One particular Precambrian layer known as the Cardenas Basalt has been dated by radiometric methods to about 1.1 billion years in age.
The Cenozoic flows sampled by ICR thus are claimed to yield an age which is about 200 million years older than the Cardenas Basalt.
The walls of the canyon are mostly cut into horizontal rock layers of Paleozoic age (green in Figure 1, above).
The ICR's Grand Canyon Dating Project does not strike a telling blow against the reliability of isochron dating.The conditions which caused the "false isochron" in this case are fairly well-understood, and easy to avoid by proper sample selection.The attempt to abuse the meaning of a single contrived date -- which was produced only by a sample selection geared to dating a different event, and only for samples whose results were known by Austin in advance -- says a lot more about the level of competence or honesty in this creation "science" research program, than it says about the validity of isochron dating methods.Even if given credit for discovering this case (which he clearly doesn't deserve, as his use of Leeman's data proves), Austin has only managed to "call into question" a particular sampling technique.An angular unconformity is the result of tilting and eroding of the lower layers before the upper ones are deposited.
These tilted and eroded layers are Precambrian in age (blue in Figure 1, above).In fact, the resulting age in this case may well be meaningful and accurate.The problem is not the age itself but rather Austin's sleight-of-hand in trying to pass off the result as necessarily the age of the flows rather than a minimum age of their source.If it is not the flows' age, that is not a "problem" with isochron dating, and it is not relevant to the large number of Rb/Sr isochrons which were computed from mineral separations of a single object.At the GSA meeting, Austin discussed the inheritance of a mantle age.The canyon must be younger than the rock layers that it cuts into.