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Slide 9 of 16
A positive response to any one of the three life detection experiments could have been evidence for life even with negative results to the other two. This was because each experiment tested for a particular type of metabolic activity that possible Martian microorganisms might or might not possess.
One experiment called the Pyrolytic Release (PR) Experiment, designed by Norman Horowitz, showed a response for soil samples but the response occurred in heated as well as unheated samples. If the response had been the result of biological metabolism of microorganisms in the soil then these microbes would have been killed by the heating and the response would not have occurred in heated samples. Therefore, it was more likely that a chemical agent in the soil had caused the response since a simple inorganic catalyst would not have been greatly affected by heating. However, another experiment called the Labeled Release (LR) Experiment, Designed by Gilbert Levin, was positive only for unheated samples but negative for heated samples, suggesting that microorganisms were present in the Martian soil.