Paul Henderson is an Honorary Professor in the Department of Earth Sciences at University College London and was previously Head of the Department of Mineralogy and Director of Science at the Natural History Museum. He was President of the Mineralogical Society of Great Britain and Northern Ireland (1990–2) and Vice President of the Geological Society of London (2002–8). Professor Henderson's research interests focus on the geochemistry of igneous and related rocks, and he is the author of the textbook Inorganic Geochemistry (1982) and the editor of Rare Earth Element Geochemistry (1984). Gideon Henderson is Professor of Earth Sciences at Oxford University and was previously an Associate Research Scientist at the Lamont Doherty Earth Observatory of Columbia University, New York. His research interests involve the application of geochemical tools to understand the Earth's surface environment including climate change, past ocean circulation, and geochemical fluxes from land to sea. Professor Henderson is also an editor of Uranium-Series Geochemistry (2003).