The Permian-Triassic extinction event (a.k.a. "The Great Dying") occurred 252 million years ago and is generally considered the largest mass extinction event in Earth's history. By comparing the diversity of fossilized life from before and after the extinction event, the geologic research community has estimated that 90-96% of all species went extinct during a 60,000 year period (plus or minus 50,000 years). The Permian extinction is believed to have been especially severe in the planet's oceans.
However, a new paper, published by Steven Stanley from the University of Hawaii in The Proceedings of the National Academy of Sciences, challenges this traditional understanding. Stanley, using no new data but instead a different mathematical method to calculate extinction rates, argues that the Permian extinction may have only wiped out about 81% of all species on Earth.
His new argument centers on background extinction rates–the amount of species going extinct on a regular basis, even when no major extinction event is underway. Stanley calculates the background extinction rate for the middle and late Permian geologic era and then subtracts that from the extinction rates of the Permian extinction event. He also makes several other mathematical adjustments, but, essentially, he's discounting species that likely went extinct before the Permian extinction or that would have gone extinct during that time period, even if not major extinction event were happening.
With these calculations, the new rate of extinction during the Permian-Triassic extinction event is approximately 81% of all species. This is still a drastic reduction in biodiversity on Earth, but not as severe as previously thought.
Stanley's idea is certainly new and controversial within the geologic community. It will take time to see how the scientific consensus on "The Great Dying" evolves.