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Classroom Activities

Activity: Is There Really Life on Mars?

Instructional Objectives
Background Information
Time Needed for Activity
Target Grade Level
Materials
Procedures
Web Resources


Instructional Objectives:

Students will -

  1. study the work of scientists and determine how scientists test theories;
  2. construct a model of coacervates, observe its characteristics, and compare them with the characteristics of living cells;
  3. infer conditions that may have led to the formation of life.


Background Information:

Is there really life on Mars? Was there once cellular material on the red planet? Scientists have been studying these questions for a long time, and now they have some new information that may give some clues. Scientifically speaking, to study the controversy about life on Mars, it is important to understand what the work of scientists is all about. How do scientists develop a theory like life exists on Mars?

The easiest way to test the theory of life on Mars is to create a series of predictions that can be tested experimentally. If the tests support the predictions, then the theory will gain support; if the tests are inconclusive or do not support the predictions, then the theories will lose support.

Two of the essential scientific questions are what is life, really, and how did it begin? Scientists predict that on primitive Earth, the atmosphere consisted mostly of ammonia, water vapor, methane, and hydrogen. With exposure to intense heat, ultraviolet light, electrical storms, and other conditions, organic molecules conbined to form membrane-bound droplets call coacervates. These may have been the precursors of the first living cells on Earth. If Mars could support life in its early history, then life probably formed on many other planets, too.


Time Needed for Activity:

One period in class to complete the analysis of the Mars evidence scenario. Homework time to write a report describing the research plan. One period in class to make and observe coacervates.


Target Grade Level:

High School


Materials:

Students will work in groups of two or four. Each group needs the following materials: For the coacervate lab:


Procedures:

Part A. Is There Really Life on Mars?

Scientists have been studying this question for more than 25 years, and they have made many observations. Read the summary paragraphs and answer the analysis and conclusion questions.

In the 1970s, the Viking mission to Mars provided information about the geology and weather on the red planet. The primary mission of the two robot space crafts was to determine if there was life on Mars.

Conditions on Mars were thought to be far too harsh for large life forms. There is no liquid water on Mars and the atmosphere is very thin. During one day, the temperature on Mars may range from 10 degrees C to -80 degrees C. The large changes in temperature produce strong winds and planet-wide dust storms. Because of these conditions, scientists decided to look for microorganisms rather than large life-forms.

The Viking spacecraft conducted several experiments. In one experiment, samples of soil were taken from different locations. The soil samples were put into a nutrient broth that supported the growth of microorganisms on Earth. The amount of carbon dioxide in the broths was tested over a period of time.

Scientists were excited to discover that Martian soil produced carbon dioxide in the nutrient broth. However, the amount of carbon dioxide produced in the Martian soil was much smaller than the amount that would be produced by living things on Earth. The results of the Viking spacecraft experiments are not conclusive. Scientists were still not sure if life existed on Mars.

The Viking mission did not return a Mars rock sample to Earth. To study Mars rocks, a team of scientists at NASA Johnson Space Center and at Stanford University have been studying meteorites from Mars. The meteorites are igneous and have been collected on the Earth from 1815 to 1995. They all contain similar minerals, and many show evidence of interactions with liquid water. Because the Martian meteorites are all igneous rocks, they do not tell us as much about the Mars atmosphere and water as we could learn from studies of sediments and soils.

One meteorite has some carbonate globules in it that look like ancient Earth fossils. These blobs, called carbonate rosettes, have cores filed with manganese and surrounded by iron carbonate the then by an iron sulfide layer. Bacteria in ponds produce similar rosettes. Organic chemicals, PAHs (polycyclic aromatic hydrocarbons), were found that could have been formed by primitive bacteria. Electron microscopes have also revealed tiny, teardrop-shaped crystals of nagnetite and iron sulfide. Certain bacteria can manufacture similar crystals. The pictures of the globules look like tiny fossilized nannobacteria, which may be similar to early Earth bacteria.

After reading the summary of the information, have students do the following:

  1. Make a list of each piece of evidence that the scientists have discovered.

  2. From your understanding of the evidence, determine what predictions scientists have made.

  3. Select one hypothesis or prediction and design the imaginary experiment or research projects that you think should be conducted to subject the prediction to scientific testing. Make certain that your proposal is realistic, and decide what evidence you would want to collect. (It is not possible to go back in time or travel at warp speed.)

Have students complete a "Think About It" reflection in their science journals. Discuss their proposed experiments as a class. Predictions have no value unless they can be tested with scientific experiments or checked with existing evidence. Additional resources can be found in the May 1997 issue of Discover Magazine: The Coming Age of Exploration and in "Bugs in the Data?" by Gibbs, W. and Corey S. Powell, Scientific American, October 1996, pp.20-22.

If you want to find out more information write to Antarctic Meteorite, Mail Code SN2,NASA Johnson Space Center, Houston, TX 77058.

Part B. Coacervates: The Beginning of Life?

  1. Work in pairs and wear safety goggles. Pour the gelatin solution into the test tube and add the gum-arabic solution. Stopper the tube, mix gently, and do not shake.

  2. Remove the stopper, remove a drop of the liquid, and test its pH. Record any observations about the liquid in the tube.

  3. Place 1-2 drops of the mixture onto a microscope slide, add a coverslip, and look for coacervates under low power. Observe the coacervates under high power and make drawings of what you see.

  4. Add 2 drops of hydrochloric acid (BE CAREFUL, HYDROCHLORIC ACID CAN BURN YOUR SKIN) to the test-tub mixture and when it clears, prepare a new wet-mount slide as you did before. Before you add the coverslip, add a small drop of dilute food coloring and look for coacervates once again both under low- and high-power magnification.

  5. Record observations and make drawings.

  6. Look at prepared slides of bacteria and single-celled protozoans.
Questions:
  1. What is the relationship between pH and the formation of coacervates?

  2. What conditions in ancient oceans may have caused coacervates to form?

  3. Compare and contrast the prepared slides of cells with your observations of coacervates.

  4. If life is found on other planets, would it be similar to or different from life here on Earth? Explain your answer.
Reference: This observation activity is based on the labs in Addison-Wesley's Biology Laboratory Manual and Prentice Hall's Biology Laboratory Manual.


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