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MARS LIFE: DEBATE GOES ON
By Sean Henahan, Access Excellence 
ATHENS, Ga- (3/21/97) Sophisticated isotopic analyses appear to
support the notion that the unusual Martian meteorite ALH 84001 does contain
signs of life, according to new studies.
Photo: A close up of one of the carbonate globules that was subjected to isotopic analyses. The meteorite was found in Antarctica some 13 years ago. The scientists believe it was formed on Mars 4.6 billion years ago and may have become covered with microorganisms between 3.6 billion and 4 billion years ago. The researchers believe that about 16 million years ago, a comet or asteroid struck the Martian surface and blasted pieces of rock into space, where they drifted for millions of years. The meteorite, found in Antarctica in 1984, fell to Earth about 13,000 years ago. When researchers first announced the discovery of apparent microfossils on a meteorite from Mars last year, skeptics were quick to challenge the findings. The primary objection was that conditions on Mars suggested by the condition of the meteorite were simply too hot to support life, and that carbon globules found on the rock could have been formed by geologic processes. "We felt confident that some parts of this study could be solved in a relatively short time frame, and this is one of those issues," said Dr. Christopher Romanek of the University of Georgia's Savannah River Ecology Laboratory in Aiken, S.C. "This work supports our earlier interpretation for a low-temperature origin of the globules." Romanek was one of the researchers who published the original controversial article in Science. Romanek and colleagues have now re-tested the rock using a technique known as secondary ion mass spectrometry (SIMS). This technique offered a major advance over earlier analyses of the meteorite. The SIMS analysis technically allows for in situ analyses of oxygen and carbon isotope ratios in extremely small samples of carbonate and silicate minerals. These measurements are then correlated with chemical, spatial and textural information. The research team developed a SIMS technique specifically for the Mars rock project. The ion microprobe uses a beam of high-energy plasma to burn tiny craters on the surface of a sample, in this case a polished sample no bigger than a grain of rice. The vaporized material is held in a vacuum and drawn into a mass spectrometer for isotopic analysis. "In our previous measurements, we had to measure hundreds of globules at a time. With this instrument carbonate globules can be studied individually," said Romanek. While other recent studies have suggested a high-temperature origin for the carbonate globules in ALH8401 of up to 650 degrees centigrade, the SIMS test suggests a potential formation temperature of less than 300 degrees C. Romanek believes it may have been cool enough for microscopic life to have flourished. However, he does not discount the possibility that future studies could provide a convincing alternative explanation for the formations found inside the meteorite, but for now, he believes the original conclusions of the study still offer the best explanations. "Everything we see is consistent with biological activity, but I still wouldn't rule out low-temperature inorganic processes as an alternative explanation," added colleague John W. Valley, a University of Wisconsin-Madison geochemist . "We have not proven that this represents life on Mars, but we have disproven the high-temperature hypothesis." Valley said the high-temperature origin hypothesis relies on a set of thermodynamic assumptions that don't measure up on Earth, and therefore don't apply to an ancient Mars that may have had conditions more conducive to life. "If the same assumptions are applied to the carbonates found in the Earth's oceans, one would erroneously conclude that the water temperatures are over 1,000 degrees Fahrenheit and the surface pressures are several thousand atmospheres," Valley said. "These carbonates in the meteorite are easily explained by low-temperature processes similar to those commonly found on Earth," he said. The advantage of the ion microprobe, said Valley, is that it allows for minuscule amounts of material to be sampled, one million times less than would typically be necessary. Employing the microprobe, Valley and his colleagues were able to look deep within the carbonates themselves and make the first in situ measurements of the controversial globules. "Making these analyses in situ has never been done before," he said. "For the first time, we can actually see what we analyze." The team measured the ratios of two different isotopic species of oxygen and two of carbon. They found that the carbon ratios in the meteorite are higher than in Earthbound rocks. This finding helps rule out the idea that the Martian meteorite became contaminated when it hit the Earth. The researchers also observed that oxygen isotopes were not evenly distributed within the sample, lending some support to an organic origin. The life on Mars hypothesis has been challenged on the grounds that the carbonates formed in chemical equilibrium above 1200 degrees Fahrenheit. The new data prove that the meteorite is not in isotopic or chemical equilibrium. "I think that one thing we can all agree on at this point is that it is really too early to come to a final conclusion about life on Mars. We're still in the discovery process for this," commented Douglas Blanchard, chief of the earth science and solar system exploration division at the Johnson Space Center, speaking at a press conference in Houston. "There is no self-consistent evidence to suggest such a high-temperature genesis," said Valley. "All of the chemical, mineralogical and isotopic evidence that we present is consistent with a low-temperature origin." Some 50 labs throughout the world are now working on the Martian meteorite conundrum. Commentators note that even if the high-temperature theory is disproved, it doesn't prove the existence of the microfossils beyond a doubt. Other note that even if the rock turns out to be quite lifeless, it doesn't mean there was never life on Mars. The research appeared in Science, March 14, 1997. Related information on the Internet
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