Acknowledgments
We thank Laura Córdoba, Chiara Bordier, Raul Machado and Anja Wulf for technical support in the lab, and Anika Lehmann, Marie Spohn and Alexander Tischer for their valuable input for the development of the experimental design. Philip Hoelzmann and Manuela Scholz helped with elemental analyses. MCR acknowledges funding from an ERC Advanced Grant (694368).