[meteorite-list] Nanofossils In ALH84001 May Be Digested Organic Matter

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:29 2004
Message-ID: <200308061612.JAA09342_at_zagami.jpl.nasa.gov>

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.

Philip Ball
Nature Science Update
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 Jurgen 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 form[1].

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

    1. Schieber, J. & Arnott, H. J. Nannobacteria as a by-product of
       enzyme-driven tissue decay. Geology, 31, 717 - 720,
       (2003).|Article|
Received on Wed 06 Aug 2003 12:12:59 PM PDT