7.9 Terrestrial Environments

Abstract

In contrast to a rather extensive marine sedimentary record of the Palaeoproterozoic, the terrestrial record, preserved as palaeosols (ancient soils; Retallack 2001) and caliches or calcretes (carbonate layers in palaeosols; Wright and Tucker 1991), is sparse. Nevertheless, these deposits are important, because they have the potential to provide the least ambiguous information on climatic and atmospheric compositional change during this critical interval of Earth history. In the best of circumstances, marine sediments record oceanic conditions, which can differ markedly from atmospheric conditions, especially in terms of redox. In the modern world, soil environments themselves poorly reflect those at the surface, especially in terms of CO₂ and O₂ partial pressure, because of respiration by roots and soil microbes. But in the Palaeoproterozoic, with its presumably poorly developed terrestrial biota, soil conditions likely track those of the atmosphere much more closely. (We use “presumably” here, because terrestrial ecosystems may have been extensive (Horodyski and Knauth 1994; Watanabe et al. 2000), and the land surface may have been the incubator for early evolutionary innovation, including the origin of cyanobacteria; e.g. Battistuzzi et al. 2009).