SETI bioastro: Martian nanofossils - just lumps of protein?

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http://www.nature.com/nsu/030804/030804-4.html

Nanofossils may be digested organic matter
Alleged remains of tiny ancient bacteria could just be balls of protein.

6 August 2003

Tiny geological features thought by some to be the fossil remains of primitive bacteria are probably nothing more than fossilized lumps of lifeless protein, say two US scientists.
The structures, dubbed nanobacteria, are typically 50-200 millionths of a millimetre across. They have been found in some sedimentary rocks, and even in the martian meteorite ALH84001, leading to claims of evidence for life on Mars. Debate has raged for eight years over whether or not they are the fossilized remains of single-celled organisms ten times smaller than today's.
Now Jürgen Schieber, of Indiana University in Bloomington, and Howard Arnott, of the University of Texas at Arlington, report that spherical balls of protein about 40-120 nanometres across are produced when organic material decays in an environment like that in which sedimentary rocks form1.
That would certainly fit the conclusions of a panel of scientists convened in 1998 by the US National Academy of Sciences to study the nanobacteria controversy. The committee decided that organisms smaller than about 200 nanometres in diameter would not be viable. That did not end the discussion, however. Some researchers claim to have grown nanobacteria in the laboratory.
Schieber and Arnott dipped pieces of bean, squid and beef into the muck scooped from a pond bed, coating them in a range of natural bacteria, and then buried the samples under clay in a water tank. Over the next fortnight the researchers regularly studied samples under the microscope. The tissues, they found, became covered in spherical blobs of organic matter.
The duo reckon that the balls form when enzymes snip stretched protein fibres of muscle tissue or plant cell wall, say, causing them to contract. Such nanoballs, they suggest, could become mineralized before being degraded completely. Fossilization, they point out, can begin just a few weeks after the onset of decay.
This same process could have occurred within a mass of single-celled organisms on the early Earth, resulting in the apparent fossil forms, Schieber and Arnott suggest. "Most, if not all alleged nanobacterial structures in sedimentary rocks are not evidence for minute life forms," they conclude. The origin of similar structures in meteorite ALH84001 will no doubt remain controversial.

References
Schieber, J. & Arnott, H. J. Nannobacteria as a by-product of enzyme-driven tissue decay. Geology, 31, 717 - 720, (2003).|Article|

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