Dating the recent past

The dramatic environmental changes of the last 500 years are likely to continue into the future and to have an increasing impact on both the Earth and human society. Any understanding of future environmental change is thus critically dependent on our capacity to reconstruct the environmental changes of the past. Fundamental to this is an ability to place the environmental responses of the last half millennium within a reliable chronological framework. Unfortunately, this most recent part of the geological timescale presents us with some of the greatest challenges for dating. With the exception of 230Th/234U methods, whose use is restricted to the rather specific depositional environments of shallow marine and terrestrial carbonates, there is no established geochronometric tool capable of dating more than a fraction of the recent past at a resolution adequate to tackle the environmental issues of this period. This challenge has been met by refining existing procedures (including 14C, 40Ar/39Ar, event chronostratigraphy and optically stimulated luminescence) and developing new ones (such as 32Si). These offer a means of calibrating the high-resolution environmental records of the last 500 years and answering the critical environmental questions presented by this period.