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Life on other Planets
by Thomas Gold
May 1997
Highly oxidized iron is abundant on Mars, and very small-grained magnetite can then be expected to be one of the accumulated residues of microbial processes; so can iron sulfide and methane-derived carbonates. Polycyclic aromatic hydrocarbons are the large molecules that might remain in a rock that originally contained crude oil but then was exposed for millions of years to the high vacuum of space. All these substances have been found in the discovery meteorite, closely packaged to each other, and this by itself would make a strong case for the microbial interpretation. In addition, there are small objects seen under scanning electron microscopy that may well be fossils of microbes. While the last item by itself would not be conclusive evidence, the combination of this together with oil and the three residue products make a strong case for the microbial explanation. It is true that each step can occur without biological intervention, but the chance of finding by chance the evidence for all three solids in a small volume, together with hydrocarbons, seems to be very low. Many terrestrial oil and gas wells show just such an association (but an association with helium also, which the meteorite could not have transported through space).

The Deep, Hot Biosphere
by Thomas Gold
foreword by Freeman Dyson