.. . . .Yes radiometric age-dating om zircon (and other minerals) works well. . . . but remember that we are dating the age of the 'zircon' (when it crystallized). If the host rock has been 'recycled' (e.g., metamorphosed, etc.) or the zircon has re-crystallized, or otherwise the U-Pb ratio 'reset' . . . the original host rock may actually be older than indicated. Also, there are arguments made that 'loss' of radiometric components may indicate a younger age Maximum age of the earth is determined by finding (and reporting) the radiometrically-'oldest' (via U-Pb) zircons. We perhaps need to look at zircons, etc. in some meteorites?
wlminex
Yes, "the original host rock may actually be older than indicated." The oldest known rocks give the lower limit of the age of the earth. A possibility of finding an even older rock should not be ignored.
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Ludwik Kowalski (see Wikipedia)
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