students to start drawing and listing Alive, Once Alive, Never Alive, and Don't Know objects seen in their two Earth Samples. Continue this until each team has listed two or three objects. Use the information on the blackboard to clear up any obvious misconceptions, or to steer the students' thoughts in new directions.
2. Worksheet. Hand out Student Worksheets: "Observing Wet Soil Samples" and ""Soil Sample Analysis".
3. Lab work on wet Earth Sample # 1. Each student should use an eyedropper to take a drop of the water from on top of Earth Sample # 1 and put it on a Petri dish. Students should label this Petri dish "Earth Sample # 1" and classify any objects seen as on Day 1. Students should be encouraged to look at more than one random part of each soil sample. They may discover, or need to be told, that if they first darken one half of the dish by covering it with paper or their hand, the brine shrimp will swim to the better lit half of the beaker. Holding a light to one side of the dish also works. If students take their sample from the well-lit half they will see more brine shrimp. The students may also discover or be told to stir the soil sample a little and then look at the water again. This should put a few more objects, including brine shrimp and empty brine shrimp eggs, into view. Lab work on wet Earth Sample # 2. Students should follow the same procedure with the second sample.
4. Have students complete their worksheets and share their data. Hold a class discussion to go over the Soil Sample Analysis worksheets.

TEACHER'S KEY: SOIL SAMPLE ANALYSIS

1. Movement, recognizable shapes (e.g. "worm"), growth.
2. Recognizable shapes (e.g. "worm"), but it is no longer moving.
3. No movement or recognizable shape; crystalline or geometric form; recognizable as a non-living thing (e.g. a glass bead!).
4. Adding water to the soil causing eggs to hatch into brine shrimp. The water "activated dormant life". It was easier to tell that life was present because it made the presence of life obvious: moving, shrimp-shaped animals instead of round non-moving balls.
5. A single close-up photograph would pose problems. We would have to rely upon obvious shapes. (A series of still photographs taken at the same spot could reveal movement from frame to frame.) Color might help; green may indicate chlorophyll.
6. Yes! In both samples, recognizable animals were moving around.
7. No! There was no obvious life in Earth Sample # 1 when it was dry. (The brine shrimp eggs did not look like life.)
8. Life must be abundant on Earth! Two random samples both contained obvious life! Also life on Earth must like water.
9. Earth Sample # 1 is probably most like soil on Mars, as it was much drier and we know that Mars has no liquid water. Also, the topsoil looked organic, which is very unlikely for Martian soil!
10. It might be difficult to find life on Mars. A random sample would be small. and by chance may have no life. It would be a good idea to add water to a Martian soil sample to see if it would activate any dormant life. We know that Mars once had water... maybe some life has survived!

Going Further activities

Sea Monkeys

Fish Out of Water

2. Ordering: An "Instant Fish Kit" using the eggs of the annual killifish Nothobianchius, is available from Carolina Biological Supply. The kit contains instructions. You must specify the delivery date for the eggs; the kit itself only gives you a coupon for the eggs (no extra charge).

2. Activity: Students may add the water to the fish eggs in a Petri dish, and watch the hatching which begins immediately and is complete within 90 minutes. Hand lenses or low power microscopes enhance the experience.

3. Lessons: Students see that even complex life may be dormant until activated with water. They also see an adaptation to a unique environment that is arid for part of the year. Thought question: As a bonus, you may discuss fish life cycles.

4. Caution: Fish are vertebrates, animals with backbones. As such, you must be concerned with any rules that govern the use of vertebrate lab animals at your school.

5. Keeping the Fish: You may plan on keeping the fish in a class tropical aquarium. They mature in a few weeks, grow to about two inches, and eat regular tropical fish food. You may send them home with students, with instructions on their care. They may also be sold to aquarium shops.

The Lotus

2. The Lotus: Eventually inform the students that scientists have taken apparently lifeless lotus seeds from a dry Egyptian tomb. A lotus is an aquatic plant that grew along the Nile River. These seeds were entombed for thousands of years. Explain how dry the Egyptian desert is; Egyptian tombs are bone dry, not musty. When scientists added water, one of the lotus seeds sprouted and grew into a regular lotus plant. Is this the oldest plant on Earth?

3. What If?: Scientists believe that conditions on Mars may have been more favorable to life in the past than they are today. What if life flourished on Mars long ago, and now only a few dormant seeds remain? What if our probe finds such a seed? Could we "activate" it with water?

Instant Algae

Soil Search

The Chia Monster

Adapted from Life: Here? There? Elsewhere?, SETI Institute, Teacher Ideas Press, Englewood, CO, 1(800)237-6124 Return to description of lessons on 1995 CMEX Mars Sampler CD ROM