LAUSR

Uniformitarianism is a traditional approach used in many areas of geoscience that assumes the geologic processes observed today operated similarly throughout all of Earth history (Hutton, 1788; Windley, 1993), with such an ideology commonly encapsulated by the maxim “the present is the key to the past”. This concept is closely associatedwith the philosophical principle of Occam’s razor, as discussed by Gould (1987) in his critique of its usage in the natural sciences: “we should try to explain the past by causes now in operation without inventing extra, fancy, or unknown causes, however plausible in logic, if available processes suffice”. Nonetheless, although the spatio-temporal constancy of many natural phenomena (e.g. the rate of decay of radiogenic nuclides) appears to promote direct comparison of the modern-day Earth with that of the past, the rock record preserves a wide range of petrological, structural, geochemical, and isotopic evidence for significant changes in earth-system processes and products over geological time. While some of these physio-chemical changes are thought to have occurred gradually, such as secular cooling of the Earth’s mantle (Herzberg et al., 2010), others likely took place over much shorter timescales, such as a rapid rise in the partial pressure of atmospheric O2 at ca. 2.3 Ga (the Great Oxidation Event: Bekker et al., 2004). Such changes in ambient conditions may have significant effects on the geological products that are preserved in the rock record, which has implications for interpretation of past tectonic regimes. How and why these processes have changed over time is important as they affect the mechanisms of growth and reworking of the continental crust (Hawkesworth et al., 2010), contribute to long-term global climate change (Sleep, 2010), and control the location and timing of formation of mineral endowments necessary to support human ambition in the future (Goldfarb et al., 2010). Furthermore, understanding how plate tectonics developed on Earth allows us to gain greater insight into the evolution of other planetary bodies in our solar system and beyond (e.g. Noack and Breuer, 2014; Wade et al., 2017).