Levin's hypothesis, about the active nature of the martian soil
According to Gilbert Levin, the activity detected in the Viking soil samples by all three biology experiments is best understood in terms of the metabolism of living organisms. This puts him squarely at odds with the majority view that oxidizing chemicals on the surface can provide an adequate explanation (see Oyama's hypothesis, about the active nature of the martian soil). Levin favored a biological interpretation of the Viking results from the outset. But over the years since the mission ended, he has become increasingly outspoken on the issue and, together with his Viking team member, Patricia Straat, has made some remarkable and controversial claims. One is that the Viking gas chromatograph-mass spectrometer (GCMS), which failed to find any sign of organic matter in the martian soil, was much less sensitive than officially stated and would have been incapable of detecting biological matter in samples containing a low density of microorganisms. Another of Levin's claims is that greenish patches, seen on some of the Viking photographs, changed over time, suggesting that they were some kind of plant life, and furthermore, that spectral analysis of the patches compared favorably with the spectra of lichen-bearing rocks on Earth. Opponents of Levin, point out that as an engineer who set out to design an instrument to prove that there was life on Mars, he has an intrinsically biased viewpoint. Further analysis of the Martian soil, over the next few years, should reveal who is right.