Ross Taylor was born in New Zealand and is now an Emeritus Professor at the Australian National University. He is a trace element geochemist and carried out the initial analysis of the first lunar sample returned to Earth at NASA, Houston in 1969. He has a D.Sc. from the University of Oxford, is a Foreign Member of the US National Academy of Sciences. and has received the Goldschmidt Medal of the Geochemical Society, the Leonard Medal of the Meteoritical Society and the Bucher Medal of the American Geophysical Union. He is the author of six other books including Solar System Evolution, Second edition (Cambridge University Press, 2001). Asteroid 5670 is named Rosstaylor in his honour. Scott M. McLennan is Professor of Geochemistry at the State University of New York at Stony Brook. He conducts research into the geochemistry of sedimentary rocks, and has published 140 papers in the fields of geochemistry, planetary science and sedimentology. Since 1998, he has applied laboratory experiments and data returned from missions to Mars to understand the sedimentary processes of that planet, and is on the science teams of the 2003 Mars Exploration Rover and 2001 Mars Odyssey missions. He received a Presidential Young Investigator Award from the National Science Foundation in 1989 and a NASA Group Achievement Award as part of the Mars Exploration Rover Science Operations Team in 2004.