The End Permian Mass Extinction

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The End Permian Mass Extinction

By: Grant Erickson

Think of a world which existed 290 million years ago. As you look out over the terrain in front of you, you would think that you are on an alien planet. You see volcanoes spewing ash and lava. Beside them is the ocean which is swarming with many different species of echinoderms, bryozoans and brachiopods. As you look down onto the sea floor you are amazed at the countless number of starfish and urchins. Some animals you can’t even describe and you have no idea even what phylum they belong to. This is a world at its height in diversity of oceanic species. Millions of wondrous species existed at this time in the ocean and most of them will never appear again in Earth’s history. In the blink of an eye things now look vastly different. The sky is dark. Oceans are no longer teaming with life. The stench of sulfur, rotting flesh, and plants hangs in the air. The ground trembles under your feet. You feel an intense heat burning your face. You look up and see one of the greatest show of force mother nature has ever shown. Whole mountains are being thrown in the air. Lava and debris are everywhere. You ask yourself, what has happened? Will life ever exist on earth again?

The above maybe what the end of the Permian period could have looked like. Marine life was devastated, with a 57% reduction in the number of families (Sepkoski, 1986) and an estimated 96% extinction at the species level (Raup, 1979). Oceanic life suffered the most but terrestrial life forms were also greatly affected. There was a 77% reduction in the number of tetrapod families (Maxwell and Benton, 1987). All major groups of oceanic organisms were affected with the crinozoans (98%), anthozoans (96%), brachiopods (80%) and bryozoans (79%) suffering the greatest extinction (McKinney, 1987). The end of the Permian and beginning of the Triassic periods marked the single greatest extinction event the world has ever faced.

There are many questions regarding the speed of the extinction at the end of the Permian. Was the event a catastrophe or gradual? There is evidence for both scenarios. Some of the evidence supports an extraterrestrial event such as a meteor hitting the earth. Other evidence supports the theory that the ocean and terrestrial environments slowly changed.

The research done by Xu Dao-Yi and Yan Zheng (1993) gives evidence for an extraterrestrial event. They studied the distribution of carbon 13, iridium, and microspherules across the P/T (Permian and Triassic) border. The section was over 35 cm thick. They found a sudden depletion in C-13 falling from a value near zero to a minimum of less than –6% in some samples. This indicates an abrupt shift of carbon isotope compositions across the P/T boundary of all marine carbonate profiles of the investigated sections in China and the turning point from positive to negative lies at the boundary itself. These results confirm the catastrophic character of the PTB (Permian Triassic boundary). Similar patterns of C-13 change have been observed in more than five P/T sections in China. Other scientists like Baud et al (1989) argue that this anomaly is the result of a depositional hiatus or erosional disconformity. Xu and Yan argue that there is no evidence for a significant hiatus and that Baud et al. (1989) even made a mistake in the timing of their rock layers. “If the PTB is considered a catastrophic event, a short-time hiatus should be expected and is in fact a reasonable consequence of a catastrophic event” (Dao-Yi and Zheng, 1993). But what is the significance of C-13 being associated with catastrophic events? Hsu et al. (1982) suggested that carbon isotope anomalies are related to microplankton productivity. We will touch again on this later in the paper. Therefore, the sudden C-13 change may indicate the exact stratigraphic position of the mass killing event at the PTB. Analysis of iridium (Dao-Yi and Zheng, 1993) in the layer showed some interesting results. High Ir values only occur in the uppermost part of the layers. This means that the layer is close to the PTB. The concentration of Ir was at least an order of magnitude higher than the background values and this is characteristic of most Upper Permian and Lower Triassic boundaries. The scientists go on to say that “the existence of a rich Ir anomaly on a global scale within the K/T boundary layers of both marine and continental facies has been interpreted as highly impressive evidence for an impact origin.” Another discovery that may serve as a marker of an event is microspherules. A variety of microspherules have been discovered in the PTB layers of the Meishan section which is located in China (Dao-Yi et al., 1989). The origin of the microspherules could be multiple. They can be created by the intense heat and pressure within the Earth’s crust or my a meteor impact. There is also evidence that volcanoes may produce microspherules. Microspherules are small circular indentations in the rocks and the most abundant elements are Si or Si-Al. Mircospherules are similar to cosmic dust. Since a large amount of microspherules occurs in a thin layer of PTB layer it can serve as another event marker.

Maxwell (1989) who got his information from Clark et al. (1986) said that

The elements in boundary clays across China suggest that there is a remote possibility that the predominantly illite boundary clay resulted from the alteration of ejecta dust from a comet impact, but the most likely source was ash from a massive volcanic eruption.

The trace elements suggested that the dust was highly acidic and the ratios of TiO and AlO are low enough to support the volcanic dust scenario (Clark et al. 1986).

There is some research which gives evidence of a gradual extinction event. Magaritz et al. (1988) reported that carbon-isotope ratios are known to shift or change at some boundaries associated with a mass extinction event. A shift can occur due to a decrease in plant production following a meteor impact or from a large decrease in sea level that reduces shelf area, exposing the shelf and its accumulated organic carbon to erosion. There are sections examined in the Alps of Italy and Austria that actually show a gradual change in the C-13 content of marine organisms across the PTB. These sections show no dramatic shifts that can be associated with a mass extinction. Thus as you can see, the findings of Clark et al. (1986) and Magaritz et al. (1988) shows geochemical evidence that the mass extinction was a gradual event and not a catastrophic extinction event.

Faunal evidence is much harder to come by and explain than geochemical evidence due to the lack of PTB boundary layers. Also marine faunal evidence is much more linear than terrestrial. This means that the marine layer was created at a much more constant rate that the terrestrial layer and thus provides us with greater amount of data to work with. Yoram Eshet et al. (1995) said that fungal evidence can be used to mark the PTB layer. It can also be used for evidence to show how the extinction event occurred. There is a sharp fungal spike in the PTB layer which is made up of Lueckisporites virkkiae, Endosporites papillatus, and Klausipollenites schaubergeri spores. Yoram Eshet et al. (1995) defined four stages across the Permian-Triassic boundary. Stage one, consisted of low abundance of spores which became increasingly abundant. At the top, the disappearance of more than 95% of the Late Permian pollen and spore taxa became apparent. Stage two contained and abundance of fungal remains and here it is defined as the “fungal spike”. Also there is quite a bit of organic detritus, composed of carbonized plant debris. Stage three and four occurred after the boundary and will not be discussed. Since this fungal evidence can be seen throughout the world it makes it highly unlikely that the increase is everywhere an artifact resulting from sedimentary processes or local conditions. Also it should be noted that the fungal spike is very thin which suggests that remains could have been missed at many PTB layers. The reason there is a large fungal spike should be obvious. Fungi are known to adapt and respond quickly to environmental stress and disturbance (Harris and Birch, 1992). During a high stress period, like an extinction event, decimation of autotrophic life occurs which creates a large pool of decaying organic matter. This is evident by the abundant plant debris seen in the fungal spike.

Marine evidence for the PTB extinction event provides us with the best and most complete evidence of the event. According to Douglas H. Erwin (1993), the world’s leading expert on the Permian crisis, marine organisms such as bivalves and gastropods suffered such a great loss that most are unfamiliar even to students of invertebrate zoology. But findings by Erik Flugel and Joachim Reinhardt (1990) contains contradictory evidence that marine life suffered in the end Permian and early Triassic. It is commonly assumed that reefs are affected more severely at major extinction events than other biotopes. Another assumption is that there is a decrease in diversity of shallow-marine organisms during the Late Permian. In analyzing the Permian-Triassic reefs they found that there was no reduction in diversity of reef organisms during the last part of the Permian. Instead, there was evidence of high, and even increasing diversity of the uppermost Permian reef communities. The argument of Erik Flugel and Joachim Reinhardt (1990) was again countered by a number of scientists. Sweet (1992) showed that strata previously assigned to the topmost Permian stage was mistaken and that the strata should have been moved lower. If Sweet’s scheme is accepted, then the mass extinction becomes an intra-Triassic event. The differences in data could be due to inadequate sampling as proposed by Sepkoski (1986). The basis for this statement is that virtually no complete late Permian sections and complete sections across the PTB layers have been found. This argument is quite weak. Sweet’s theory is based on the validity of his dating techniques. So far all dating techniques use methods which extend information of how elements and compounds behave today into the past, hoping that they behave in the same way but there is no evidence for that.

As you can see, nothing is certain in the study of the Permian-Triassic extinction event. Since there is conflicting evidence of when, what, and how the extinction event occurred, there will be will be many different theories and hypothesis on the causes of the end Permian extinction. This paper will explore a few of the possibilities.

There are many theoretical causes of the Permian mass extinction. The causes are divided up into two main groups: diversity dependent and diversity independent. Diversity dependent hypotheses are new and are not very popular with many scientists but they do make sense. Diversity-dependent factors limit population growth as population size get larger. It involves a depletion of environmental factors such as oxygen, nitrogen, and carbon dioxide. Bramlette (1965) and Tappan (1968) evolved on a scenario of nutrient reduction. In the model, landscapes where flat and thus streams were not capable of transferring nutrients to the oceans. Also a reduction of upwelling activity helped the effect. They also proposed that oxygen levels may have declined as a result of a loss of primary productivity. Tappan went on to say that heavy extinction of suspension feeders at the end of the Devonian, Permian, and Cretaceous implicated changes in primary productivity as the main cause of the extinction through accumulation of organic material in the ocean and thus starving the ocean and land of nutrients. Remember that the oceans would starve if there was no upwelling. Through this mechanism the end Permian is very gradual and it would selectively remove different species at different times. Many scientists criticize this mechanism because it would cause the oceans to be virtually sterile. Wingnall (1993) criticized this hypothesis by saying “It appears unlikely that the oxygen-deficiency was induced by high productivity for, as we have shown, organic-rich facies are only patchily developed in the Griesbachian (early Triassic).” When thought through carefully, nutrient accumulation or sequestration would have reached a peak during the development of the extensive Carboniferous coal swamps and not during the Permian period.

One very interesting hypotheses is based on biogeography. Erwin (1993) said that,

Since most species occur only within a single marine province, one of the major controls on global diversity should be the number of marine provinces. Similar communities in different areas of a single province tend to have roughly similar community composition (at least for the more abundant species). Thus the species within a nearshore sandy-bottom community will tend to recur throughout a province but will differ between provinces.

Since continents usually define marine boundaries then when continents are dispersed there will be more marine provinces and thus more diversity. Erwin goes on to say that the formation of Pangea (the great super-continent) in the late Permian times forced a reduction in sea-floor spreading.

Since the depths of the ocean basins are a function of the age of oceanic crust, a reduction in the rate of sea-floor spreading will allow the mean age of the oceanic crust to increase, increasing the size of the ocean basins. The volume of the mid-ocean ridge spreading centers will also decline. The net effect should be a regression.

Richard Leakey (1995) adds an interesting parallel.

Imagine four one-inch squares, each of which has a total edge length of four inches, giving a grand total of sixteen inches. Now bring them together as a single square of side two inches. The total edge length is now a mere eight inches, just half of the previous figure. The same thing happens with individual continents and available shallow-water habitats. The formation of Pangea therefore must have devastated species in these habitats by this mechanism alone……