Dating uses properties
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.By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.The principle of superposition states that in an undeformed sequence of sedimentary rocks, each layer of rock is older than the one above it and younger than the one below it (Figures 1 and 2).Accordingly, the oldest rocks in a sequence are at the bottom and the youngest rocks are at the top.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." First, the relative age of a fossil can be determined.Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.
Thus, any deformations of strata (Figures 2 and 3) must have occurred after the rock was deposited.
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 of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
Younger layers are deposited on top of older layers (principle of superposition).
Search for dating uses properties:
The age of the fossil must be determined so it can be compared to other fossil species from the same time period.