Relative dating of fossils and rocks Free usan adult live webcam show
Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
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.
A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.
Correlating two separated outcrops means establishing that they share certain characteristics indicative of contemporary formation.
Obviously, the sedimentary rocks had to be there prior to emplacement of the igneous rocks, and thus they are older than the igneous rocks.New discoveries have filled in the gaps, and shown us in unimaginable detail the shape of the great ‘tree of life’.Darwin and his contemporaries could never have imagined the improvements in resolution of stratigraphy that have come since 1859, nor guessed what fossils were to be found in the southern continents, nor predicted the huge increase in the number of amateur and professional paleontologists worldwide.Furthermore, useful fossils are either rare or totally absent in rocks from Precambrian time, which constitutes more than 87 percent of Earth history.Precambrian rocks must therefore be correlated by means of precise isotopic dating.