Evaluating evidence from the Torridonian Supergroup (Scotland, UK) for eukaryotic life on land in the Proterozoic

The Stoer, Sleat and Torridon groups lie unconformably on Palaeoproterozoic Lewisian metamorphic rocks. They contain organic carbon microfossils claimed to be non-marine and to include eukaryotes. We consider the evidence for terrestrial interpretations from each formation of the Torridonian Supergroup. The range of sedimentary structures and the boron content of illite led us to the overall conclusion that, based on the currently available evidence, the Torridonian Supergroup was probably entirely non-marine. Evidence for terrestrial life in these rocks comes from microbially induced sedimentary structures, including wrinkle structures with reticulate and elephant skin fabrics. Organic remains and microscopic carbonaceous compressions mostly reported from phosphates in the grey shales of the Stoer, Aultbea and Applecross formations are dominated by sphaeromorph acritarchs. The Diabaig phosphatic lagerstätte includes three-dimensional preservation of eukaryotic and prokaryotic organisms, providing remarkable insights into non-marine life around 1 billion years ago.