Since 1976 the National Science Foundation has funded the Antarctic Search for Meteorites program, which has returned 8,000 specimens of meteorites stranded on the ice along the Transantarctic mountains. Meteorites falling on Antarctica are hitting a cold desert. Marooned in ice, they progress outwards as the ice sheet flows to the margins of the continent. Where the icesheet has to cross mountains, old ice is pushed to the surface and severely ablated by katabatic winds. The meteorites come out of the deep freeze and can be found rather easily as dark rocks resting on a white background, in concentrations up to one per square meter.

   Hot Paper #1 centers on meteorite ALH84001, found in the Allan Hills region of Antarctica 14 years ago. Its possible martian origin remained unrecognized until 1993. It is one of only 12 meteorites identified so far that match the unique martian chemistry measured by the Viking landers in 1976, and it is by far the oldest. Mass spectrometry experiments by Viking failed to find organics at the martian surface. ALH84001 is a very primitive magnesium- and iron-rich rock that formed in a magma chamber deep beneath a martian volcano. This friable rock has many crushed and fractured zones, resulting from many generations of hard pounding from impacts while sitting on the surface of Mars. What excites the planetary mineralogists is the presence of secondary minerals with the orthopyroxene matrix. An impact of a comet or asteroid with Mars 16 million years ago blasted ALH84001 into a solar orbit than finally crashed it on Antarctica.

   In paper #1 the NASA team, based at the Johnson Space Center, Houston, and Stanford University, California, set out evidence which they say, on balance, suggests primitive life once carved out an existence inside the meteorite. Their analysis is based on interpretation of high-resolution scanning and transmission electron microscopy (SEM, TEM) of the surfaces of small samples from ALH84001. The objective was to look for biomarkers in the interstices of the rock.

   The first conclusion reached by David McKay and the Johnson-Stanford team is that ALH84001 was penetrated along its cracks by water rich in CO₂, and this led to secondary mineral formation of carbonates. The recent impressive evidence from Mars Pathfinder of water on ancient Mars must reinforce this conclusion. The next step in the argument establishes a formation age for carbonate globules which is less than the age of the igneous rock. Step 3 is Show and Tell: SEM and TEM images are morphologically similar to nanofossils, tubular and ovoid structures strikingly similar to microscopic fossils of the smallest bacteria found on Earth.

   Stage 4 of the case is that unusual compounds of magnetite and iron sulfide particles are typical of those that could have resulted from oxidation and reduction reactions known to be important in terrestrial organisms. These compounds were found in locations next to the fossil structures. Tiny grains of magnetite are almost identical to magnetic relics left by some earthly bacteria.

   The final piece of evidence is the presence of polycyclic aromatic hydrocarbons (PAHs). On Earth these are associated with ancient sedimentary rocks (coals, petroleum beds), and so the argument is that on the microscopic level their presence in ALH84001 is the result of a fossilization process.

   The evidence in #1 has its critics. Nature on December 4, 1997 offered a rebuttal led by Ralph Harvey (Case Western Reserve University) which states that the nanofossils are nothing more than the fractured surfaces of pyroxene and carbonate crystals. His team used essentially the same techniques but reach the different conclusion that the nanofossil structures are artifacts from the metal coatings applied to samples prior to TEM imaging. Of itself this does not kill the life on Mars debate: it breathes new life into it!