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Published November 29, 2016 | Supplemental Material
Journal Article Open

Constraints on ocean carbonate chemistry and p_(CO_2) in the Archaean and Palaeoproterozoic

Abstract

One of the great problems in the history of Earth's climate is how to reconcile evidence for liquid water and habitable climates on early Earth with the Faint Young Sun predicted from stellar evolution models. Possible solutions include a wide range of atmospheric and oceanic chemistries, with large uncertainties in boundary conditions for the evolution and diversification of life and the role of the global carbon cycle in maintaining habitable climates. Increased atmospheric CO_2 is a common component of many solutions, but its connection to the carbon chemistry of the ocean remains unknown. Here we present calcium isotope data spanning the period from 2.7 to 1.9 billion years ago from evaporitic sedimentary carbonates that can test this relationship. These data, from the Tumbiana Formation, the Campbellrand Platform and the Pethei Group, exhibit limited variability. Such limited variability occurs in marine environments with a high ratio of calcium to carbonate alkalinity. We are therefore able to rule out soda ocean conditions during this period of Earth history. We further interpret this and existing data to provide empirical constraints for carbonate chemistry of the ancient oceans and for the role of CO_2 in compensating for the Faint Young Sun.

Additional Information

© 2016 Macmillan Publishers Limited. Received 7 June 2016; accepted 25 October 2016; published online 28 November 2016. This work was supported by a grant from the Simons Foundation (SCOL 339006 to C.L.B.). S. A. Maclennan and A. M. Campion aided J.J.K. in collecting Tumbiana samples. D. P. Santiago Ramos and E. A. Lundstrom contributed to laboratory analyses. Author Contributions: C.L.B. conceived of the study; L.R.K., W.W.F., G.P. and J.J.K. conducted field work and collected samples; C.L.B. and J.A.H. obtained and analysed the data. Data availability: The authors declare that the data supporting the findings of this study are available within the article and its Supplementary Information files. The authors declare no competing financial interests.

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