The biologic experiments on Mars by Viking Landers and presumptive fossils on the Martian meteorite ALH84001

Conflicting evidences were generated by the Viking Labeled Release (LR) and the Viking Gas Chromatograph Mass Spectrometer (GCMS) experiments conducted on Mars in 1976. While the former gave data satisfying all the pre-mission criteria for the presence of life in a sample of surface material, the latter didn't find any organic compounds. The dilemma was solved by opting for chemistry (presence of peroxides) and not biology. More recently, data obtained on the Martian meteorite ALH84001 have been able to suggest lines of evidence of remains of early life on Mars, in particular with the presence of nannobacteria. According these latter data we may solve the apparent conflict between LR and GCMS experiments. If the microorganism present on the present Mars are nannobacteria, GCMS sensitivity should be unable to detect one million of nannobacteria per g of Martian soil, a quantity sufficient to produce positive results with the LR experiment.