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.
Members of the Paleochronology group presented their findings at the 2012 Western Pacific Geophysics Meeting in Singapore, August 13-17, a conference of the American Geophysical Union (AGU) and the Asia Oceania Geosciences Society (AOGS).
Since dinosaurs are thought to be over 65 million years old, the news is stunning - and more than some can tolerate.
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.
Their radiometric dating analysis of rock and ash samples indicates that the dinosaurs died out 66,038,000 years ago, plus or minus 11,000 years.
The findings of the researchers, from the Berkeley Geochronology Center and the University of California at Berkeley in the US, Glasgow University in the UK and Vrije University Amsterdam in the Netherlands, appear in the Feb. The new extinction date supports the theory that the Cretaceous-Tertiary extinction event, which killed off all dinosaurs except the birds, was caused by an asteroid or comet slamming into what is now Mexico, BBC News reported.
The revised date is no more than 33,000 years after an asteroid collision created a 110-mile-wide crater near the Mexican town of Chicxulub.
There has been wide agreement among paleontologists that dinosaurs became extinct roughly 65.5 million years ago.
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.