According to the law of superposition, as long as an area remains undeformed by outside forces, the deeper you go down through the layers of rock, the older they are.
So, if you know the ages of the layers in the parent and wall rocks, you can calculate the age of the layers in your subsided area or xenolith by matching them.
One way to find the age of a xenolith or subsidence area surrounded by volcanic debris is to correlate its layers with the layers of wall or parent rocks.
Stratigraphy is the study of sedimentary rock layers.
We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!
Learn how inclusions and unconformities can tell us stories about the geologic past.Igneous rocks form from eruptions of lava or magma.Metamorphic rock is formed by great pressure far below the Earth's surface.This method is based on the assumption (which nearly always holds true) that deeper layers of rock were deposited earlier in Earth's history, and thus are older than more shallow layers.The successive layers of rock represent successive intervals of time.Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.Relative dating requires an extensive knowledge of stratigraphic succession, a fancy term for the way rock strata are built up and changed by geologic processes.Geologists establish the age of rocks in two ways: numerical dating and relative dating.Numerical dating determines the actual ages of rocks through the study of radioactive decay.Since relative dating can easily be verified by superposition (the younger bed over the older one), intrusion (the intrusive being younger than the intrusive rock), and use of index fossils (younger fossils in a rock layer make that layer younger than another containing older fossils), relative dating can be confirmed right at the field using one's direct observation.It could also be immediately confirmed in the base office once maps and cross sections are updated and the rock units confirmed.Different methods have their own limitations, especially with regard to the age range they can measure and the substances they can date.A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.