Editor's note: the following is a response provided to SpaceRef by the JSC Mars Meteorite Team (David McKay, Kathie Thomas-Keptra, and Everett Gibson) regarding a paper "Magnetite morphology and life on Mars" (and associated press releases) by Buseck et al. that appears in the 19 November 2001 issue of the Proceedings of the National Academy of Sciences (PNAS).
"Buseck et al. have "rediscovered "an anaytical method developed in 1947 by Dennis Gabor for defining the morphology of crystals using electron microscopy. Unfortunately, the Buseck et al. paper adds nothing to further the understanding of the issue of life on Mars. It demonstrates that these authors fail to understand the work of Thomas-Keprta et al, 2001 who used a transmission electron microscope to image individual microscopic particles at multiple angles and orientations. From this, the 3-D morphology of the particles could be reconstructed. The technique used by Buseck et al. also uses a transmission electron microscope to image microscopic particles at many different angles in order to reconstruct a 3-D image. These two techniques, for this particular application, are essentially identical.
The Buseck et al. PNAS paper is interesting in that they do not examine ALH84001's population of likely biogenically produced magnetite crystals or the reference MV-1 magnetite crystals; these magnetite populations are the central issues in the debate and without studying either population, at best, their conclusions are irrelevant to the question of life on Mars. Buseck et al. describes the 3-D geometry of a magnetite crystal from "an undescribed, uncultured magnetotactic coccus collected from Sweet Springs Natural Reserve, Morro Bay, CA." It is unclear why they would describe just any magnetite from a previously undescribed strain and compare the geometry of one crystal with one of the best described terrestrial magnetite populations, that of strain MV-1. Buseck et al. are trying to compare a quick study of "oranges (i.e., his undescribed magnetites) with a well-defined study of "apples" (magnetites from ALH84001 and MV-1).
Buseck et al. are trying to lay claim to discovering an analytical method of defining morphology of nanocrystals. Such work has been done for decades using conventional TEM techniques. We see no scientific basis for the Buseck et al. comments "we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars" when he has not examined the magnetites in ALH84001 or MV-1.
The statement at the conclusion of the Buseck et al. PNAS contribution is another example of researchers trying to use data to refute a scientific hypothesis when the data does not apply to the arguments. One must consider all the lines of evidence used to reach the conclusions. Furthermore, Buseck et al. state that three of the four lines of evidence proposed by McKay et al. 1996 have been refuted; that is incorrect. Gibson et al. 2001 (in Precambrian Research) show additional evidence to support all the original lines of evidence of possible biogenic activity within ALH84001 and its carbonate globules are valid. Additional evidence for possible biogenic activity was also described for two younger Martian meteorites-Nakhla (1.3 billion years old) and Shergotty (165 million years old) in that same report (Gibson et al. 2001).
The Buseck et al. paper appears to be little more than a poorly disguised advertisement for the technique of electron tomography, an attempt to capitalize on the intense debate surrounding the issue of life on Mars to gain publicity. We have been looking forward to the scientific results from Buseck et al. and were very disappointed.
"Evidence for water and organic compounds on Mars and Europa has astrobiologists seriously pursuing the possibility that primitive life once existed on other planets and moons. As they gear up for the real acid test -- collecting samples from these distant bodies to examine them directly for evidence of life -- they are tackling nothing less profound than the origins of life in the universe."
"Everett Gibson, a NASA researcher who was among the group that first proposed that ALH840001 contained evidence of life, said that Buseck has not even looked at the Mars meteorite. "How can he draw this conclusion without seeing the material?" Gibson asked. He said that other researchers have found evidence that supports the NASA group."