Dating of the triassic period
Meishan is one of the best-preserved records of the mass extinction, as well as the transition between the Permian and the following Triassic Period.
Burgess said the rocks were all analyzed in the same lab, on the same machine, with the same chemicals and by the same lab tech — all to minimize that extra few thousand years of error that scientists must report when estimating rock ages.
Sixty Permian species disappear in the Penglaitan extinction layer.
Burgess and his colleagues attacked the timing problem with a high-resolution, uranium-lead dating technique.
The team tested volcanic rocks from the Siberian Traps and marine rocks from Meishan, China.
Burgess's new age for Meishan's Bed 25 (a thin rock layer that is the global reference point for the onset of extinction) is 251.941 million years ago, plus or minus 37,000 years.
And volcanism started at the Siberian Traps 252.28 million years ago, plus or minus 11,000 years, Burgess said.