Dating changes ze out dating
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.Geologists have established a set of principles that can be applied to sedimentary and volcanic rocks that are exposed at the Earth's surface to determine the relative ages of geological events preserved in the rock record.For example, in the rocks exposed in the walls of the Grand Canyon (Figure 1) there are many horizontal layers, which are called strata.These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing.As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.Second, it is possible to determine the numerical age for fossils or earth materials.Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time.
Each time a new layer of sediment is deposited it is laid down horizontally on top of an older layer.
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.
Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).
The principle of superposition builds on the principle of original horizontality.