What is the definition of relative age dating
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.Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time.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.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.
Each time a new layer of sediment is deposited it is laid down horizontally on top of an older layer.
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.
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
Younger layers are deposited on top of older layers (principle of superposition).