1 PHYSICAL SCIENCES: Geology Calcium isotope constraints on the end-Permian mass extinction Jonathan L. Payne 1* , Alexandra V. Turchyn 2 , Adina Paytan 3 , Donald J. DePaolo 4 , Daniel J. Lehrmann 5 , Meiyi Yu 6 , Jiayong Wei 7 1- Department of Geological & Environmental Sciences, Stanford University, 450 Serra Mall, Bldg. 320, Stanford, CA 94305, USA. 2- Department of Earth Sciences, Cambridge University, Downing Street, Cambridge, CB2 3EQ, UK. 3- Institute of Marine Sciences, University of California Santa Cruz, Santa Cruz, CA 95064, USA. 4- Department of Earth and Planetary Science, University of California - Berkeley, 301 McCone Hall, Berkeley, CA 94720-4767, USA. 5- Department of Geology, University of Wisconsin - Oshkosh, 800 Algoma Blvd., Oshkosh, WI 54901, USA. 6- College of Resource and Environment Engineering, Guizhou University, Caijiaguan, Guiyang 550003, Guizhou Province, China. 7- Guizhou Geological Survey, Bagongli, Guiyang 550005, Guizhou Province, China. Corresponding author: Jonathan L. Payne, Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Bldg. 320, Stanford, CA 94305; ph: 650-725-1606; fax: 650-725-0979 Email: jlpayne@stanford.edu