how are absolute dating and relative dating alike - Besides being distinctive, a volcanic-ash layer has four other advantages for purposes of correlation: it was laid down in an instant of geologic time; it settles out over tremendous areas; it permits physical correlation between contrasting sedimentary environments; and unaltered mineral crystals that permit radiometric measurements of absolute age often are present. From an examination of such outcrops with special focus on the sequence of animal forms comes the empirical generalization that the faunas of the past have followed a specific order of succession, and so the relative age of a fossiliferous rock is indicated by the types of fossils it contains. The other two isotopes in comparison are more common than carbon-14 in the atmosphere but increase with the burning of fossil fuels making them less reliable for study (2); carbon-14 also increases, but its relative rarity means its increase is negligible. Follow up on what sarah said, the amount of dates from terrestrial vs marine rocks is about the same, but because the timescale was defined using marine biostratigraphy, people have tended to target marine rocks first for radioisotopic dating.
Relative and absolute dating notes for Mrs. Fulmer's Life Science Class.