Kevin Rogers submitted a comment to that article (reproduced below, edited to focus on substantive issues), to which Dr Jim Mason replies.Radioactive Dating Methods I am Kevin Rogers and am the director of Reasonable Faith Adelaide.
is 100% of any lead excluded from the crystal or, perhaps, less than 100%).
Nor was there discussion about how well the experimental conditions that have been mentioned would have represented the situation within crystallizing magmas.
Jim raised some interesting points but I don’t believe that he addressed the central points that Justin raised.
Jim stated that “uranium is preferentially encased in these [zircon] crystals while lead is preferentially excluded” but did not fully explain the significance of this.
These results are consistent with proposals that suggest the appearance and popularization of rock art in various places in the Andes for the temporal transect of 3000–1000 BCE.
Finally, these new datings are added to the scant corpus of absolute dates for rock art that exist in South America.
At their request, physicist Dr Jim Mason, of CMI Canada, reviewed the material from the meeting and his response was published on 2 April 2015 (see Response to Geochronology: Understanding the Uncertainties, a presentation by Dr Justin Payne).
Furthermore, a recent article “Metallic lead nanospheres discovered in ancient zircons” says (in the introductory “Significance” section): “The heterogeneous distribution of Pb can, however, affect isotopic measurement by microbeam techniques, leading to spurious age estimates.” This raises significant questions for the technique and casts doubt over its robustness.
I did not discuss this technique because it seems a pretty straightforward combination of various parent-daughter relationships.
Last year we held a number of meetings on the young/old earth issue and gave YECs numerous opportunities to speak.