SUNDAY, MARCH 06, 2011
Is this claim of bacteria in a meteorite any better than the 1996 one?
A new paper from a NASA scientist claims to present evidence for bacteria-like organisms in some meteorites. (Richard Hoover, 2011, Fossils of cyanobacteria in C11 carbonaceous meteorites. Journal of Cosmology 2011, vol 13.)
I don't know much about meteorites, but here's my evaluation:(Executive Summary: Move along folks, there's nothing to see here.)
What the author did:
He fractured tiny comet-derived meteorites (0.1 - 0.6 g) from two events and examined the freshly broken surfaces. He claims to have observed structures that are remnants of cyanobacteria.
These meteorites are of a special very rare type (only 9 are known). They are about 20% water, and soft enough to cut with a knife. They mainly consist of minerals cemented together with magnesium sulfate ('Epsom salts'). They come from asteroids and comets, not planets like the Alan Hills meteorite from Mars. Hooper's reasoning that they come mainly from comets seems reasonable to me.
They contain quite a bit of organic (carbon-based) material, but I don't know if this differs significantly from the polycyclic aromatic hydrocarbons known to be present in comets. It's true that PAHs found on Earth are usually biological in origin (think of the tarry crud that accumulates on your barbeque grill), but that doesn't mean that PAHs from space have biological origins.
An important concern with this kind of study is contamination with terrestrial organisms before examination. He doesn't say how the meteorites have been stored before he obtained them, nor how the surfaces of the meteorites were treated before being fractured and examined. He doesn't say how they were fractured - might they have been cut with a scalpel blade or just pressed on until they crumbled? He says that the tools were flame-sterilized, but not what the tools were or how they were used.
He used two examination techniques. FESEM is field emission scanning electron microscopy - this seems to be a higher-resolution form of scanning electron microscopy (SEM), with the usual risks of artefacts. The fractured surfaces were not coated with anything before being analyzed - I don't know what effect this might have. The other technique is energy-dispersive X-ray analysis - I gather that this is an add-on to SEM that can scan a specimen and report on the abundance of specific atoms at different positions. Its results can be reported as the distribution of atoms at a particular position or as an image of the specimen, shaded to show the varying density of a particular atom.
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Read more here/Leia mais aqui: RRResearch
