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Rather than employ the services of such a laboratory, it is so much cheaper for the geologist to recognize a well-known species of ammonite, trilobite, foraminiferan, or whatever, the age of which is already known.Instead, other methods are used to work out a fossil’s age.Accurate dates also allow us to create sequences of evolutionary change and work out when species appeared or became extinct. These are: Where possible, several different methods are used and each method is repeated to confirm the results obtained and improve accuracy.Different methods have their own limitations, especially with regard to the age range they can measure and the substances they can date.Since relative dating can easily be verified by superposition (the younger bed over the older one), intrusion (the intrusive being younger than the intrusive rock), and use of index fossils (younger fossils in a rock layer make that layer younger than another containing older fossils), relative dating can be confirmed right at the field using one's direct observation.It could also be immediately confirmed in the base office once maps and cross sections are updated and the rock units confirmed.In this article we shall discuss how fossils can be used for the purposes of absolute dating.We have already discussed the construction of the geological column.
Sedimentary rocks are rarely useful for dating because they are made up of bits of older rocks.During this process the pieces of the atom move apart at high speed, causing damage to the rock or mineral.This damage is in the form of tiny marks called fission tracks.There are three main advantages of using fossils for dating in this manner.
First of all, we may want to date a stratum which is a long way up or down from any rocks we can date using radiometric methods.Hence we can use datable rocks to put dates on fossil species; and then we can use the fossil species to put dates on other rocks which would otherwise be difficult to date.