Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.These skeptics do not provide scientific evidence for their views.The diagram right shows two distinct faunal assemblages.What can be deduced from our two distinct faunas in terms of their usefulness in the relative dating of rocks?However, the assumption of contemporaneity may not always be correct.This is due to the fact that one or both of the objects may have been moved or redeposited into a different location.
Uranium is present in many different rocks and minerals, usually in the form of uranium-238.
However, relative methods are , which is that if there are layers of deposits, those laid down first will be on the bottom and those laid down last will be on the top. However, geological strata are not always found to be in a neat chronological order.
Wind and water erode strata and some areas are uplifted or even tilted.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.