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Nano Bacteria Fossils May Be Digested Organic Matter
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
Now Jrgen 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
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
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.