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Precambrian mudrock from source-to-sink: an Earth analogue to identify pre-multicellular life habitable environments that have high biosignature preservation potential
Lead Supervisor: Neil S. Davies, Department of Earth Sciences
Co-supervisor: William J. McMahon, Department of Earth Sciences

Brief summary
Discovering signs of ancient extra-terrestrial life requires not only habitable paleoenvironments, but a subset of those where preservation of biosignatures was likely. Earth’s mudrock archive is a highly productive repository of fossil material, but it underwent step-changes in composition and mineralogy due to the evolution of bioturbation and land plants. The mudrock record predating these will be investigated to identify where different mud types (variable clay composition and physical attributes) were deposited in ‘source-to-sink' linked environments (i.e., from mountains, through rivers, to sea) when there was only a nascent microbial biosphere, potentially analogous to other planets.

Importance of the area of research concerned
Mudrocks could be key in the search for ancient extra-terrestrial life. Often deposited in habitable environments, their lithification is also suited for preserving biosignatures. Our understanding of mudrock is biased towards modern Earth, where biosphere influences are profound. To capitalize the potential of extra-terrestrial mudrock we need to understand Earth’s mudrocks from before the widespread establishment of life. The 1.5-billion-year-old Belt Supergroup is a natural laboratory recording mudrock-forming processes prior to multicellular life. Modern sedimentological investigation will 1) characterise environments that were a cradle for nascent microbial life, and 2) identify how mud transport and deposition operated before multicellular life, permitting comparisons to see how planetary environments can be shaped by life. Samples will be subjected to analyses of their clay minerals, utilizing cutting-edge electron imaging. These efforts will show which environments saw the deposition of mudrocks with high clay contents, identifying analogous astrobiological targets for recovering biosignatures.

What will the student do?
The Belt Supergroup of the NW USA is a widespread rock unit recording deposition in linked environments from mountain sources, through river conduits, to sinks in ancient lakes and seas.  The unit dates from before the advent of multicellular life and is overdue a sedimentological field investigation identifying different architectural styles of mudrock across these environments, framed as an analogue for similar environments on other planets. Fieldwork will allow the student to undertake this and collect contextualized samples. The student will conduct a state-of-the-art petrographic analysis of the recovered samples to determine which environments host the most desirable clay assemblages for organic matter preservation. New techniques in automated scanning electron microscope (SEM) energy dispersive spectroscopy (EDS) mineral mapping will assess how the clay mineral content varies between environments and which were most likely to retain organic matter through clay-organic bonding.

Han, S., Lӧhr, S.C., Abbott, A.N., Baldermann, A., Farkaš, J., McMahon, W., Milliken, K.L., Rafiei, M., Wheeler, C. and Owen, M., 2022. Earth system science applications of next-generation SEM-EDS automated mineral mapping. Frontiers in Earth Science, 10, p.956912.

McMahon, W.J. and Davies, N.S., 2018. Evolution of alluvial mudrock forced by early land plants. Science, 359(6379), pp.1022-1024.
Schieber, J., 1998. Possible indicators of microbial mat deposits in shales and sandstones: examples from the Mid-Proterozoic Belt Supergroup, Montana, USA. Sedimentary Geology, 120(1-4), pp.105-124.

Requirements as to the educational background of candidates that would be suitable for the project
The project is suited to a student with a background in Earth Sciences, Geology or a related subject.

You can find out about applying for this project on the Leverhulme Centre for Life in the Universe widening participation PhD Studentships page.