If it had happened before the layers had formed, then we wouldn't see it punching through all the layers; we would only see it going through the layers that had existed at the time that it happened. The Principle of Cross-Cutting Relationships states that rock formations that cut across other rocks must be younger than the rocks that they cut across.
The same idea applies to fault lines that slide rock layers apart from each other; a fault that cuts across a set of strata must have occurred after the formation of that set.
There may be a layer missing in the strata, or a set of sedimentary rock on top of metamorphic rock.
Let's look at these rock strata here: We have five layers total.Inclusions are always older than the sedimentary rock within which they are found.Other times, geologists discover patterns in rock layers that give them confusing information.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.