The existence of a terrestrial Precambrian (more than 542 Myr ago) biota has been largely inferred from indirect chemical and geological evidence associated with palaeosols, the weathering of clay minerals and microbially induced sedimentary structures in siliciclastic sediments. Direct evidence of fossils within rocks of non-marine origin in the Precambrian is exceedingly rare. The most widely cited example comprises a single report of morphologically simple mineralized tubes and spheres interpreted as cyanobacteria, obtained from 1,200-Myr-old palaeokarst in Arizona. Organic-walled microfossils were first described from the non-marine Torridonian (1.2-1.0 Gyr ago) sequence of northwest Scotland in 1907. Subsequent studies found few distinctive taxa-a century later, the Torridonian microflora is still being characterized as primarily nondescript "leiospheres". We have comprehensively sampled grey shales and phosphatic nodules throughout the Torridonian sequence. Here we report the recovery of large populations of diverse organic-walled microfossils extracted by acid maceration, complemented by studies using thin sections of phosphatic nodules that yield exceptionally detailed three-dimensional preservation. These assemblages contain multicellular structures, complex-walled cysts, asymmetric organic structures, and dorsiventral, compressed organic thalli, some approaching one millimetre in diameter. They offer direct evidence of eukaryotes living in freshwater aquatic and subaerially exposed habitats during the Proterozoic era. The apparent dominance of eukaryotes in non-marine settings by 1 Gyr ago indicates that eukaryotic evolution on land may have commenced far earlier than previously thought.

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This paper outlines the suite of advanced multi-scalar techniques currently available in the toolkit of the modern Proterozoic palaeobiologist. These include non-intrusive and nondestructive optical, laser and X-ray techniques, plus more destructive ion beam and electron beam methods. Together, these provide morphological, mineralogical and biochemical data at flexible spatial scales from that of an individual atom to the largest Proterozoic microfossils. An overview is given of each technique and a case study from the exceptionally well-preserved Torridonian biota of NW Scotland is presented. This microfossil assemblage was first recognized over a century ago, but its great diversity and evolutionary importance has only recently come to light, due in no small part to the research efforts of Martin Brasier.

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. Evidence for terrestrial interpretations from each Formation of the Torridonian Supergroup is first considered. The range of sedimentary structures, and the boron content of illite lead to an overall conclusion that, on present evidence, the Torridonian Supergroup was likely entirely non-marine. Evidence for terrestrial life in these rocks comes from microbially induced sedimentary structures (MISS) 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. The Precambrian is no longer the fossil-barren 'Lost World' that intrigued Charles Darwin. Over the last several decades there have been significant advances in understanding of the evolving early marine biosphere (see for example Brasier et al., 2015). Questions remain, however, over the extent to which life had colonized terrestrial environments during the Proterozoic and early Palaeozoic. In