Scientists have recovered clumps of petrified nanobacteria from the flanks of an extinct worm. They are believed to be the smallest fossilised lifeforms discovered.
The 540 million-year-old remains are thought to be the first example of fossil microorganisms of the sort responsible for the decomposition of organic matter.
Ironically, the success of such entities in breaking down dead plants and animals is in part responsible for the scarcity of all types of fossil found today.
The discovery was made by Malgorzata Moczydlowska, professor of micro-palaeontology at Uppsala University in Sweden. Her findings were reported to the Palaeontological Association in Copenhagen this week.
Professor Moczydlowska examined a fossil worm, Sabellidites cambriensis , that was extracted from a borehole in Lithuania.
When the remains were magnified 2,500 times with a scanning electron microscope, she found large numbers of tiny filaments densely packed in irregular colonies on the surface of the worm's body tube. Examination and analysis of their chemical signature revealed they were organic and were neither modern contaminants nor mineral deposits.
They appeared flexible and deformed like macaroni, with lengths between two and five microns and between 209nm and 324nm in width. Professor Moczydlowska identified them as nanobacteria.
The microorganisms were preserved in tiny depressions in the side of the worm. Pyrite deposits around them suggested that they had been digesting their host and released hydrogen sulphide as a metabolic by-product.
After the worm died, the nanobacteria started eating into it in oxygen-free water at the bottom of a marine basin. Within days they were covered by sediment, perhaps stirred up by a storm. Nanobacteria activity ceased and they were rapidly fossilised.
The discovery may help astrobiologists to identify chemical signatures that could lead to the identification of fossilised extraterrestrial life.