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!
THE SCIENTIFIC REPORT:
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.
full report is all you need to be convinced.
THE SPIE STATEMENT:
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."
Reprinted from: Proceedings of Spie, SPIE-The International Society for
Optical Engineering, "Instruments, Methods, and Missions for the Investigation
of Extraterrestrial Microorganisms. 29 July-1 August 1997, San Diego, California.
THE CONDITIONS ISSUE:
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.
LIFE AS WE KNOW IT?
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.