The microfossils that were found in the sample ALH84001 are smaller than any known form of life on Earth.
It is possible that there has been contamination of PAH's form Earth since the meteorite has been sitting in Antarctica for 13000 years, infiltration of water may have also occured after the time of impact.
During the Viking missions, none of the compounds found in ALH84001 were picked up.
The oxidized minerals and other compounds can be explained by non-biological processes.
The wisker-like magnitite crystals are associated with high-temperature activity which can not support waterbased life. There are also spiral defects within the magnetite crystals which have never been seen produced by organic processes.
The carbonate deposition has a more recent age, indicating that the mineral was derived from a hot vapor not liquid water. this also weakens the theory of a biological origin.
Professor Dr. Denis Shaw, from McMaster University, studies meteorites for traces of the rare element Boron and who had had the sample ALH84001 in his posession for nearly 10 years. He says that he has never seen any signs of life on or in this rock.
The NASA team of reasearchers did not include a micropalentologist.