show activity similar to the first response, that was evidence that the activity was chemical in nature. However, a nil, or greatly diminished response, was evidence for biology. This same control was to be used for any of the three life detection experiments that showed a positive initial result. The initial assessment of results from the Viking 1 PR experiment was that "analysis of the results shows that a small but significant formation of organic matter occurred" and that the sterilized control showed no evidence of organics, showing that the "findings could be attributed to biological activity." However, given the persistence of organic release at 90 °C, the inhibition of organics after injecting water vapor and, especially, the lack of detection of organics in the Martian soil by the GCMS experiment, the investigators concluded that a nonbiological explanation of the PR results was most likely. However, in subsequent years, as the GCMS results have come increasingly under scrutiny, the pyrolytic release experiment results have again come to be viewed as possibly consistent with biological activity, although "An explanation for the apparent small synthesis of organic matter in the pyrolytic release experiment remains obscure." Scientific conclusions Organic compounds seem to be common, for example, on asteroids, meteorites, comets and the icy bodies orbiting the Sun, so detecting no trace of any organic compound on the surface of Mars came as a surprise. The GC-MS was definitely working, because the controls were effective and it was able to detect traces of chlorine, attributed to the cleaning solvents that had been used to sterilize it prior to launch. A reanalysis of the GC-MS data was performed in 2018, suggesting that organic compounds may actually have been detected, corroborating with data from the Curiosity rover. At the time, the total absence of organic material on the surface made the results of the biology experiments moot, since metabolism involving organic compounds were what those experiments were designed to detect. The general scientific community surmises that the Viking's biological tests remain inconclusive, and can be explained by purely chemical processes Despite the positive result from the Labeled Release experiment, a general assessment is that the results seen in the four experiments are best explained by oxidative chemical reactions with the Martian soil. One of the current conclusions is that the Martian soil, being continuously exposed to UV light from the Sun (Mars has no protective ozone