December 4 Nature article offers point-counterpoint approach to controversy
The famous Martian meteorite, ALH84001, contains no biological life forms, according to a Case Western Reserve University researcher and colleagues.
The team issues this report in the December 4 issue of Nature, duplicating the methods of a team of scientists from the Johnson Space Center and Stanford University. In rare counterpoint writings in the "Scientific Correspondence" section, Nature allowed the Johnson Space Center team to respond to the group's findings. This paper also appears in the December 4 issue.
CWRU's Ralph Harvey, senior research associate in the Department of Geological Sciences, was on the research team. The lead researcher on the paper was John Bradley from MVA Inc. and the School of Material Science and Engineering at Georgia Institute of Technology. The third researcher is Hap McSween from the University of Tennessee.
The trio reports that most of the purported nanofossils or "worm-like images" are nothing more than lamellae, or fractured surfaces of pyroxene and carbonate crystals.
Last year, the Johnson-Stanford team announced it found evidence of nanofossils in the meteorite. Reports of life on Mars spurred the July 4 mission to Mars to look for further evidence of life.
Allan Hills 84001 -- a meteorite the size of a potato -- remains in the center of a spirited controversy about the possibility of life on Mars. The meteorite was found in the 1980s in Antarctica by the National Science Foundation's Antarctic Search for Meteorite Program (ANSMET), headed by Harvey with headquarters at CWRU.
A Web page offers details on ANSMET, including a link to more information on the meteorite. To view these resources, visit http://www.cwru.edu/artsci/geol/ansmet/index.html.
Harvey, who is currently on his annual expedition to Antarctica to collect meteorites, commented before leaving November 21 that the Johnson-Stanford team has always argued that they had used different techniques to study the meteorite.
Bradley, Harvey, and McSween published a paper last year in Geochimica et Cosmochimica Acta (GCA), announcing that what the other researchers observed was formed geologically, not biologically. The Johnson-Stanford group also announced that these nanofossils were lying on the surface of the meteorite.
In the first GCA study, which used transmission electron microscope imagining (TEM), the researchers found non-biological magnetite whiskers on or near the surfaces of the carbonates. Superficially the whiskers look like worms, but in fact they have nothing to do with biological processes, according to Harvey and colleagues.
The latest study took place over the past six months as the researchers re-examined the meteorite using the new techniques. This time they found yet another population of worm-like forms that are actually mineral lamellae formed by non-biological, geological processes. The lamellae look like worms or nanofossils, but when the specimen is tilted and viewed from another angle, it clearly shows that the lamellae are attached and part of the mineral surfaces.
"The surface topography is highly irregular on a nanometre scale, with emergent lamellae following the major cleavage direction of the substrate," Bradley writes in the paper. The researchers have published pictures of the TEM images to support their findings.
"Peculiar surface structures or segmentation on the worm-like forms are artifacts from conductive metal coatings applied to the samples for imaging in the electron microscope. This is not the first time metal coating artifacts have lead to misidentification of nanofossils in rocks," Bradley said.
"We have now found two different types of mineral forms in ALH84001 that look just like nanofossils, but they are strictly non-biological origins. Sometimes even nature has a perverse sense of humor," he added.
Harvey stressed that during this latest study, the team was careful to use exactly the same methods as the Johnson-Stanford group to lay to rest any arguments that the research methods had affected the findings.
The worm-like mineral lamellae are commonly found at the fractured surfaces of planar crystals. Harvey noted that lunar rocks -- in which there has been no evidence of life found -- contain these same formations.
Does this put an end to the life on Mars debate? "We haven't driven the final nail in the coffin yet about organisms in this Martian rock, but our latest article offers a lot of insight that shows these fractures zones in the rock are incredibly complex," Harvey said, "and that it is very dangerous to try to draw any hypothesis from a few pictures from here or there."
Materials provided by Case Western Reserve University. Note: Content may be edited for style and length.
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