Mars, Page 15: [Previous Page] [Next Page] [Syllabus] Textbook pages 142 - 159

Indications of Past Life on Mars, Part Deux

3) Evidence for Fossil Bacteria
Perhaps the most striking evidence for past life on Mars is the following pictures.

Elliptical, ropelike, and tubular structures in fractures in the carbonate mineral globules were found and interpreted as structures of possible fossil bacteria. These structures are 20 to 100 billionths of a meter across (or nanometer, abbreviated "nm"), and only seen with an electron microscope. Similar terrestrial "nanobacteria" have been found, but it is not universally agreed that they are biological in origin either.

The original scientists tried to show that: (a) the bacteria shapes are actually the sizes and shapes of known living organisms, (b) the bacteria shapes are really part of the rock and were not produced accidentally while they prepared the sample for study, and (c) the bacteria shapes are not Earth bacteria that somehow wiggled into ALH 84001 while it was in Antarctica.

However, inorganic processes can sometimes produce elliptical and tubular structures and ancient bacteria on Earth were hundreds of times larger than the structures in ALH 84001. Many scientists warn that finding bacteria-shaped structures isn't enough. Many scientists want evidence of cell walls, reproduction, growth and colonies of cells, before believing this evidence. A fairly recent professional review of the evidence is given here.