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  • Geological timescales are the frameworks that geologists use to assign ages to units of rock. This is probably one of the most fundamental concepts in geology and its allied fields, including paleontology and evolutionary studies. It is a basic requirement for many things, such as: • assigning geological age to rocks, fossils and economic minerals; • calibrating the rates of geological processes such as fault displacement and plate rotation, submergence, uplift and erosion of the land, earthquake frequency and volcanic activity; • measuring rates of climate change, sea-level change, biodiversity change and organic evolution; • the search for natural resources. Age indicators used to develop timescales are various, but the oldest and still most frequently used approach is to recognise rocks of similar age by the fossils they contain. The first geological timescales were developed in Europe, and these are gradually being consolidated into an international geological timescale which is expanded and updated every few years. Many areas of the world, however, have highly endemic fossils – just as countries like New Zealand have highly endemic plant and animal biotas today – and it is hard to relate the geology of these places to the international framework. Like many of these places, New Zealand uses the international scheme for the major units (Jurassic, Cretaceous, and so on) and for rocks which are not well represented in our own country, but adopts a more convenient local scheme, based on our own endemic fossils, for the smaller time divisions. Our New Zealand geological timescale has been under development since the earliest days of geological research in the country, in the late nineteenth century, although perhaps the greatest advances occurred through the 1940s to 1960s. A huge amount of related knowledge was collected together and published in 2004, in a monograph edited by Roger Cooper and published by GNS Science. Access is available online from the GNS Science web site. Like all scientific endeavours, timescales are continually revised as new knowledge comes to hand. Most commonly, these revisions apply to the absolute age calibrations of the time units. Although fossils are a useful way to quickly tell that two different bodies of rock are of similar age, they cannot – on their own – tell us exactly how old that is. Various events, such as the “first” (oldest) occurrence of a particular fossil shell, have to be calibrated using some technique, such as radiometric dating, to find out how many years ago the event took place. Unfortunately, calibration usually requires that numerous factors happen to be “just right” in order to be accurate. Consequently, new data comes to hand slowly, over many years. DOI: https://doi.org/10.21420/F49B-4G37 Cite data as: GNS Science. (2004). New Zealand Geological Timescale [Data set]. GNS Science. https://doi.org/10.21420/F49B-4G37