Radioactive isotopes in dating the past dating sites in thaiand
This is the principle of original horizontality: layers of strata are deposited horizontally or nearly horizontally (Figure 2).
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.
Second, it is possible to determine the numerical age for fossils or earth materials.
As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.The study of strata is called stratigraphy, and using a few basic principles, it is possible to work out the relative ages of rocks.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).In the Grand Canyon, the layers of strata are nearly horizontal.