Good news from NASA...
Well, that was then and this is now. Work has continued on the meteorite and NASA recently announced that the new conclusions are... well... pretty much the same as the old ones, only better:
The new research focused on investigating alternate proposals for the creation of materials thought to be signs of ancient life found in the meteorite. The new study argues that ancient life remains the most plausible explanation for the materials and structures found in the meteorite.
In 1996, a group of scientists led by David McKay, Everett Gibson and Kathie Thomas-Keprta of NASA’s Johnson Space Center (JSC) in Houston published an article in Science announcing the discovery of biogenic evidence in the ALH84001 meteorite. A newly published paper revisits that original hypothesis with new analyses. The paper, “Origin of Magnetite Nanocrystals in Martian Meteorite ALH84001,” by Thomas-Keprta and coauthors Simon Clemett, McKay, Gibson and Susan Wentworth, all scientists in the Astromaterials Research and Exploration Science Directorate at JSC, is in the November issue of the journal Geochimica et Cosmochimica Acta of The Geochemical Society and The Meteoritical Society.
Magnetite crystals in ALH84001 have been a focus of debate about the possibility of life on Mars. Magnetite is an iron-bearing, magnetic mineral. On Earth, some water and soil bacteria secrete the mineral within their cells. The 1996 study suggested that some magnetite crystals associated with carbonate globules in ALH84001 are biogenic because they share many characteristics with those found in bacteria on Earth. Other scientists have argued instead that the magnetite in ALH84001 was likely caused by inorganic processes, and that those same processes can be recreated artificially in the laboratory by heating carbonates in a process known as thermal decomposition, forming magnetite identical to that found in the Mars meteorite.
In this new study, the JSC research team reassessed the leading alternative non-biologic hypothesis that heating or shock decomposition produced the magnetites. The authors argue that their new results do not support the heating hypothesis for the formation of the magnetites. They conclude that the biogenic explanation is a more viable hypothesis for the origin of the magnetites.
“The evidence supporting the possibility of past life on Mars has been slowly building up during the past decade,” said McKay, NASA chief scientist for exploration and astrobiology, JSC. “This evidence includes signs of past surface water including remains of rivers, lakes and possibly oceans, signs of current water near or at the surface, water-derived deposits of clay minerals and carbonates in old terrain, and the recent release of methane into the Martian atmosphere, a finding that may have several explanations, including the presence of microbial life, the main source of methane on Earth."
You can get all the juicy details on the NASA site, but the thrust of the finding is clear: the evidence for life on Mars in the past and possibly in the present is strengthening. Now, it should be noted that this does not necessarily mean that life emerged independently on Mars. Material from Mars has ended up on Earth through natural processes and the reverse could have taken place.** So, it may well be that any Martian life we discover may have originated on Earth or, you know, vice versa. Nevertheless, this is exciting stuff and I can't wait to see what's coming next!
* I've mentioned all that previously.
** Granted, the Earth is more massive and therefore possesses a deeper gravity well, making it more difficult for lifeforms to survive the sorts of events that could transport them to Mars in the first place.