After the extinction occurred estimates say only a third of land life remained and only 5% of sea life remained . The PTB event also had the longest recovery time of any mass extinction, lasting 5 million to 8 million years due to other, more minor, extinction events taking place after the Permian extinction (Erwin 1998). An abundance of Fungi found in boundary rocks and a lack of tree pollen found in these same rocks suggests an immediate increase of fungi’s just after the PTB event that fed off of the decaying tree matter, this was known as the ‘fungil spike’ (Visscher 2011). Research then suggests that oddly the top of the food chain recovered before the bottom half of the food chain. Usually it would be expected for the bottom part of a food chain to form the foundations to support the upper half of the food chain e.g. predators. However it’s estimated to have taken 5 million years for animals at the top of the food chain to emerge, but 50 million years for the underlying ecosystem to bounce back (Twitchett 2007). Reptiles were one of the quickest to recover; within a million years synapsid diversity recovered (Visscher 2011).
How the Mass Extinction is Dated
Until recently, the rock sequences spanning the Permian–Triassic boundary were seen as containing too many gaps for a small sample size and so reliable dating couldn’t be generated (Shen 2011). However though the use of Zircon populations in ash layers a much more accurate date can be calculated. These populations used to date still have issues however, for example Mundil (2004) looks at Zircon populations being affected by contamination of indistinguishable older Xenocrysts. Zircon’s are used as a more precise method of calculating the mass extinction but due to contamination, the exact date of the Permian Mass Extinctions found using Zircons is highly debated. One way to combat this contamination is to analyse single Zircon populations in which the problem of lead (Pb) loss has been removed by heating the populations to high temperatures, creating more reliable data from ash layers. However the aggressiveness of this technique often leads to less reliable results. The Zircon data leads to the conclusion that the biotic crisis occurred at 252.6 Ma and so the P-T boundary must be slightly younger (Mundil 2004). The P-T extinction exact date is still heavily debated however due to the reliability of much of the data.
Causes of the Permian Mass Extinction
Mundil (2004) suggests there are three scenarios to explain the mass extinction: a bolide impact, catastrophic climate change caused by volcanism or mass methane release. Bowring (1998) even suggests maybe all 3 occurred at once. Siberian volcanism is shown to be synchronous with the P-T extinction, and so Mundil believes it to be most likely. Succession found in quarries at South China (Meishan period) have been the source of much data used to try and explain the mass extinction event and its causes. Isotopic data combined with biomarker data both gathered from Meishan-1 core both show significant ecological disturbance and biogeochemical change that predates the fauna transition therefore marking the Permian Triassic boundary, and helping to explain why the extinction event took place. One scenario put forward by Cao (2009) used to explain the cause of the PTB event is the eruption of the Siberian flood basalts triggering oceanic and atmospheric disturbances which had a significant impact on marine fauna and other life. Black (2014) suggests these mass volcanic releases would have resulted in acid rain leading to the extinction. This theory is seen as highly sound due to the volcanic event occurring from the Siberian traps being one of the largest known volcanic events in the last 500 million years, and coinciding with the P-T extinction. PTB biomarker studies are also used as a tool in an attempt to explain the mass extinction event. Redox sensitive biomarkers suggest the presence of a superanoxic conditions during the time of the PTB event which especially affected shallow marine environments, again hinting to a cause of the PTB extinction (Cao 2009).
References
C. Cao, et al. (2009). Biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end-Permian mass extinction event. Earth and Planetary Science Letters, 281: P. 188–201.
M. Joachimski, et al. (2012). Climate warming in the latest Permian and the Permian-Triassic mass extinction. Geological Society of America. 40: p. 195-198.
S. A. Bowring, et al. (1998). U/Pb Zircon Geochronology and Tempo of the End-Permian Mass Extinction. Vol. 280, Issue 5366, pp. 1039-1045.
B. A. Black, et al. (2014). Acid rain and ozone depletion from pulsed Siberian Traps magmatism. Vol. 42, pp. 67-70.
S. Z. Shen, et al. (2011). Calibrating the End-Permian Mass Extinction. Vol. 334, Issue 6061, pp. 1367-1372.
R. Mundil, et al. (2004). Age and Timing of the Permian Mass Extinction: U/Pb Dating of Closed-system Zircons. Health Research Premium Collection. 305: (5691): P.1760 – 1762.
D. H. Erwin. (1998). The end and the beginning: recoveries from mass extinctions. Vol. 13, Issue 9, pp. 344-349.
H. Visscher, et al. (2011). Fungal virulence at the time of the end-Permian biosphere crisis? Vol. 39, Issue 9, pp. 883-886.
R. J. Twitchett. (2007). The Lilliput effect in the aftermath of the end-Permian extinction event. Vol. 252, Issue 1-2, pp. 132-144.
Photos
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