Earth’s Oldest Fossils
of mica, plus the redistribution of barium, iron, and carbon during repeated episodes of fluid movement within a hydrothermal system.
Acknowledgements We acknowledge the facilities and
scientifi c and technical assistance of the Australian Microscopy & Microanalysis Research Facilities at: Centre for Microscopy Characterisation and Analysis, T e University of Western Australia; Electron Microscopy Unit, T e University of New South Wales. T ese facilities are funded by the Universities, State, and Commonwealth Governments. David Wacey acknowl- edges funding from the European Commission and the Australian Research Council. Anthony Burgess from FEI is thanked for the preparation of one of the TEM wafers.
References [1] JW Schopf and BM Packer , Science 237 ( 1987 ) 70 – 73 .
[2] JW Schopf , Science 260 ( 1993 ) 640 – 46 .
Figure 5 : 3D reconstruction of Apex fi laments. (a) Transmitted light photomicrograph of a fi lament. (b) 3D visual- ization of carbon from FIB-SEM images through the fi lament, shown in the same orientation as (a). (c) 3D model rotated to show small branch extending down below the main body of the fi lament, not seen in (a–b). (d) Transmitted light photomicrograph of a second fi lament. (e) 3D visualization of carbon from FIB-SEM images through the fi lament, shown in the same orientation as (d). Note patches of carbon outside the main body of the fi lament. (f) 3D model rotated and enlarged to highlight the linear nature of much of the carbon coating the phyllosilicate grains.
action of slit-like pores between plate-like grains. Today vermiculite is used extensively for cleaning up oil spills [ 20 ]. T is work has important implications for the evaluation of primitive life on Earth and, by extension, in extraterrestrial settings. Herein, candidate microfossils that appear to pass most currently accepted biogenicity criteria when examined at the micrometer scale have been shown to fail several criteria when examined at the sub-micrometer scale. Hence, future work should focus on the refi nement of biogenicity criteria using bone-fi de microfossils and defi nitive non-biological microfossil-like artifacts examined at the sub-micrometer scale.
Conclusion
Analysis of new material from the Apex chert “microfossil locality” using high spatial resolution electron microscopy has demonstrated that filamentous microstruc- tures, previously thought to be Earth’s oldest microfossils, are in fact mineral artifacts comprising stacks of phyllosil- icate grains onto which later carbon adsorbed. Rather than being fossilised microorganisms, we interpret the filaments as resulting from the alteration and exfoliation of flakes
16
[3] JW Schopf , “Paleobiology of the Archean” in T e Proterozoic Biosphere: a multidisciplinary study , eds. JW Schopf C Klein, Cambridge University Press , Cambridge, UK , 1992 , 25 – 39 .
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[13] JW Schopf and AB Kudryavtsev , Gond Res 22 ( 2012 ) 761 – 71 .
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