'The most incomprehensible thing about the world is that it is comprehensible.' ALBERT EINSTEIN, 1950 The tremendous progress of recent years in the field of isotopes in the earth sciences has proved invaluable in attempting to solve a varied spectrum of geological and geochemical problems. The lunar exploration programmes provided rocks for analysis, stimulating refinements in mass spectrometry which were later used for terrestrial samples too. Among significant advances was the development of electrostatic tandem accelerator mass spectrometers allowing the precise measure ment of abundances...