Cougar dating techniques
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
Accordingly, the oldest rocks in a sequence are at the bottom and the youngest rocks are at the top.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.The age of the fossil must be determined so it can be compared to other fossil species from the same time period.Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.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.
The layers of rock at the base of the canyon were deposited first, and are thus older than the layers of rock exposed at the top (principle of superposition).
In the Grand Canyon, the layers of strata are nearly horizontal.
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.
Second, it is possible to determine the numerical age for fossils or earth materials.