<P> One of the designers of the Labeled Release experiment, Gilbert Levin, believes his results are a definitive diagnostic for life on Mars . Levin's interpretation is disputed by many scientists . A 2006 astrobiology textbook noted that "With unsterilized Terrestrial samples, though, the addition of more nutrients after the initial incubation would then produce still more radioactive gas as the dormant bacteria sprang into action to consume the new dose of food . This was not true of the Martian soil; on Mars, the second and third nutrient injections did not produce any further release of labeled gas ." Other scientists argue that superoxides in the soil could have produced this effect without life being present . An almost general consensus discarded the Labeled Release data as evidence of life, because the gas chromatograph & mass spectrometer, designed to identify natural organic matter, did not detect organic molecules . More recently, high levels of organic chemicals, particularly chlorobenzene, were detected in powder drilled from one of the rocks, named "Cumberland", analyzed by the Curiosity rover . Nonetheless, the results of the Viking mission concerning life are considered by the general expert community, at best, as inconclusive . </P> <P> In 2007, during a Seminar of the Geophysical Laboratory of the Carnegie Institution (Washington, D.C., USA), Gilbert Levin's investigation was assessed once more . Levin still maintains that his original data were correct, as the positive and negative control experiments were in order . Moreover, Levin's team, on 12 April 2012, reported a statistical speculation, based on old data--reinterpreted mathematically through cluster analysis--of the Labeled Release experiments, that may suggest evidence of "extant microbial life on Mars ." Critics counter that the method has not yet been proven effective for differentiating between biological and non-biological processes on Earth so it is premature to draw any conclusions . </P> <P> A research team from the National Autonomous University of Mexico headed by Rafael Navarro - González, concluded that the GCMS equipment (TV - GC - MS) used by the Viking program to search for organic molecules, may not be sensitive enough to detect low levels of organics . Klaus Biemann, the principal investigator of the GCMS experiment on Viking wrote a rebuttal . Because of the simplicity of sample handling, TV--GC--MS is still considered the standard method for organic detection on future Mars missions, so Navarro - González suggests that the design of future organic instruments for Mars should include other methods of detection . </P> <P> After the discovery of perchlorates on Mars by the Phoenix lander, practically the same team of Navarro - González published a paper arguing that the Viking GCMS results were compromised by presence of perchlorates . A 2011 astrobiology textbook notes that "while perchlorate is too poor an oxidizer to reproduce the LR results (under the conditions of that experiment perchlorate does not oxidize organics), it does oxidize, and thus destroy, organics at the higher temperatures used in the Viking GCMS experiment ." Biemann has written a commentary critical of this Navarro - González paper as well, to which the latter have replied; the exchange was published in December 2011 . </P>

Describe the leading hypothesis for how mars lost atmospheric gas