Igneous rocks numerical dating
Further confusion arises when one publication or geologist says, for example, that the Kaibab Formation is 270 m.y. The same questions arise for the other rock units at Grand Canyon. This article will answer these questions by providing a short primer on geologic dating methods and how they were applied to Grand Canyon rocks.
We then describe Grand Canyon rocks as belonging to three “sets,” or packages of rocks, each with unique geologic histories, and present a compilation of “best” numeric ages for Grand Canyon rocks to use when explaining Grand Canyon geology to the public.
There are younger geologic deposits in Grand Canyon too, such as the Ice Age fossils found in caves, a 1000-year-old lava flow in the western canyon, and even the debris flow deposits that continue form each year.
Yet, it is the canyon’s rock walls that allow people to develop their greatest perspective on geologic time, because of these rocks’ immense age, their fossil record, and because these rocks formed in environments far different than those found in northern Arizona today.
By doing this repeatedly, for many locations around the world, the geologic time scale has been established.
Relative dating determines the order in which a sequence of past events occurred, but does not determine exactly when the geologic events happened.
See Figure 1 for illustrations of other relative age relationships at Grand Canyon.
Correlation determines if rocks are the same age, and is a key tool that geologists use to identify the relative ages of rocks where a rock layer is not continuously exposed.
The absolute ages of the rocks have been determined through radiometric dating where possible.
Hence, the geologic time scale provides a calibrated "yardstick" for determining the ages of rocks worldwide through an examination of their fossils.
You can also learn about which beds were dated radiometrically, and the result.