Evidence for sodium-rich alkaline water in the Tagish Lake parent body and implications for amino acid synthesis and racemization

1,2Lee F. White,1,2Kimberly T. Tait,3Brian Langelier,4Elizabeth A. Lymer,1,2Ana Černok,1,2 Tanya V. Kizovski,5Chi Ma,6Oliver Tschauner,1Richard I. Nicklin
Proceedings of the National Academy of Sciences of the United States of America (in Press) Link to Article [DOI: https://doi.org/10.1073/pnas.2003276117]
1Department of Natural History, Royal Ontario Museum, Toronto, ON M5S 2C6, Canada;
2Department of Earth Sciences, University of Toronto, Toronto, ON M5S 3B1, Canada;
3Canadian Centre for Electron Microscopy, McMaster University, Hamilton, ON L8S 4M1, Canada;
4Lassonde School of Engineering, York University, Toronto, ON M3J 1P3, Canada;
5Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125;
6Department of Geoscience, University of Nevada, Las Vegas, NV 89154

Understanding the timing and mechanisms of amino acid synthesis and racemization on asteroidal parent bodies is key to demonstrating how amino acids evolved to be mostly left-handed in living organisms on Earth. It has been postulated that racemization can occur rapidly dependent on several factors, including the pH of the aqueous solution. Here, we conduct nanoscale geochemical analysis of a framboidal magnetite grain within the Tagish Lake carbonaceous chondrite to demonstrate that the interlocking crystal arrangement formed within a sodium-rich, alkaline fluid environment. Notably, we report on the discovery of Na-enriched subgrain boundaries and nanometer-scale Ca and Mg layers surrounding individual framboids. These interstitial coatings would yield a surface charge state of zero in more-alkaline fluids and prevent assimilation of the individual framboids into a single grain. This basic solution would support rapid synthesis and racemization rates on the order of years, suggesting that the low abundances of amino acids in Tagish Lake cannot be ascribed to fluid chemistry.

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