There are different theories as to what caused the end-Permian mass extinction, it is thought that a number of different biological and physical causes led to extinction.

The first theory outlines that changes in the climate are responsible for the mass extinction. It is thought that there was a change in the carbon cycle, due to an increase in carbon dioxide from volcanoes along with the thermal decomposition of organic matter which releases CO2. The additional amount of carbon dioxide led to an increase in the overall temperature. This has been verified by the oxygen isotope records showing a high-temperature rise in the late Permian period.

Furthermore, the eruptions of the Siberian flood basalts have also been linked to the mass extinction event as the volcanic flow from this is found in the same beds where the extinction event occurred. the eruption of the Siberian flood basalts led to the input of a mass amount of carbon dioxide into the environment which furth impacted the temperature making it warmer due to the higher level of atmospheric greenhouse gases. The flood basalts could have in turn washed the organic, terrestrial materials into the marine environment which will have altered the carbon isotope ratios in the rock which has meant that the rocks possess conflicting data with a mix of both terrestrial and marine characteristics.

In order to date when the mass extinction event happened, U/Pb isotopic dating has been used to analyse the zircon populations which have been typically corrupted with postdepositional Pb loss. The findings most recently have shown that the base of the Triassic is 252.5 +/- 0.3 million years found by ash layer postdating from the Permian Triassic boundary, along with the maximum age of the mass extinction at 254 Ma on the foundations of incoherent data sets of an ash bed. The results from the dating the Permian Triassic boundary concluded that the Siberian volcanism was synchronous and that the extinction period occurred in a short amount of time, contrary to beliefs that it happened over a longer period of time and over generations of species.

In conclusion there are many different theories as to the cause of the greatest extinction of all time, however, it is widely thought that it is a combination of the climate change and increase in carbon in the atmosphere from the Siberian trap volcanoes all triggered the mass extinction event.

The short term effects of the End Permian Mass Extinction on the environment meant that the Earth was cold, dark and acid rain fell, these conditions alone would have killed off photosynthetic plants as well as plankton which are the basis of many food chains.

These conditions will have meant that the oxygen availability decreased and there was a rise in carbon in the atmosphere. This is clarified by the carbon volumes found in rocks from the time period, as found by P.R. Renne et al. (1995), a decrease in carbon isotope 13 by 5% is found in bed 24e at Meishan in South China, which lasts until bed 28 so therefore also shows that the Permian-Triassic boundary was around 252.28 Ma.

The anoxia and high levels of partial pressure carbon dioxide meant that the species did not die instantaneously but over a greater time period such as by reduced fertility rates and skeletal pathologies. Therefore the short term effects had long term consequences on the flora and fauna.

This also meant that organisms better adapted to the environmental conditions had a higher chance of survival, for example, polychaetes, which have the greatest tolerance to low oxygen environments.

Effects on some species were so drastic that they never recovered after the extinction, for example, the palaeozoic evolutionary fauna. Species that were benthic, sessile and in suspension-feeding communities were damaged immensely, such as, trilobites and brachiopod families. Terrestrial species were also affected especially the plant and vertebrate communities.