Testing enhanced surface weathering hypotheses for Snowball Earth

The Cryogenian Period, which began around 720 million years ago, was marked by prolonged low-latitude glaciations known as ‘Snowball Earth’. The prevailing hypothesis is that these global cooling events were driven by enhanced weathering of continental fragments in the tropics during the breakup of the Rodinia supercontinent. To test this idea, we applied a Bayesian network analysis (cf. Gernon et al., 2021) to examine the statistical relationship between seawater chemistry (⁸⁷Sr/⁸⁶Sr) and the fraction of continental land in the tropics, as inferred from recently available plate tectonic reconstructions. Our results reveal a weak overall correlation between these variables, even when accounting for multi-million-year time lags and the effects of auto-correlation in the time series. This finding suggests that the Earth's weathering response to global tectonic reorganisation is more complex than previously assumed. We conclude that while enhanced chemical weathering may have driven Snowball Earth, it likely arose from processes other than the first-order distribution of continents in the tropics, although a secondary influence cannot be excluded. Finally, we explore alternative plate tectonic mechanisms that yield unexpectedly long time lags between continental breakup and changes in ocean chemistry and climate, which may help reconcile disparate observations from the geologic record.

Reference

Gernon, T.M., Hincks, T.K., Merdith, A., Rohling, E.J., Palmer, M.R., Foster, G.L., Bataille, C.P. and Muller, D. Global chemical weathering dominated by continental arcs since the mid-Palaeozoic. Nature Geoscience 14, 690–696, doi: 10.1038/s41561-021-00806-0 (2021).