| The geological timescale is the time framework by which
we date, correlate and classify rock formations and geological events.
It provides the time framework for all studies of the history of the
Earth and its life. It is used for assigning geological age to rocks,
fossils and economic minerals, and for 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. Rates of climate change, sea-level change, biodiversity
change and organic evolution also are measured in terms of the geological
timescale. Timescales play an important part in the search for petroleum
and coal resources. It is essential therefore, that we have the most
accurate and precise timescale available.
Dating rocks using fossils
is termed biostratigraphy. Biostratigraphy uses the succession of
species of animals and plants that are found in successive layers
of rock, or strata. Changes in fossil species through time have
resulted from evolution, migration and extinction. Both macrofossils,
such as molluscs, brachiopods and fossil plants, and microfossils,
such as foraminifera, radiolaria, and dinoflagellates are used.
Because New Zealand is relatively isolated from other regions of
the Earth, its succession of fossil species differs from that of
other regions. New Zealand therefore has its own geological time
scale that has been developed over many years. NZ Geological Timescale June 2003
(MS Excel spreadsheet file)
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