|Filamentous structures from the Apex Chert|
The fossils were quite complex for their proposed place in the history of life. Additionally their colouration was unusual - amber rather than black, typical of microfossils. This led Martin Brasier from the University of Oxford to posit that they were inorganic mineral structures. Chemical analysis of the surrounding rock showed that it had formed in a hydrothermal vent system. Therefore the supposed microfossils could have been inorganic minerals covered in a skin of accreted carbon. The organic and inorganic hypotheses have competed against each other for the past 13 years, but now a recent study is set to settle the debate.
Dr David Wacey, working in conjunction with Martin Brasier before his death earlier this year, conducted an elemental analysis of a range of microfossils using transmission electron microscopy. The analysis included specimens from the Apex Chert. The results were used to compile nanoscale maps of the distribution of carbon in the structures. Previously, imaging techniques did not have the sub-micrometre resolution to make this kind of study possible. These new maps, however, were detailed enough to allow the origin of the microstructures to be identified. The deposition of layers of clay within the hydrothermal vent systems resulted in the formation of filamentous structures. Dissolved carbon in the vent fluids then adsorbed onto the edges and in between the clay layers, giving a false chemical signature of an organic origin.
|An elemental map of a filamentous structure from the Apex Chert, |
showing aluminium rich clay layers interspersed with bands of carbon
While it is sad to see these hallowed 'fossils' deposed, the late Martin Brasier had this to say: 'this research should, at long last, provide a closing chapter for the Apex microfossil debate. Such discussions have encouraged us to refine both the questions and techniques needed to search for life remote in time and space, including signals from Mars or beyond. It is hoped that textbooks and websites will now focus upon recent and more robust discoveries of microfossils of a similar age from Western Australia, also examined by us in the same article.' While the oldest known fossils are not 3.46 billion years old, we can be rest assured that lie is still incredibly ancient.