When NASA needed to design an experiment to detect if life still exists on Mars, which the 1976 Viking lander should run, the experiment was carefully conceived and designed. It was intended that if the experiment turns out positive, then there is life. The experiment did turn positive.
But this result was rejected very fast. Ground: it cannot be.
For the general public, the answer to the question of life on Mars evolved gradually to a negative answer:
The fact is, the experiment was positive, and the conceiver of the experiment has been fighting for the last 24 years to re-establish the fact.
In a July 30, 1997 press release, Dr. Gilbert V. Levin, President of Biospherics Incorporated, who was the conceptor of the life detection experiment of the Viking lander, said he has now concluded that his experiment detected microbial life on Mars 21 years ago. Based on a re-evaluation of his and other Viking results coupled with new Martian and Earth relevant scientific data, Levin stated: "The only conclusion consistent with all the known facts is that the Viking Labeled Release Experiment discovered microorganisms in the soil of Mars."
The complete original press release is definitely something to read!
In the 29 July-1 August 1997 scientific report of the Viking LR experiment to detect life on Mars, you can read the following conclusion:
"Many hypotheses have been advanced and tested in attempts to account for the well-characterized activity detected in the surface material of Mars by the LR experiment. As shown above, these hypotheses have themselves been found wanting. The demonstrated success of the LR and the exquisite sensitivity with which it has detected microorganisms during its extensive test program with its record of no false positives can no longer be denied. No non-biological approach published, or known to the author, has duplicated the LR Mars data. Some laboratory experiments have produced positive responses, but the detailed thermal sensitivity exhibited by the variety of controls conducted on Mars has remained elusive in all such tests compatible with Martian conditions. On the other hand, a combination of known properties of microorganisms, perhaps even those possessed by single species, could reproduce all aspects of the LR data. The biological interpretation of the Mars LR results is left standing alone. Recent discoveries of life forms thriving in extraordinarily severe environments on Earth strongly indicate that any alien organisms arriving on Mars might well and widely adapt to their new home. Application of the scientific principle leads to a conclusion: the Viking LR experiment detected living microorganisms in the soil of Mars".
Read the full report is all you need to be convinced.
"The Labeled Release (LR) life detection experiment aboard NASA's 1976 Viking Mission reported results which met the established criteria for the detection of living microorganisms in the soil of Mars. However, a variety of reasons led to the consensus of involved scientists that the positive responses at both Lander sites were caused by a chemical agent in the soil and not by microorganisms. In the years since Viking, new information from Mars and Earth has come to bear on this issue. ... It is concluded that the Viking LR experiment detected living microorganisms in the soil of Mars."
From: ""Proceedings of Spie, SPIE-The International Society for Optical Engineering - Instruments, Methods, and Missions for the Investigation of Extraterrestrial Microorganisms", July 29 - August 1, 1997, San Diego, California.
Any kind of life that got a start on Mars would have slowly evolved by natural selection to keep up with changes in the environment. Life is enormously resourceful, and there is no reason to think that life originating on Mars would be less adaptable than the earth's. If free oxygen were never present in the atmosphere, life could thrive without it. Many of the earth's organisms do. If liquid water became scarce, Martian organisms might have come to retain a supply in their tissues and add to that precious hoard by acquiring other forms of water from the environment. Many common earthly micro-organisms can survive under Martian conditions. Scientists have put samples of soil in containers called "Mars jars", where the atmospheric temperature, composition, pressure and dryness are close to those of Mars. Some of the micro-organisms in the samples always survive.
Subsurface Martian organisms could be supplied with a large energy flux from the oxidation of photochemically produced atmospheric H2 and CO diffusing into the regolith.
Were the Viking probes looking for the correct signs anyway? The chemical reactions that drive biological activity are now known to be much more diverse than anyone suspected in Viking's day. It is now clear that reactions involving hydrogen, methane, sulphur or iron can sustain biological activity. Last year, Todd Stevens and James McKinley of the Pacific Northwest Laboratory in Richmond, Washington, discovered bacteria deep within basalt rock beneath the Columbia River that thrive only on hydrogen. The hydrogen is continually produced by chemical reactions between water and crushed basalt. An ecosystem like this would have been completely invisible to the Viking craft.
