Life on Mars, or Miniscule Balls of Digested Matter?
The famous Martian meteorite, ALH84001, may finally be allowed to rest in peace. This particular rock possessed geological features that some scientists considered as fossil remains of some primitive bacteria. The structures look like a chain of miniature balls, typically 50-200 millionths of a millimeter across. Their tiny size earned them the name nanobacteria. But a recent study has determined that they may be nothing more than the product of decayed organic material.
Jürgen Schieber, of Indiana University in Bloomington, and Howard Arnott of the University of Texas at Arlington, have reported that “spherical balls of protein about 40-120 nanometers across are produced when organic material decays in an environment like that in which sedimentary rocks form” (Ball, 2003). Their paper, which appeared in the August issue of Geology, noted that they were able to produce “abundant proteinaceous spheroids in the size range of nanobacteria” (Schieber and Arnott, 2003, 31:717).
Previously, we have addressed the various assertions regarding life forms having been found in this meteorite (see: “Life on Mars—The Rest of the Story” and “Mars Rock Update”). One interesting point, discussed by science writer Philip Ball, is that since it was first claimed that these spherical balls might be nanobacteria, “some researchers have claimed to have grown nanobacteria in the laboratory.”
Scheiber and Arnott believe the balls form when enzymes snip stretched protein fibers of muscle tissue or plant cell wall, causing them to contract. They suggest that these nanoballs could become mineralized before being completely degraded, and pointed out that fossilization can begin just a few weeks after the onset of decay. Obviously, this means that the material easily could have originated once the rock was here on the Earth. The authors concluded: “Most, if not all alleged nanobacterial structures in sedimentary rocks are not evidence for minute life forms” (Ball, 2003, emp. added). Send in the Mars rover, boys; this rock is nothing more than a rock.
Ball, Philip (2003), “Nanofossils May be Digested Organic Matter,” Nature ScienceUpdate, [On-line], URL: http://www.nature.com/nsu/030804/030804-4.html.
Schieber, Jürgen and Howard J. Arnott (2003), “Nanobacteria as a By-product of Enzyme-driven Tissue Decay,” Geology, 31:717-720.