In the last four years, remarkable progress has been made in
the recalibration of the GPTS. The most dramatic advances have
been in the field of astrochronology which has been used to provide
ages for Late Miocene-Quaternary reversals with a precision of a
few tens of thousands of years, less than an order of magnitude
greater than the time for the process of reversal to occur. These
studies have opened the door to astrochronological calibration of
the pre-Late Miocene GPTS if suitable sections can be found on land
or recovered by ocean drilling. The second important advance has
been in the field of radiometric dating. 
Ar/
Ar and U/Pb
zircon methods now provide a level of precision which makes most
previous age determinations redundant. In the last few years,
numerous 
Ar/
Ar age determinations have ratified the
Plio-Pleistocene astrochronology. Renne et al. [1994] have taken
the next step and used the the astrochronology to calibrate the
Ar/
Ar dating standard (Fish Canyon sanidine, Mmhb-1),
thereby reducing the uncertainty to 0.6% for 
Ar/
Ar ages
calibrated against this standard.
Acknowledgments. I thank K. Verosub and two anonymous reviewers for comments on an earlier version of this paper.