Janne Blichert-Toft is a geochemist specializing in radiogenic isotopes and their applications to geochronology, planetary differentiation and, particularly, the evolution of the crust-mantle system of Earth. She is the acknowledged leader in geochemistry who advanced the measurement and application of the lutetium-hafnium (Lu-Hf) isotope system in geochemistry, cosmochemistry and planetary science and showed the enormous power of this isotope system to study the origin and evolution of planetary bodies, including Earth. Janne’s enthusiasm for research; her creativity to study geological processes recorded in rocks, minerals and fluids; and her energy and patience to advance analytical methods have made her a globally recognized expert in geochemistry and chemical geodynamics. Her main research approach includes the development and subsequent use of high-precision isotope measurements to reconstruct the origin of planetesimals and planets and, foremost, Earth’s evolution. Janne has developed key techniques for high-precision isotopic measurements, in particular by plasma source mass spectrometry. After developing and improving this significant new tool, she immediately realized the exceptional suitability of the Lu-Hf isotope system to advance our understanding of the formation of planets and their subsequent evolution, particularly, its power for revealing the dynamic geochemical processes in the silicate Earth through time as expressed through plate tectonics. Current models for the evolution of the crust-mantle system are heavily based on her research. It is to her credit that Lu-Hf became the key isotope system now used routinely and dominantly as a tracer of crustal growth and recycling. In addition to Hf isotopes, she has applied multiple radioisotope systems to geoscientific questions, particularly uranium-lead and samarium-neodymium. She used these systems for an enormous diversity of research topics, ranging from dating the formation of rocky bodies in the solar system to mineral growth in metamorphic rocks, formation of oil and the reconstruction of the paths of metals over human history. Many of her papers are seminal in the true sense of the word, as they initiated new research opportunities and directions and enormously influenced the path of geochemistry and cosmochemistry in the last two decades. These innovative and original scientific contributions made her an acknowledged authority in geochemistry who advanced the field significantly and made her one of the top-cited geochemists. Based on her far-reaching and prolific, deep and broad scientific achievements and her service to the science community, she is undoubtedly a worthy and deserving recipient of the Harry H. Hess Medal. — Klaus Mezger Universität Bern Bern, Switzerland

Madam President of AGU Susan Lozier, Members and Fellows of AGU, Colleagues, Friends, Family, Ladies and Gentlemen. Thank you, Klaus, for your kind and generous words, which touch me deeply. It is with great pleasure and pride that I receive the 2022 Harry H. Hess Medal from the American Geophysical Union. I am deeply honored and moved and profoundly humbled to join the ranks of the impressive list of distinguished past recipients of this award, many of whom have been my scientific role models since I was a student and have influenced me greatly. I am overwhelmed by the decades of groundbreaking science that the Hess Medal recognizes and how, by way of this reward, I am now linked to the preeminent Harry Hess of plate tectonic revolution fame known to every geologist. Moreover, AGU was the first professional society I joined 35 years ago, while still an undergraduate student, and Fall AGU was the first international conference I attended and where I, in an utterly nervous state, gave my first oral presentation, so it is very special, symbolic and meaningful to me to be honored today by AGU, especially as a European woman. I would like to thank AGU; the Hess Medal Committee members; my nominators; my employer, the CNRS (Centre National de la Recherche Scientifique), for daring what, at the time, seemed a great leap to hire me in France; my host institution, the École Normale Supérieure de Lyon, for having stood by me ever since; my second home, Rice University, for having adopted me into their Earth and planetary science family; my kind, generous, talented and brilliant students, who never cease to amaze, awe and inspire me by their achievements, creativity, intelligence and scientific rigor; our outstanding technical staff; and my wonderful colleagues and collaborators worldwide, many of whom have become close friends over the years. I would not be the scientist I am today without all of you. Lastly, I am forever grateful to my husband and my parents, without whose wisdom, integrity and boundless love and support I would not have made it this far intact because, as we all know, being successful in academia is a tough challenge at many levels, and not only for women…not anymore. Thank you, Madam President, thank you, AGU, thank you all again so very much for this exquisite and unique honor! — Janne Blichert-Toft École Normale Supérieure de Lyon and CNRS Lyon, France

For being the world's leading geochemist in the application of hafnium isotopes to the evolution of the Earth and the early solar system.