Portion of ancient Australian chert microstructures definitively pseudo-fossils

February 16, 2016
Different types of imaging show the microstructure that was originally designated as the fossil Eoleptonema apex. Credit: Dina Bower and Andrew Steele

A team of scientists including Carnegie's Dina Bower and Andrew Steele weigh in on whether microstructures found in 3.46 billion-year-old samples of a silica-rich rock called chert found in Western Australia are the planet's oldest fossils. The purported fossils have been a heated scientific controversy for many years. The team asserts that at least a portion of the microstructures are actually pseudo-fossils. Their findings are published in Astrobiology.

More than two decades ago, microscopic filamentary structures, less than two dozen micrometers in length, found in Australia's Apex chert formation were declared to be fossils of photosynthetic bacteria from the Archean eon. These alleged microfossils were obviously of great interest to scientists interested in the origins of life on Earth as well as those trying to determine the best way to look for life on other planets.

But since then, subsequent research involving Owen Green at Oxford University (who is also a co-author on this study) has called these claims into question, putting forward the idea that the structures are fossil-like mineral formations, but not actually the remains of life. Debate about the authenticity of the Apex chert microfossils has raged over the last several years.

The research team—which also included Marc Fries of the NASA Johnson Space Center and John Lindsay (now deceased) of the Lunar and Planetary Science Institute—analyzed the orientation of the quartz crystals (quartz is a form of silica, which makes up chert) surrounding the alleged microfossils in order to determine whether the crystals and microstructures were both formed as part of the same geological processes.

"Based on our findings, we think that the Apex fossil that was designated as Eoleptonema in the originally described samples that we re-studied here was actually formed when a series of quartz grains cracked and was filled in with carbon-rich material to create a sheet-shaped structure within the larger crystal," Steele explains.

The source of the carbon could have been biological, or abiotic, but this structure itself is not a fossil, the team asserts.

"Studies have shown that 60 percent of the originally described alleged microfossils were found in material that is younger than its host rock, E. apex being one such example. This study further develops a new technique in order to study the indigeneity of the microfossils in the rock and shows without a doubt that this particular example is a pseudo-fossil. The other in the primary rock (i.e. the oldest part of the ) should now be analyzed critically in order to prove that similar processes have not been responsible for the formation of those features," said Bower.

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4 comments

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AGreatWhopper
3 / 5 (2) Feb 16, 2016
putting forward the idea that the structures are fossil-like mineral formations, but not actually the remains of life.


Yeah, that's the rub. ALL fossils are mineral formations. The earliest living things were often simple repetitions of stable geometric structures, so, there would have to be a point where you can't tell one from the other, no?

These fossils remind me of the cranks' theories on here. They fantasize about the establishment dropping all consensus and slavishly hanging on every word of their pet theories but never realize that if such a thing DID happen it would be meaningless. The meaning comes from the context. In the same way there will have to be more robust biochemical models of early life that these fossils rule in/rule out before they have any meaning.
torbjorn_b_g_larsson
5 / 5 (1) Feb 17, 2016
Poor Schopf, earlier his whole Apex assemblage came into suspicion for pattern recognition with lack of context (e.g. the recently deceased Brasier et al), then his kerogen examples are more or less all showed to be later leaching into inorganic formations. Background here, including images with the present pseudofossil: http://www.astrob...n-rocks/

[tbctd]
torbjorn_b_g_larsson
5 / 5 (1) Feb 17, 2016
[ctd]

"More than two decades ago, microscopic filamentary structures, less than two dozen micrometers in length, found in Australia's Apex chert formation were declared to be fossils of photosynthetic bacteria from the Archean eon."

Schopf himself clarifies: "... he calls the argument over cyanobacteria a "red herring. I have referred to these specimens as 'cyanobacterium-like,' 'possible cyanobacteria,' and even 'probable cyanobacteria,' but I have never, ever claimed that they were cyanobacteria per se. ... I said they were prokaryotes."
torbjorn_b_g_larsson
5 / 5 (1) Feb 17, 2016
@AGW: That clays or solid crystals, with their repetitive or at least stable chemical and/or geometric structures, was part of or helped early life is one theory among others.

More generally, early life emerged out of geology and wasn't capturing many element cycles (the carbon cycle, say) or energy (photosynthesis, say) as much. So there was, as you say, a gradualism that makes for little in the way of very early fossils.

Pseudofossils is another problem, here the context - that you rightly identify as necessary - is lacking (and hence the confusion between them and fossils). The Apex Chert pseudofossils goes back to a time where the importance of context wasn't understood. It is much harder to ascertain and publish on microfossils today, you often see proposals for fossil candidates rather than controversial claims with insufficient support.

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