Chris Eastoe grew up on a farm along Illawarra Road outside Longford, and for much of his adult life that was about as close to Tasmania as his career would get. He spent his professional years at the University of Arizona in Tucson, where he became one of the world's leading isotope geochemists, mapping the hidden plumbing of desert aquifers, pioneering new techniques in chlorine isotope analysis and running a carbon dating laboratory that could reach back through centuries of geological time. The work that defined those decades was far from abstract. Tucson sits atop a vast alluvial basin that,...