You Call This Life?
By Jim Davidson
Special to The Libertarian Enterprise
Recently, a paper by Dr. David McKay and his co-workers gave evidence that Martian bacteria may have lived in the Shergottite, Nakhlite and Chassigny (SNC) meteorite known by its catalog number ALH 84001. Almost immediately, NASA officials began using the paper to promote NASA budget initiatives for Mars exploration. To the surprise of no one, NASA has been successful in convincing many that fossil life on Mars has been conclusively proven. As a result, many Mars exploration projects that might have been zeroed in the most recent budget are now much more sure of funding.
Unfortunately, as Dr. Robert Zubrin explains in his very recent book The Case for Mars, these Mars exploration projects are not entirely certain of success. One of the first of these new projects is Mars Pathfinder, which is relying upon an airbag landing system which Zubrin describes as having an "unblemished record of failure (Zubrin, Robert, The Case for Mars, Free Press, NY, 1996)" to protect its tiny rover capable of venturing many centimeters from the landing site. Zubrin notes, "If the vehicle does not break after it performs several 60 to 100 kilometer per hour bounces along the surface [it will collect] information on the geology and surface chemistry of its landing site (Ibid.)."
As usual, we are relying upon the least reliable sort of entity to carry out Mars exploration on our behalf. Meanwhile, the government-funded research on the subject of fossil life in the SNC meteorite ALH 84001 is nothing if not controversial. Among the more interesting material questioning the findings of McKay, et al, is a paper summarized in the most recent Lunar and Planetary Information Bulletin available for review at the Houston Space Society's Alvin O. Carley Memorial Library. The paper is presented in much greater detail, with hypertext links to many other papers on the same sample of meteorite, at http://www.lpi.usra.edu/pub/lpi/meteorites/mars_meteorite.html on the World Wide Web.
In their paper, McKay et al review the evidence that ALH 84001 and other SNC meteorites are from Mars. They then describe three sets of observations which provide circumstantial evidence of Martian bacteria. "None of these observations is in itself conclusive for the existence of past life. Although there are alternative explanations for each of these phenomena taken individually, when they are considered collectively, particularly in view of their spatial association, we conclude that they are evidence for primitive life on Mars (McKay, David, et al, "Search for Past Life on Mars: Possible Relict Biogenic Activity in Martian Meteorite SLH 84001," Science, 16 August 1996)."
Keep in mind that these researchers do not claim to have found anything as exciting as living bacteria, nor anything more advanced than single-celled bacteria. These aren't even eucaryotic bacteria in that they are not believed to have cell nuclei. They are most definitively not little green men.
In his paper refuting and clarifying much of the evidence on ALH 84001, Dr. Allan H. Treiman of the Lunar and Planetary Institute goes into great detail about various elements of the case for fossil life on Mars. My intention here is merely to summarize some of the highlights for those who may have an interest.
First, there is a critical issue with regard to the identification of SNC meteorites with Mars. Dr. Treiman believes that all 12 SNC meteorites share so many common characteristics with samples analyzed by the two Viking landers that there is "little doubt now that ALH 84001 is from Mars (Treiman, Allan, "Fossil Life in ALH 84001" LPI Bulletin, Summer 1996)." The most compelling evidence is that these meteorites contain traces of gas with composition identical to the Martian atmosphere as analyzed by the Viking landers. The possibilities of extra-Solar System sources, or a highly unusual asteroidal origin for these SNC meteorites cannot be ruled out, but the Martian origin is certainly the simplest of the available explanations.
Second, there is the critical issue with regard to whether ALH 84001 was infiltrated by liquid water while on Mars. There are no life forms known to humans which can form, multiply, or survive in the absence of liquid water. The issue of water infiltration in ALH 84001 hinges on how the carbonate globules inside the meteorite formed. Treiman reports that there is little doubt they formed while on Mars, since they are much older than the meteorite impact event. Water deposition is certainly a possible explanation, but similar carbonate globules are also formed at temperatures in excess of 650 degrees Celsius (1200 degrees Fahrenheit). Given the presumed volcanic origin of this sample, and given the evidence from other researchers (reported in Treiman's article) that the ALH 84001 globules grew at very high temperatures, significant doubt must be cast upon the idea that the observations McKay et al report are evidence of life.
Beyond these preliminaries, there are alternative explanations for all the observations from McKay's group. The microscopic shapes identified as being like Earthly nanobacteria are also created by inorganic processes. Moreover, the paleontologist Dr. W. Schopf notes that ancient bacteria on Earth were hundreds of times larger than the shapes found in ALH 84001 that were supposedly contemporaries on Mars. Why ancient life on Mars should be so tiny in comparison to ancient life on Earth is troublesomely unknown. Schopf also expressed concern that evidence of cell walls, evidence of reproduction, and evidence of growth and formation of colonies were all significantly lacking in the McKay group's observations.
These microscopic shapes may also be an artifact of the sample preparation process for electron microscopy. Coating the sample with gold and palladium was necessary to examine it under the electron microscope. Dr. Treiman reports concern that the supposed biological shapes were produced by the gold-palladium accumulating around much smaller objects.
Additionally, the microscopic shapes may be Earth bacteria that infiltrated the presumably porous (to liquid water in the distant past) material of ALH 84001. Dr. Treiman cautions that the other SNC meteorites examined by the McKay group to rule out Earth bacteria infiltration lacked the carbonate mineral grains that are found with the supposed bacteria. Thus the McKay group seems to have ruled out appleseeds from within oranges, hardly an impressive feat.
Another observation by the McKay group relates to microscopic mineral grains found near the supposed bacteria. These are similar to such grains produced by bacteria on Earth. Dr. Treiman casts doubt on the identification of greigite among the mineral grains, which is associated on Earth with a plant root bacteria. Even if the material identified was greigite, its presence is not easily explained in the absence of plant life. Since the "greigite" grains decomposed during analysis by transmission electron microscope, they cannot be definitively identified.
Other mineral grains included magnetite and pyrrhotite. Earth bacteria will use magnetite mineral grains to align themselves to Earth's magnetic field for navigation purposes. Today Mars has a very weak magnetic field, and it is clear that use of magnetite for alignment would be pointless on Mars today. Planetary magnetic fields do change, but as Treiman comments, "It is completely unknown whether Mars had a magnetic field at the time when the carbonate mineral globules formed (Ibid.)." Non-biological processes produce similar grains, and the arguments McKay's group present for a biological origin of the grains rests on "interpretations of ambiguous textures and minerals (Ibid.)."
Finally, there is the issue of polycyclic aromatic hydrocarbons (PAH). These organic molecules are found in and near the carbonate globules in ALH 84001. An example of a PAH you may be familiar with is naphthalene, the chemical in mothballs. While such chemicals do form in the decomposition of bacteria, Dr. Treiman notes that they are also "abundant in carbonaceous chondrite meteorites (Ibid.)." While these organic molecules almost certainly formed on Mars, there are a very wide variety of non-biological mechanisms for their production. As evidence of a "pre-biotic organic chemistry" on Mars, the PAH chemicals are "Nearly as exciting as proof of life itself (Ibid.)."
The issue of ancient life on Mars will continue to be debated in the scientific community. Given the significant doubts at every level about the observations of the McKay group, it is unlikely that any definitive conclusions will be reached without, at a minimum a Mars sample return mission. A human mission to Mars would seem necessary to conduct the extensive investigations needed to make any conclusive determination.
One may certainly question the McKay group's statement that, given alternative explanations for each of the phenomena, they should be considered together as evidence for life on Mars. That flies in the face of centuries of scientific method. William of Ockham established the rule that entities should not be multiplied unnecessarily. Certainly the non-biological processes for creating the observed phenomena exist on Mars. It is therefore dubious indeed to suggest that any concatenation of otherwise explainable phenomena requires the significant complication of life on Mars to be understood. On the contrary, explaining the observed phenomena by attributing them to biological processes multiplies the number of unexplained entities almost without bound. If life produced the observed phenomena, where did it come from? How did it arrive deep within a volcanic rock? How did it evolve? What ecological niche was it filling? What caused it to die off? These questions are considered by neither McKay's group, nor by Dr. Treiman. Greater application of Ockham's razor is my own particular preference.
Of course, the very grave doubts about the scientific merit of the arguments for life on Mars based on the observational evidence has not prevented the unscrupulous from making unsupported statements about it. President Clinton says "Today, rock 84001 speaks to us across all those billions of years and millions of miles. It speaks of the possibility of life." Clinton describes the evidence as "...another vindication of America's space program and our continuing support for it, even in these tough financial times." National Space Society president Charlie Walker says, "We now have compelling evidence for life beyond our shores and now we have to set sail." Given the analysis above, one must wonder what exactly it is about the evidence that Walker finds compelling or that Clinton finds vindicating.
The fact that the only possible samples of Martian soil were delivered to Earth 13,000 years ago by meteoric bombardment is certainly no vindication of our approach to space exploration. Rather, it ought to be held up as embarrassing confirmation of how little we have accomplished with the billions of taxpayer dollars spent. If anything, the very limited results from the government-sponsored Mars exploration program should encourage Americans to reject any further governmental expenditure in this area. We should, instead, encourage private companies to open the space frontier to exploration, tourism, and economic development. Had we opened the space age with private satellite launches in the 1950s, we would now have thousands of samples of Martian soil under analysis while millions would be travelling through space to various destinations for all kinds of individual purposes.
Instead, we have only the promise of more billions being spent on robotic exploration, with no plans to send humans to Mars in our lifetime. The chances that anyone reading this article will fly to Mars on a government-backed expedition are so trifling as to be dismissed as irrelevant. You deserve better.
Jim Davidson has always been a liberty minded individualist, but got very serious about it after the state shut down his space tourism company, Space Travel Services, in 1991. Jim has a bachelor's in history from Columbia (1985), an MBA in marketing from Rice (1987), has worked in aerospace, software, banking, real estate, and is currently Chief Operating Officer of a $3 million revenues medical company. Among his other interests, Jim has been president of the Houston Space Society and scubas whenever he can.
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