QUESTION:
We have set up a test to measure the pressure change to sealed soil +
nutrient samples over time. We found that the sterile one did not change
pressure (measured over days with a datalogger), but the "normal" earth
soil one did. Do you have similar results for soil testing from Mars
missions? I set this up with my class because I thought that was how 
the microbe test was / might have been done. I can't find any data on 
the website and have
checked the FAQ's. Do you have pressure v time data for sealed Mars soil +
nutrient and if so, where could we get it to compare to our results. I
would also imagine that a simple chemical reaction would produce gras, but
this curve should be more linear than that caused by microbes.

ANSWER from Nathan Bridges on October 18, 1999:
Interesting question.  I am not an expert in this area, so I got some
help in answering it from my office mate, Albert Yen.  The Gas EXchange
experiment on the Viking Landers (GEX) was designed to measure the
decomposition of indigenous and added compounds by measuring the uptake or
release of various gasses.  GEX measured the composition of gasses using a
gas chromatograph.  Soil samples were wetted by either water vapor or an
aqueous nutrient.  The water caused desorption of CO2, Ar, and N2 whereas
O2 was released due to the inferred decomposition of superoxides.  The mean
composition of gasses measured was 96.2% CO2, 2.3% N2, 1.5% Ar, and æ 0.15%
O2.  When the same sample was recharged (i.e., the experiment run again on
the same soil), only CO2 was given off.

I am not familiar enough with this experiment to know if there is
pressure data.  I suggest you find the following reference and then do a
literature search based on citations in it and later work by the same
authors: Oyama, V.I. and B.J. Berdahl, The Viking Gas Exchange Experiment
results from Chryse and Utopia surface samples, J. Geophys. Res., 82,
4669-4680, 1977.