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... ite burning up upon entry into the earth's atmosphere vaporizing PAHs near the surface. "No PAHs were found in the meteorite's exterior crust, but the concentration of PAHs increased in the meteorite's interior to levels higher that ever found in Antarctica" Also the concentration of PAHs is greater that what would have been in the atmosphere at the time impacted. Again this makes the source more likely to be extraterrestrial. PAHs that occur in other meteorites within the galaxy their source is inorganic. Investigation with these meteorites and found that concentrations and the types of PAHs found in them were not similar to those found in ALH 84001. If they had been it would suggest that the PAHs in ALH 84001 had been formed by the same inorganic process, but since they are not this could be interpreted as meaning they formed by another process, such as bacterial decay.
The PAHs in ALH 84001 were also similar to those produced by bacterial decay on earth. Again there are limitations to these findings. It is possible that the PAHs on Mars may have originated from a source in space not sampled, for instance. This would lead to a false impression. However this evidence is very suggestive that the PAHs originated on Mars and could be from an organic source such as bacterial decay. The final pieces of evidence are the shapes within the carbonate grains, which closely resemble fossils of bacteria.
Found within the fracture of the carbonate mineral globules and are long, tabular, rounded and almost 'sausage' in shape. They are very small and can only be seen with an advanced electron microscope. If these features are the remains of fossilized bacteria, then this had to be proved as it was possible they could have formed from some inorganic process, or they may not actually be from Mars and be terrestrial, having entered ALH 84001 when it was in Antarctica. Many bacteria on earth were obtained which are similar in shape and size to those found in the Mars meteorite.
Such bacteria also can be found in rocks and are often found in extreme environments. Then it makes it possible that the structures could be fossilized bacteria. It is also possible that the features could be a result of the preparing of the rock for thin section under the electron microscope. This could be many things such as glue, residue or metals used to coat the sample. "SEM generally requires that the sample be coated with a thin film of metal so that the SEM's electrons do not charge the sample and fuzz up the view.
But coating samples with such metals, including the gold-palladium mixture usually can change texture, round off shapes and even create segmentation like the worm's" In order to disprove this possibility, other rocks samples were prepared, not containing the bacteria structures, in the same way ALH 84001 was prepared. Upon examination of these slides, no features, which resembled bacteria, could be seen and there the structures must not have been preparation errors and are actually part of the rock. It was also possible that the shapes were the remains of terrestrial bacteria, as they did resemble bacteria found within other rocks. "The analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of Earth's crust" Other meteorites from Antarctica were looked at for evidence of bacteria, which would be terrestrial; it would be likely that the structures in ALH 84001 would also be terrestrial in origin. None could be found and it is probable that the structures in ALH 84001 are extraterrestrial.
Despite these findings and conclusions, it is still possible that the structures are not Martian bacteria fossils. They could be the result of inorganic processes, and they do not show any real evidence that they were once living, such as cell structures or being in the reproduction stage. It is also still possible that they are the remains of earth bacteria that somehow entered ALH 84001 but not the other meteorites, for reasons such as unsuitable chemistry. Therefore, the presence of these structures in ALH 84001 is not sufficient to prove that life once existed on Mars. There are good evidence that prehistoric life may have once existed on Mars in the form of bacteria.
However, this does not show that life now exists ALH 84001 or on Mars. These findings are very controversial and debatable, with other reasons for formation and occurrence. It is very possible that these findings were lots of coincidences that give the false impression that life once existed. This is the best evidence ever found for the existence of extraterrestrial life and although the chances are far off, it is possible. The findings have evoked great interest into Mars and with more research and money going into the investigations an absolute conclusion can be provided about finding out if life did once exist on Mars. At this time there is no definite answer to whether the findings on the ALH 84001 are significant signs of life or there was life on Mars at one time.
We will have to wait until humans or robots go there and test samples directly or bring them back to Earth for analysis. Till then there is no way to actually prove the findings from the ALH 84001. Works Cited Beatty, Kelly. "Messenger from Mars (meteorite ALH 84001). " Sky & Telescope July 1997, v 94: 36 - 41. Chain, Andrew. "Life on Mars: the great debate. " Popular Science July 1997, v 251: 60 - 66.
Cowen, Ron. "Meteorite still holds inklings of life (Martian meteorite ALH 8001). Science News March 29, 1997, v 151: 190 - 191. Kerr, Richard. "Martian 'microbes' cover their tracks. " Science April 4, 1997, v 276: 30 - 31. Kerr, Richard. "Martian rocks tell divergent stories. " Science November 8, 1996, v 274: 918. Kerr, Richard. "Possible glimpse of earth-like geology in Mars rock. " Science August 1, 1997, v 277: 638 - 639. Kerr, Richard. "Putative Martian microbes called microscopy artifacts. " Science December 5, 1997, v 278: 1706 - 1707.
R. C. "Life on Mars: Take two (minute spherical and rod-shaped features identified on Mars). " Science News May 1, 1999, v 155: 286. River, R. "The chemical composition of Martian soil and rocks returned by the mobile alpha proton X-ray spectrometer: Preliminary results from the X-ray mode. " Science December 5, 1997, v 278: 1771 - 1774.
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