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.
Various theories as to the cause of this extinction have been suggested, ranging from a huge asteroid striking the earth to changes in global sea levels and climate to sustained periods of volcanism.
However, the method used by Simonetti and his colleagues determined that the New Mexico plant eating dinosaur was alive roughly 700,000 years after the surmised giant extinction event.
Although the challenge to the accepted dinosaur extinction model has received the most attention, Simonetti believes that the dating method described in the paper is especially significant.
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.