<P> Until 2000, it was thought that rock sequences spanning the Permian--Triassic boundary were too few and contained too many gaps for scientists to reliably determine its details . However, it is now possible to date the extinction with millennial precision . U--Pb zircon dates from five volcanic ash beds from the Global Stratotype Section and Point for the Permian--Triassic boundary at Meishan, China, establish a high - resolution age model for the extinction--allowing exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales . The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Ma, a duration of 60 ± 48 ka . A large (approximately 0.9%), abrupt global decrease in the ratio of the stable isotope C to that of C, coincides with this extinction, and is sometimes used to identify the Permian--Triassic boundary in rocks that are unsuitable for radiometric dating . Further evidence for environmental change around the P--Tr boundary suggests an 8 ° C (14 ° F) rise in temperature, and an increase in CO levels by 6997200000000000000 ♠ 2000 ppm (for comparison, the concentration immediately before the industrial revolution was 6996279999999999999 ♠ 280 ppm .) There is also evidence of increased ultraviolet radiation reaching the earth, causing the mutation of plant spores . </P> <P> It has been suggested that the Permian--Triassic boundary is associated with a sharp increase in the abundance of marine and terrestrial fungi, caused by the sharp increase in the amount of dead plants and animals fed upon by the fungi . For a while this "fungal spike" was used by some paleontologists to identify the Permian--Triassic boundary in rocks that are unsuitable for radiometric dating or lack suitable index fossils, but even the proposers of the fungal spike hypothesis pointed out that "fungal spikes" may have been a repeating phenomenon created by the post-extinction ecosystem in the earliest Triassic . The very idea of a fungal spike has been criticized on several grounds, including: Reduviasporonites, the most common supposed fungal spore, was actually a fossilized alga; the spike did not appear worldwide; and in many places it did not fall on the Permian--Triassic boundary . The algae, which were misidentified as fungal spores, may even represent a transition to a lake - dominated Triassic world rather than an earliest Triassic zone of death and decay in some terrestrial fossil beds . Newer chemical evidence agrees better with a fungal origin for Reduviasporonites, diluting these critiques . </P> <P> Uncertainty exists regarding the duration of the overall extinction and about the timing and duration of various groups' extinctions within the greater process . Some evidence suggests that there were multiple extinction pulses or that the extinction was spread out over a few million years, with a sharp peak in the last million years of the Permian . Statistical analyses of some highly fossiliferous strata in Meishan, Zhejiang Province in southeastern China, suggest that the main extinction was clustered around one peak . Recent research shows that different groups became extinct at different times; for example, while difficult to date absolutely, ostracod and brachiopod extinctions were separated by 670 to 1170 thousand years . In a well - preserved sequence in east Greenland, the decline of animals is concentrated in a period 10 to 7001600000000000000 ♠ 60 thousand years long, with plants taking an additional several hundred thousand years to show the full impact of the event . An older theory, still supported in some recent papers, is that there were two major extinction pulses 9.4 million years apart, separated by a period of extinctions well above the background level, and that the final extinction killed off only about 80% of marine species alive at that time while the other losses occurred during the first pulse or the interval between pulses . According to this theory one of these extinction pulses occurred at the end of the Guadalupian epoch of the Permian . For example, all but one of the surviving dinocephalian genera died out at the end of the Guadalupian, as did the Verbeekinidae, a family of large - size fusuline foraminifera . The impact of the end - Guadalupian extinction on marine organisms appears to have varied between locations and between taxonomic groups--brachiopods and corals had severe losses . </P> <Table> <Tr> <Th> Marine extinctions </Th> <Td> Genera extinct </Td> <Td> Notes </Td> </Tr> <Tr> <Td_colspan="5"> Arthropoda </Td> </Tr> <Tr> <Td> Eurypterids </Td> <Td> 100% </Td> <Td> May have become extinct shortly before the P--Tr boundary </Td> </Tr> <Tr> <Td> Ostracods </Td> <Td> 59% </Td> <Td> </Td> </Tr> <Tr> <Td> Trilobites </Td> <Td> 100% </Td> <Td> In decline since the Devonian; only 2 genera living before the extinction </Td> </Tr> <Tr> <Td_colspan="5"> Brachiopoda </Td> </Tr> <Tr> <Td> Brachiopods </Td> <Td> 96% </Td> <Td> Orthids and productids died out </Td> </Tr> <Tr> <Td_colspan="5"> Bryozoa </Td> </Tr> <Tr> <Td> Bryozoans </Td> <Td> 79% </Td> <Td> Fenestrates, trepostomes, and cryptostomes died out </Td> </Tr> <Tr> <Td_colspan="5"> Chordata </Td> </Tr> <Tr> <Td> Acanthodians </Td> <Td> 100% </Td> <Td> In decline since the Devonian, with only one living family </Td> </Tr> <Tr> <Td_colspan="5"> Cnidaria </Td> </Tr> <Tr> <Td> Anthozoans </Td> <Td> 96% </Td> <Td> Tabulate and rugose corals died out </Td> </Tr> <Tr> <Td_colspan="5"> Echinodermata </Td> </Tr> <Tr> <Td> Blastoids </Td> <Td> 100% </Td> <Td> May have become extinct shortly before the P--Tr boundary </Td> </Tr> <Tr> <Td> Crinoids </Td> <Td> 98% </Td> <Td> Inadunates and camerates died out </Td> </Tr> <Tr> <Td_colspan="5"> Mollusca </Td> </Tr> <Tr> <Td> Ammonites </Td> <Td> 97% </Td> <Td> </Td> </Tr> <Tr> <Td> Bivalves </Td> <Td> 59% </Td> <Td> </Td> </Tr> <Tr> <Td> Gastropods </Td> <Td> 98% </Td> <Td> </Td> </Tr> <Tr> <Td_colspan="3"> Retaria </Td> </Tr> <Tr> <Td> Foraminiferans </Td> <Td> 97% </Td> <Td> Fusulinids died out, but were almost extinct before the catastrophe </Td> </Tr> <Tr> <Td> Radiolarians </Td> <Td> 99% </Td> <Td> </Td> </Tr> </Table>

The largest mass extinction in earth's history occurred at the end of which era