ACTS & FACTS Vol. 33 No 10 October 2004 ii Discussion "Most people believe that when the different radioisotope dating methods are used on the same rock unit they yield the same age. However, the radioisotope dating of these Grand Canyon rocks clearly demonstrate that the disagreement, or isochron discordance, is pronounced. Even when calculated error margins are taken into account the different radioisotope dating methods yield completely different "agea" that cannot be reconciled----1240+_84 Ma (Rb-Sr), 1655+_40 Ma (Sm-Nd), and 1883+_53 Ma (Pb-Pb). None of the obtained isochron "ages" corresponds to the "date" for any recognized event, neither the original lava eruptions nor the subsequent metamorphism."