Correlative microscopy: a tool for understanding soil weathering in modern analogues of early terrestrial biospheres

March 24, 2021

Ria Mitchell (1,2,3), Paul Davies (1), Paul Kenrick (2), Tobias Volkenandt (4), Cameron Pleydell-Pearce (1), Richard Johnston (1)

EarthArXiv, March 2021. DOI: 10.31223/X5860Z


Tomography; Microscopy; Correlative microscopy; Plant evolution


Correlative imaging provides a method of investigating complex systems by combining analytical (chemistry) and imaging (tomography) information across dimensions (2D-3D) and scales (centimetres-nanometres). We studied weathering processes in a modern cryptogamic ground cover (CGC) from Iceland, containing early colonizing, and evolutionary ancient, communities of mosses, lichens, fungi, and bacteria. Targeted multi-scale X-ray Microscopy (XRM) of a grain in-situ within a soil core revealed networks of surficial and internal features (tunnels) originating from organic-rich surface holes. Further targeted 2D grain characterisation by optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (SEM-EDS), following an intermediate manual correlative preparation step, revealed Fe-rich nodules within the tunnels. Finally, nanotomographic imaging by focussed ion beam microscopy (FIB-SEM) revealed coccoid and filamentous-like structures within subsurface tunnels, as well as accumulations of Fe and S in grain surface crusts, which may represent a biological rock varnish/glaze. We attribute these features to biological processes. This work highlights the advantages and novelty of the correlative imaging approach, across scales, dimensions, and modes, to investigate biological weathering processes. Further, we demonstrate correlative microscopy as a means of identifying fingerprints of biological communities, which could be used in the geologic rock record and on extra-terrestrial bodies.

How Our Software Was Used

Dragonfly was used for the visualisation and quantification of tunnel thickness, volume and theta. It was also used to visualize and render 3D volumes.

Author Affiliation

(1) Advanced Imaging of Materials (AIM) Facility, College of Engineering, Bay Campus, Swansea University, Swansea, SA1 8EN, UK
(2) Earth Sciences Department, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
(3) Sheffield Tomography Centre (STC), The University of Sheffield, North Campus, Broad Lane, Sheffield, S3 7HQ, UK
(4) Carl Zeiss Microscopy GmbH, Carl-Zeiss-Straße 22, 73447 Oberkochen, Germany