Relative dating wikipedia

For example, if a fault were truncated by an unconformity, and that unconformity cut by a dike.Based upon such compound cross-cutting relationships it can be seen that the fault is older than the unconformity which in turn is older than the dike.In other words, these relationships have various scales.A cartographic crosscutting relationship might look like, for example, a large fault dissecting the landscape on a large map.Periodically, the magnetic field of the earth reverses leaving a magnetic signal in volcanic and sedimentary rocks.

Sir Flinders Petrie, the younger contemporary of archaeologist Augustus Pitt-Rivers, was meticulous in his excavations and recorded every artifact and detail on site.Trees usually add growth rings on a yearly basis, with the spacing of rings being wider in high growth years and narrower in low growth years.Patterns in tree-ring growth can be used to establish the age of old wood samples, and also give some hints to local climatic conditions.For example, if a layer of sediment containing a fossil of interest is bounded on the top and bottom by unconformities, where the lower unconformity truncates dike A and the upper unconformity truncates dike B (which penetrates the layer in question), this method can be used.