Geologic time rock dating
In the diagram to the right,the fault cuts the limestone and the sandstone, but does not cut the basalt.Thus we know that the fault is younger than the limestone and shale, but older than the basalt above.He concluded that process that are currently operating on the Earth must be the same processes that operated in the past.This principle is often stated as "the present is the key to the past".
We discuss the 7 principles of stratigraphy first and then see how these apply to fossils.
From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.
How do we know this and how do we know the ages of other events in Earth history?
Thus, in a sequence of layers that have not been overturned by a later deformational event, the oldest layer will be on the bottom and the youngest layer on top.
This is the same principle used to determine relative age in the trash pits discussed previously.