Different rock dating methods
Tilting and erosion of the older rocks took place during this time, and if there was any deposition going on in this area, the evidence of it is now gone.
Figure 8.8 The great angular unconformity in the Grand Canyon, Arizona.
For example, the principle of superposition states that sedimentary layers are deposited in sequence, and, unless the entire sequence has been turned over by tectonic processes or disrupted by faulting, the layers at the bottom are older than those at the top.
The principle of inclusions states that any rock fragments that are included in rock must be older than the rock in which they are included.
The tilted rocks at the bottom are part of the Proterozoic Grand Canyon Group (aged 825 to 1,250 Ma).
The flat-lying rocks at the top are Paleozoic (540 to 250 Ma).
C-14 is produced when high-energy particles from solar radiation hit the earth’s atmosphere and make the unstable element called C-14.
As time goes by, this C-14 slowly changes back to stable atoms.
The image is about 7 m across.) [SE photo] An unconformity represents an interruption in the process of deposition of sedimentary rocks.The Proterozoic rocks of the Grand Canyon Group have been tilted and then eroded to a flat surface prior to deposition of the younger Paleozoic rocks.The difference in time between the youngest of the Proterozoic rocks and the oldest of the Paleozoic rocks is close to 300 million years.For example, a xenolith in an igneous rock or a clast in sedimentary rock must be older than the rock that includes it (Figure 8.6).Figure 8.6a A xenolith of diorite incorporated into a basalt lava flow, Mauna Kea volcano, Hawaii.