Dating in exposed and surface contexts
Sometimes sedimentary rocks are disturbed by events, such as fault movements, that cut across layers after the rocks were deposited.This is the principle of cross-cutting relationships.Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).The principle of superposition builds on the principle of original horizontality.Third, magnetism in rocks can be used to estimate the age of a fossil site.
Thus, any deformations of strata (Figures 2 and 3) must have occurred after the rock was deposited.
A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved.
However, by itself a fossil has little meaning unless it is placed within some context.
The principle states that any geologic features that cut across strata must have formed after the rocks they cut through (Figures 2 and 3).
According to the principle of original horizontality, these strata must have been deposited horizontally and then titled vertically after they were deposited.
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.