ABSTRACT
In the modern world a quite different time scale is equally taken for granted, at least among scientists. Geologists and other Earth scientists deal with time in almost equally vast quantities, but they also date a plethora of past events with a casual confidence and a sense of relative precision that recall Ussher's efforts. Ussher and his colleagues practised the seventeenth-century science of chronology; modern geologists practise the twentieth-century science of geochronology. The similarity of terms points to shared concepts and even methods. In the early nineteenth century, geologists – as they may now be called without anachronism – assumed, like de Luc, that the Earth's still earlier history was far longer, but unquantifiable. Leaving the magnitude of the timescale aside, they therefore concentrated on clarifying the sequences of rock formations. After the First World War geologists gradually came to appreciate that their own distinctive evidence did, in fact, support the longer timescale now offered by the physicists.
