Prehistoric animals likely did not attain significantly greater depths; dinosaur burrows, for example, were long unrecorded, and the single example known ( Varricchio et al., 2007) is not much more than 20 cm across and

lies less than a metre below the palaeo-land surface. Plant roots can penetrate depths an order of magnitude greater, especially in arid regions: up to 68 m for Boscia truncata in the Kalahari desert ( Jennings, 1974). They can be preserved as rootlet traces, generally through diagenetic mineral precipitation or remnant carbon traces. Roots, though, typically infiltrate between sediment grains, limiting the amount of sediment displacement and hence disruption to the rock fabric. selleck kinase inhibitor At a microscopic level, too, there is a ‘deep biosphere’ composed of sparse, very slowly metabolizing microbial communities that can exist in pore spaces and rock fractures to depths of 1–2 km (e.g. Parkes et al., 1994). These may mediate diagenetic reactions where concentrations

of nutrients allow larger populations (such as the ‘souring’ of oil reservoirs) but otherwise leave little trace in the rock fabric. Very rarely, these communities have been found to be accompanied by very deep-living nematode worms (Borgonie GDC-0973 in vitro et al., 2011), but these seem not to affect the rock fabric, and we know of no reports of their fossil remains or any traces made by them. The extensive, large-scale disruption of underground rock fabrics, to depths of >5 km, by a single biological species, thus represents a major geological innovation (cf. Williams et al., 2014). It has no analogue in the Earth’s 4.6 billion year history, and possesses some sharply distinctive features: for instance, the structures produced reflect a wide variety of human behaviour effected through tools or more typically mechanized excavation, rather than through bodily activity. Hence, the term ‘anthroturbation’ (Price et al., 2011; see also Schaetzl

and Anderson, 2005 for use in soil terminology) is fully justified, and we use this in subsequent description below. This is extensive, HSP90 and distantly analogous to surface traces left by non-human organisms. It includes surface excavations (including quarries) and constructions, and alterations to surface sedimentation and erosion patterns, in both urban and agricultural settings. Its nature and scale on land has been documented (e.g. Hooke, 2000, Hooke et al., 2012, Wilkinson, 2005, Price et al., 2011 and Ford et al., 2014) and it extends into the marine realm via deep-sea trawling (e.g. Puig et al., 2012) and other submarine constructions. Here we simply note its common presence (Hooke et al.