The Geomagnetic Polarity Time Scale (GPTS) has been constructed from an analysis of magnetic anomalies measured over the ocean basins and tying these anomalies to known and dated magnetic polarity reversals found on land. In general, positive anomalies represent periods when Earth's magnetic field was pointing north as it is today, while negative anomalies represent periods in Earth's history when Earth's magnetic field pointed to the south pole. The first marine magnetic anomaly based timescale was constructed by Jim Heirtzler and colleagues in 1968. Most recently the timescale has been tuned or adjusted for Earth's orbital variations and climatic response as measured in marine sediment records. The presently accepted timescale that is in most widespread use is the Cande and Kent 1995 timescale. The present timescale extends back to approximately 155 million years with potential extension in age to about 175 million years (Jurassic age) from the oldest ocean crust in the world (Click here to see my research into Jurassic-aged ocean crust). Shown below are figures of some timescales plus some ascii files with the age of the chrons.

 The Cande and Kent 1995 GPTS is the currently accepted timescale for the Cenozoic period (0 to 84 million years). It is based on the South Atlantic magnetic anomaly sequence and attempts to make the sea-floor spreading history smoothly varying over this region and then uses this timescale to fit the rest of the world's midocean ridge spreading systems. Black represents normal polarity, white represents reversed polarity.
 
 
 

Reference: Cande, S.C. and D.V. Kent, Revised calibration of the geomagnetic polarity timescale for the late Cretaceous and Cenozoic, J. Geophys. Res., 100, 6,093-6,095, 1995.
 Table of ages for Cande and Kent GPTS  

The 1986 Kent and Gradstein GPTS encompasses both the Cenozoic period and Jurassic periods (0 to 155 million years). The Cenozoic part has now been superceded by the Cande and Kent 1995 GPTS. Black represents normal polarity, white represents reversed polarity.
 
  Reference:Kent, D.V., and F. M. Gradstein, A Jurassic to recent chronology, in The Geology of North America, vol. M, The Western North Atlantic Region, edited by P.R. Vogt and B.E. Tucholke, pp 45-50, Geological Soc. of America, Boulder, Colo., 1986.
 Table of ages for Kent and Gradstein GPTS
 
 

The Huestis and Acton GPTS slightly modifies the Cande and Kent 1995 GPTS by minimizing spreading over the entire globe instead of just using the South Atlantic record. Black represents normal polarity, white represents reversed polarity.
 
 
  Reference:Huestis, S.P. and G.D. Acton, On the construction of geomagnetic timescales from non-prejudical treatment of magnetic anomaly data from multiple ridges, Geophys. J. Int., 129, 176-182, 1997.
 Table of ages for Huestis and Acton GPTS

 
  The Heirtzler et al GPTS was the original timescale based on the extrapolation of terrestial reversal records to magnetic anomalies. They used the South Atlantic magnetic anomaly record as the basis for tie points. Black represents normal polarity, white represents reversed polarity.
 
  Reference:Heirtzler, J. R., Dickson, G. O., Herron, E. M., Pittman III, W. C., and LePichon, X., Marine magnetic anomalies, geomagnetic field reversals, and motions of the ocean floor and continents, J. Geophys. Res., 73, 2119-2136, 1968.
 Table of ages for Heirtzler et al. GPTS

General references

Opdyke, N.D., and J.E.T. Channell, Magnetic Stratigraphy, Academic press, pp343, 1996.

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Last revised: 2007/5/4