The foreign object is thus older than the sedimentary rock because it was there before the sediment that formed the rock.
A simple way to remember this term is to think that an inclusion represents something being included in the rock that wouldn’t have been otherwise.
They occur where layers of rock were either eroded away or never deposited and cemented in the first place.
Sometimes there is evidence that an unconformity has occurred; other times, there is no way of knowing if there is a break in the relative time scale.
There are several important principles in relative dating, which we will discuss below.
The law of faunal succession deals with the fossils of plants and animals and states that groups of fossilized animals and plants follow or succeed each other in a predictable manner.
The law of lateral continuity states that the deposition of sediment is continuous unless there is a barrier or subsequent changes in the landscape break up layers.
This can be a challenging concept to understand, but if you imagine a basin where sediment is deposited, this principle states that the sediment will be equally deposited in this area until there is no more sediment or until the sediment reaches the edge of the basin or another barrier.
Smaller marine organisms are also limited in geologic time because they are often sensitive to environmental changes making them a boom-and-bust kind of organism.
That is, they become abundant, and then their sensitivity to environmental changes causes them to become extinct.