Argon argon radioactive dating method
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.
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.
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
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.
Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).
Each time a new layer of sediment is deposited it is laid down horizontally on top of an older layer.In addition to being tilted horizontally, the layers have been faulted (dashed lines on figure).Applying the principle of cross-cutting relationships, this fault that offsets the layers of rock must have occurred after the strata were deposited.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).