简介：GeologictimeisfundamentaltotheEarthSciences,andprogressinmanydisciplinesdependscriticallyonourabilitytomeasuretimewithincreasingaccuracyandprecision.Isotopicgeochronologymakesuseofthedecayofradioactivenuclidesasahelptoquantifythehistoriesofrock,minerals,andothermaterials.Bothaccuracyandprecisionofradioisotopicagesare,atpresent,limitedbythoseofradioactivedecayconstants.Modemmassspectrometerscanmeasureisotoperatioswithaprecisionof10-4orbetter.Ontheotherhand,theuncertaintiesassociatedwithdirecthalf-lifedeterminationsare,inmostcases,stillatthepercentlevel.ThepresentshortnotebrieflysummarizesprogressandproblemsthathavebeenencounteredduringtheWorkingGroup'sactivity.