Chapter 3 Terrestrial Ecosystems in the Precambrian

Three lines of evidence for ancient life on land are paleosols, microfossils, and MISS (microbially induced sedimentary structures). The three appear in the rock record as old as 3.5–2.7 Ga (Hallbauer and van Warmelo 1974; Rye and Holland 2000; Wacey et al. 2008; Johnson et al. 2010; Noffke et al. 2013). The primitive terrestrial biosphere is plausibly as old as the oldest marine biosphere (Schopf 1983; Schopf and Klein 1992), with both aquatic and terrestrial realms teeming with life 3.5 Ga ago. This result is unsurprising considering the modern ecological capabilities of microbes, which are comparable with fossil analogs and have profound effects in sediments and soils (Belnap and Lange 2001; Navarro-González et al. 2003; Beraldi-Campesi and Garcia-Pichel 2011; Retallack 2012). Functional aquatic and terrestrial ecosystems may be even older than 3.5 Ga, but undisputable biosignatures before that time are ambiguous (Nutman et al. 2010; Papineau et al. 2010), and the timing when life first populated the Earth is still unresolved. Direct evidence for ancient terrestrial communities comes from the fossil record, and the several limitations of such should be noted. First, it has many temporal gaps, which makes it difficult to appreciate the continuous history of life on Earth (Sadler 1981). Second, not all the rocks have been studied in detail, especially biosignatures preserved in it, so that recent and future discoveries may yield more tangible information about the history of the biosphere (Dutkiewicz et al. 2006). Third, microbial biological diversity of the Precambrian fossil record is