Obstacles raised against acceptance of the LR data as proof of life, and the problems with each follow:
a.Failure to detect organics. The Viking organic analysis instrument (GCMS), an abbreviated gas chromatograph-mass spectrometer designed to identify the organic material widely presumed to be present on Mars, found no organic molecules. Based on this result, the strong consensus of the space science community was that the LR positive responses were not of biological origin. However, the GCMS Experimenter disclaimed his instrument as a life detector, saying as much organic matter as in 1 billion bacterial cells were required for a result. Subsequently, it was reported that several problems with the GCMS flight-type instrument further depleted its sensitivity. Upon announcing the detection of organic matter in the ALH4001 Martian meteorite, a NASA official explained that the Viking GCMS had not been sensitive enough to detect the level of organics found by the full-scale GCMS instrument by which the Martian meteorite was analyzed. It has also been shown that the temperature applied in the Viking GCMS fell short of that needed to vaporize some heat-stable organic molecules in living cells, which, it was claimed, could explain the failure of the Viking GCMS to detect organic matter. Corrections designed to fix this problem, and to provide greatly increased sensitivity have been incorporated into newly designed planetary probe GCMS instruments. It is interesting to note that Viking, itself, produced evidence that organic matter is constantly forming on Mars, and is not destroyed by a strong oxidant. The Pyrolytic Release (PR) experimenters reported "The data show that a fixation of atmospheric carbon occurs in the surface material of Mars under conditions approximating the Martian ones." In the experiment, Martian soil was exposed to simulated Martian atmosphere containing labeled CO2 and CO. After 120 hours, any non-fixed carbon gas was driven off by heat. Then, upon heating the soil to pyrolysis temperature, any carbon that had been fixed was vaporized into the headspace. Statistically significant amounts of labeled carbon gas were evolved from the Martian soil, providing evidence that fixation had occurred (but in insufficient amount to support a claim for biology). The formation and the persistence of the organic matter throughout the length of the experiment are evidence against the presence of the oxidant(s) or any other characteristic of the soil that would destroy all traces of organic matter. The PR Experimenters reported "Our findings suggest that UV presently reaching the Martian surface may be producing organic matter . . . the amount of product found could be considerable over geologic time."
b.Strong Oxidant. When, as stated above, sampling soil from under a rock on Mars demonstrated that UV light was not responsible for the apparent absences of life and organic matter, the presence of hydrogen peroxide and/or other strong oxidant(s) in the soil was proposed instead. This hypothesis was made despite findings by the Viking Magnetic Properties Experiment (Figure 7) that the surface material of Mars contained a large magnetic component, evidence against a highly oxidized condition. The authors of the Viking Magnetic Properties paper concluded: "The possibilities as to the nature of the magnetic particles detected on Mars are here summarized. Some or all could be (1) highly magnetic, unoxidized mineral grains (metallic Fe, magnetite, pyrrhotite) forming the core beneath a reddish coating of limionite or hematite;" and added several lesser possibilities, none of which could render the surface material highly oxidizing. The evidence against an oxidant provided by the PR, discussed immediately above, was also disregarded by the pro-oxidant theorists. Since Viking, two Earth-based IR observations, by the ESA orbiter and, most recently, data from the Rover Opportunity (Figure 8) have shown Mars surface iron to be not completely oxidized (ferric), but to occur mostly in the ferrous form. Thus, it is difficult to make a case for the existence of an ubiquitous strong oxidant that destroys all organic matter on the surface of Mars, or even its presence at both Viking landing sites to account for the LR positive results.c. "Too much too soon." The LR positive responses, and the reaction kinetics were said to be those of a first order reaction, without the lag or exponential phases seen in classic microbial growth curves, all of which argued for a simple chemical reaction. However, Figure 9 shows terrestrial LR experiments on a variety of soils which produced response rates with the kinetics and the range of amplitudes of the LR on Mars.
d.Second Injection. Second injections of nutrient produced no new evolution of gas, but, instead, quickly reduced the amount of gas accumulated from the first injection by about 20%. Although 2nd injection responsiveness was not part of the LR life detection criteria, the lack of a new surge of gas upon injection of fresh medium was subsequently cited as evidence against biology. However, a test of bonded, NASA-supplied Antarctic soil No. 664, containing less than 10 viable cells/g, showed this type of response to a 2nd injection as seen in Figures 10a and 10b. (The high initial cpm of the sterile Antarctic soil reflects residual gas in the test cell used. This does not interfere with the demonstration of the effect of the 2nd injection.) Thus, the failure of the 2nd injection to elicit a response can be attributed to the organisms in the active sample having died sometime after the 1st injection, during the latter part of Cycle 1. The effect of the 2nd injection was to wet the soil, causing it to absorb headspace gas. The gradual re-emergence of the gas into the headspace with time seems to have occurred as the system came to equilibrium.
e."No liquid water, no life." This contention is the primary one now cited by those not ready to accept the discovery of life by Viking's LR. However, Viking, itself, gave strong evidence of the presence of liquid water when the rise in the temperature of its footpad, responding to the rising sun, halted at 273o C. Snow or frost is seen in Viking images of the landing site (Figure 11).
Together, these observations constitute strong evidence for the diurnal presence of liquid water. Theoretical modeling, and direct experimental evidence has been cited that demonstrated liquid water occurring under Martian conditions. Odyssey has shown that much of Mars, including the two Viking landing sites, contains moderate to large amounts of hydrogen (interpreted as water, but called "ice"), much more than found in the Death Valley LR tests, within several centimeters of the Martian surface. Pathfinder has shown that the surface atmosphere of Mars exceeds 20o C part of the day, providing transient conditions for liquid water. The Spirit and Opportunity Rovers have taken images that suggest moist soil as seen in Figure 12. In explaining the stickiness of the soil, MER scientists have said that it "might contain tiny globules of liquid water," or "might contain brine".
Other images of Mars, such as Figures 13 and 15c, show current, if intermittent, rivulet activity. The mounting evidence for liquid water on Mars has resulted in an emerging belief that there may be pockets of liquid water beneath the surface, constituting oases for life. However, there is no support of the life oases theory on Earth. Virtually the entire surface of our planet is inhabited by living microorganisms. NASA, despite declaring its "follow the water" route to finding life on Mars, has not sent a liquid water detection instrument there. Indigenous microorganisms have been found growing on the Earth's South Polar Cap, as seen in Figure 14, and within permafrost in the Arctic. However, there is liquid water even in those frozen places. Very thin films of liquid water exist among the interstices of ice and minerals, enough to sustain an ecology of those highly evolved species.
Desert Varnish. In 1979, the author's attention was called to the possible presence of desert varnish on some of the Martian rocks. Desert varnish had been reported  as being of microbial origin or containing products produced by microorganisms. Since then, many additional articles,,, have commented on the causal relationship between desert varnish and microorganisms. Details of the formation and composition of rock (desert) varnish and its specific potential relevance to extant life on Mars have been described. Figure 15 shows what appears to be desert varnish on rocks at a Viking landing site. A recent news article reports rekindled interest in desert varnish as evidence of life on Mars.
Circadian Rhythm. Re-examination of the kinetics of the LR Mars response indicated a possible biological component. It has been proposed, that the kinetics of evolution of labeled gas in the Viking LR experiment might be attributed to circadian rhythm, a universal biological phenomenon of all known living organisms. While indications of circadian rhythm were detected in the Viking LR data, they did not reach the point of strong statistical significance in the two papers cited. However, another paper , using a non-linear approach, concluded, "Our results strongly support the hypothesis of a biologic origin of the gas collected by the LR experiment from the Martian soil." Additional work is underway to verify statistical significance for that conclusion.
Atmospheric Indicators. Adding to this rising tide of facts supporting the detection of life by the Viking LR experiment are the recent findings in the Martian atmosphere of methane, formaldehyde, and, possibly ammonia,,,, gases frequently involved in microbial metabolism, and, therefore, possible indicators of life. The methane occurred in amounts not deemed adequate for replacement of this short half-lived, UV-labile gas since volcanic activity, a potential non-biological source of methane, has not been indicated by thermal mapping of the entire planet. In the Earth's atmosphere, methane is sustained primarily by biological metabolism. Moreover, the methane detected on Mars was associated with water vapor in the lower atmosphere, consistent with, if not indicative of, the possibility of extant life.