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Final Report Summary - REPOM (Remarkable Preservation of Precambrian Organic Material)

Introduction and aims: Determining what is and what is not life in Earth’s oldest rocks, and identifying what type of life was present in these environments are fundamental scientific problems. Resolving these questions is vital in order to understand the origin of life on Earth, the role biology played in shaping early Earth environments, the nature and timing of evolutionary transitions, and to evaluate potential extra-terrestrial life. The timing and nature of the earliest life on Earth can only readily be addressed using fossil data, but these data have often been the subject of controversy since they are difficult to interpret and there are few established criteria on which to interpret them.

The main objectives of this project can be summarised as: 1) provide new and more robust data to help determine the authenticity of putative Precambrian life; and 2) determine the type and diversity of life present in some key Precambrian fossil assemblages. Specifically, the project aims to address some important outstanding questions in Precambrian palaeobiology, including (i) evidence for the earliest cellular life (using material from the 3.46 billion-year-old (Ga) Apex Chert and the 3.48 Ga Dresser Formation of Western Australia), (ii) evidence for the nature of early diverse microfossil assemblages, plus insights into what causes remarkable fossil preservation at these times (using material from the 1.9 Ga Gunflint Formation of Canada, plus younger analogues), and (iii) evidence for the nature of early terrestrial (lacustrine) biotas (using material from the 1 Ga Torridon Group of Scotland).

Results: During the project a wide range of state of the art analytical techniques have been applied to key Precambrian fossil assemblages, and to material containing putative fossil remains. Of note, controversial material from the 3.46 Ga Apex chert, once thought to provide evidence of Earth’s oldest fossil cells has been analysed using light microscopy, laser Raman micro-spectroscopy, secondary ion mass spectrometry, focused ion beam serial sectioning, transmission electron microscopy and confocal laser scanning microscopy.

Figure 1. High-resolution electron microscopy of filamentous structures in the 3.46 Ga Apex chert, showing that the elemental distributions (especially carbon, shown in yellow) are incompatible with a biological origin, hence the structures have now been re-interpreted as abiotic mineral artefacts.

The combined data have shown that these filamentous microstructures are not microfossils, but are mineral artifacts formed in a hydrothermal system and are not related to biology. These new data not only finally solve a controversy that has been raging for almost 15 years, but the correlative methodology employed provides a new and exciting protocol for interrogating other putative signs of life on the early Earth. These data were published in two high ranking journals, received international print media and radio attention, and led to the invitation to write a popular science article for The Conversation (

New suites of carbonaceous and pyritic textures from elsewhere in the Apex Chert, and from the slightly older 3.48 Ga Dresser Formation have also been investigated using the tools outlined above, plus laser scanning and CT scanning. These macroscopic and microscopic sedimentary structures appear to preserve the interaction of microbes with sediment and may now be used as signatures for ancient life (and potentially life on other planets). A range of potentially biological microtubular structures have also been investigated from both Precambrian (1.9 Ga Gunflint Chert) and more modern rocks. These structures resemble microbial borings but this project has shown them to occur when a mineral crystal is propelled through a rock matrix. They commonly occur in association with organic material and several lines of evidence now suggest that biology plays a role in their formation, although this is not the only viable formation mechanism.

Significant progress has been made in elucidating the nature and styles of preservation of non-marine biotas in the Precambrian with results from this project indicating substantial differences in lake chemistries between lakes of similar ages (~1 Ga Torridon Group) in northwest Scotland, leading to exceptional preservation of organic material in one lake system, but poor preservation in another. The exceptionally preserved microfossils have been further investigated, with new data suggesting that distinct sub-cellular features can be recognised in such fossils. This provides a new and exciting opportunity to recognise key features such as nuclei and other organelles, thus greatly aiding the ability to classify Precambrian organisms and, in turn, enhancing their evolutionary significance.

The project has also led to a greater understanding of the environmental conditions and local chemistry that leads to remarkable preservation of organic material. Of particular note here is my work reporting the first ever fossilised dinosaur brain tissue from an Iguanodontian dinosaur from the Cretaceous of southern England. Preservation of meninges and blood vessels from the outer portion of the brain required a very specific anoxic and nutrient rich micro-environment which provides a useful analogue to conditions required for remarkable preservation of Precambrian microorganisms. This work was highly cited by the media (e.g., BBC, CNN, National Geographic, New Scientist and Science Magazine) and has also lead to my inclusion in the Guinness Book of World Records.

In summary, this project has successfully shown that analysis of remarkably preserved organic material at the micrometre to nanometre scale provides a new and unique suite of data that in turn provides more robust interpretations of the authenticity of putative signs of Precambrian life, and provides new insights into the type of life present in Precambrian fossiliferous deposits.

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