Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
Thus, any deformations of strata (Figures 2 and 3) must have occurred after the rock was deposited.
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time.
Third, magnetism in rocks can be used to estimate the age of a fossil site.
Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.
Second, it is possible to determine the numerical age for fossils or earth materials.
Just as when they were deposited, the strata are mostly horizontal (principle of original horizontality).
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).
Younger layers are deposited on top of older layers (principle of superposition).