Imagine going back 290 million years to a world that seems like an unknown planet when you look at the scenery in front of you.
In its peak of diversity, the earth presents a stunning sight of volcanoes erupting ash and lava, alongside a wide range of echinoderms, bryozoans, and brachiopods prospering in the ocean. The underwater realm is teeming with plentiful starfish and urchins, as well as mysterious creatures from unidentified phyla. In summary, this world is thriving with an immense number of species residing in the deep sea.
Countless extraordinary species once thrived in the ocean, many of which will never reemerge in the history of our planet. In terms of the geological time scale, a million years holds little significance. However, the present moment showcases an immense transformation within the blink of an eye. Our world now appears alien once more, but its condition is even more dire than previous eras.
The paragraph presents a grim image of the sky being dark, the oceans devoid of life, and a strong smell of decaying flesh and plants filling the air. The ground shakes, and the heat is intense against your face. When you look up, you witness nature’s power as mountains are thrown into the air, accompanied by lava and scattered debris. This leaves us wondering what caused this destruction and if life will ever return to Earth. This description provides a simplified representation of how the end of the Permian period might have appeared. Scientific evidence indicates that during this time, marine life suffered greatly with a considerable 57% reduction in recorded families (Sepkoski, 1986) and an estimated extinction rate of 96% at the species level (Raup, 1979).
Maxwell and Benton (1987) state that the Permian-Triassic extinction event had a severe impact on both oceanic and terrestrial life. The number of tetrapod families decreased by 77%. McKinney (1987) observed significant declines in various major oceanic organism groups: crinozoans decreased by 98%, anthozoans by 96%, brachiopods by 80%, and bryozoans by 79%. This extinction event, which occurred at the boundary between the Permian and Triassic periods, is considered the most catastrophic in history. However, there are uncertainties regarding its precise timing.
One of the main questions regarding the event at hand is whether it was a catastrophe or a gradual process. There is evidence supporting both scenarios. Some evidence suggests an extraterrestrial event such as a meteor, while other evidence supports the idea of gradual changes in the ocean and terrestrial environments. A study conducted by Xu Dao-Yi and Yan Zheng (1993) provides geochemical evidence for an extraterrestrial event. They created a table showing the distribution of carbon 13, iridium, and microspherules along the P/T (Permian and Triassic) border. This section of the research spanned a thickness of 35 cm.
The C-13 levels have experienced a sudden decrease, going from nearly zero to below -6% in specific samples. This occurrence has been observed in various parts of China. Baud et al (1989) and other researchers suggest that this abnormality could be due to either a deposition gap or erosion disconformity. However, Xu and Yan dispute this argument by asserting that there is no evidence supporting a significant gap. They also highlight an error made by Baud et al regarding the timing of their rock layers. According to Xu Dao-Yi and Yan Zheng (1993), if the PTB Permian Triassic boundary is considered a catastrophic event, it would be reasonable to expect a brief pause as a consequence.
There are doubts about the importance of the relationship between C-13 and catastrophic events. Hsu et al. (1982) suggested a connection between carbon isotope anomalies and microplankton productivity, which will be further examined later in this document. Consequently, the abrupt alteration in C-13 levels could potentially indicate the precise stratigraphic location of the mass extinction event at the PTB. It is worth mentioning that interesting findings were uncovered by studying iridium (Xu Dao-Yi and Yan Zheng, 1993) within this particular layer.
The presence of elevated Ir values is limited to the uppermost layer, suggesting proximity to the PTB. Ir concentration is significantly higher than normal levels, a common feature at Upper Permian and Lower Triassic boundaries. This notable Ir anomaly found globally in both marine and continental facies at the K/T boundary layers is considered compelling evidence for an impact origin.
Microspherules, small circular indentations in rocks, have been discovered in the PTB layers of the Meishan section (Xu et al., 1989). These microspherules, which are predominantly composed of Si or Si-Al, are similar to cosmic dust and could have multiple origins. It has been suggested that the predominantly illite boundary clay in China, which contains a large amount of microspherules in a thin layer of PTB layer, may have resulted from the alteration of ejecta dust from a comet impact or from ash from a massive volcanic eruption (Maxwell, 1989; Clark et al., 1986). The proportions of trace elements in the dust indicate high acidity and low ratios of TiO2 and Al2O3, supporting the volcanic dust scenario (Clark et al., 1986).
Furthermore, research by Magaritz et al. (1988) indicates that carbon-isotope ratios can shift or change at boundaries associated with mass extinction events. This shift can be caused by a decrease in plant production following a meteor impact or a large decrease in sea level that exposes and erodes accumulated organic carbon on the shelf area.
The Alps of Italy and Austria have sections that reveal a gradual change in the C-13 content of marine organisms during the PTB. These sections do not indicate any sudden shifts linked to a mass extinction event. Thus, the findings of Clark et al. (1985) and Magaritz et al. (1988) demonstrate geochemical evidence supporting the idea that the mass extinction was a gradual rather than a catastrophic event. However, obtaining faunal evidence is more challenging because of significant gaps in the PTB boundary layers. Additionally, marine faunal evidence is more straightforward compared to terrestrial evidence. Yoram Eshet et al. (1995) suggest that fungal evidence can serve as a marker for the PTB layer.
The PTB layer displays a distinct fungal spike, characterized by high concentrations of Lueckisporites virkkiae, Endosporites papillatus, and Klausipollenites schaubergeri spores. Yoram Eshet et al. (1995) established four stages during the Permian-Triassic boundary. Initially, spore abundances were low but gradually increased. Towards the top, there was a significant decline in Late Permian pollen and spore taxa, with over 95% disappearing. The second stage exhibited abundant fungal remains, referred to as the “fungal spike.” Additionally, an ample amount of organic detritus, consisting of carbonized plant debris, was present.
Later in this paper, the description of stage three and four will be provided. It is highly improbable that the increase in fungal evidence is solely due to sedimentary processes or local conditions, because this evidence is found worldwide. It is also worth mentioning that the thinness of the fungal spike indicates that remains could have been overlooked at numerous PTB layers. The reason for the presence of a significant fungal spike should be apparent.
Fungi have the ability to quickly adapt and respond to environmental stress and disturbance (Harris and Birch, 1992). During a period of high stress, such as an extinction event, autotrophic life is heavily reduced, resulting in a substantial amount of decaying organic matter. This is evident by the abundant presence of plant debris in the fungal spike. The PTB extinction event is particularly impactful in marine environments. According to Douglas H. Erwin (1993), a renowned expert on the Permian crisis, marine organisms like bivalves and gastropods experienced the greatest impact, to the extent that they may be unfamiliar even to scholars of invertebrate zoology.
According to Erik Flugel and Joachim Reinhardt (1990), there are contradictory findings on whether marine life was affected during the end Permian and early Triassic. It is commonly believed that reefs suffer more during major extinction events compared to other habitats. Additionally, it is assumed that there was a decrease in diversity of shallow-marine organisms in the Late Permian. However, when the Permian-Triassic reefs were analyzed using advanced equipment, Flugel and Reinhardt found no reduction in the diversity of reef organisms towards the end of the Permian. In fact, they discovered evidence of high and possibly increasing diversity among the topmost Permian reef communities. Despite their argument, a number of scientists have challenged Flugel and Reinhardt’s findings.
Sweet (1992) discovered an error in the stratification of the topmost Permian stage, suggesting that it should have been placed lower. Accepting Sweet’s findings would reclassify the mass extinction as an event within the Triassic period. Sepkoski (1986) proposed that the discrepancies in data could be attributed to insufficient sampling. This is supported by the lack of complete late Permian sections and complete sections across the PTB layers.
Despite the presence of conflicting evidence, the study of the Permian-Triassic extinction event lacks fool-proof conclusions. With differing views on the timing, factors, and mechanisms of the event, numerous theories and hypotheses exist regarding its causes. This paper will explore several possibilities. One widely accepted explanation, put forth by Newell (1963), suggests diversity-dependent factors played a significant role in the end Permian extinction. Theoretical causes of the Permian mass extinction can be categorized into two main groups: diversity-dependent and diversity-independent. While diversity-dependent hypotheses are relatively new and not widely embraced, they offer compelling explanations when examined closely.
Diversity-dependent factors impose limits on population growth as the population grows larger. These factors lead to a depletion of environmental elements like oxygen, nitrogen, and carbon dioxide. Bramlette (1965) and Tappan (1968) put forward a scenario involving a decrease in nutrient availability. The model presented landscapes that were flat, resulting in streams unable to transport nutrients to the oceans. Additionally, a decline in upwelling activity exacerbated the effects. The researchers also suggested that oxygen levels may have decreased due to a reduction in primary productivity. Tappan further proposed that the significant extinction of suspension feeders during the Devonian, Permian, and Cretaceous periods indicated changes in primary productivity as the primary cause of the extinctions. This was attributed to the accumulation of organic material in the ocean, ultimately leading to nutrient deprivation in both marine and terrestrial ecosystems. It should be emphasized once more that the oceans would suffer if there was no upwelling. Through this process, the end Permian extinction occurred gradually and selectively eliminated different species at different times. However, some scientists criticize this mechanism as it would render the oceans virtually devoid of life.
Wingnall (1993) criticized this hypothesis by stating, “It seems unlikely that the oxygen-deficiency was caused by high productivity because, as we have demonstrated, areas with high organic content are only sporadically distributed in the Griesbachian early Triassic.” After careful consideration, it becomes clear that nutrient accumulation or sequestration would have peaked during the extensive development of Carboniferous coal swamps rather than the Permian period. One intriguing hypothesis is based on biogeography. Erwin (1993) suggested that the number of marine provinces serves as a major influence on global diversity since most species are confined to a single province. Similar communities within a single province tend to exhibit similar composition (at least for the more abundant species). Thus, species within a nearshore sandy-bottom community are likely to be found throughout a province but differ between provinces. As continents typically define marine boundaries, dispersal of continents leads to more marine provinces and consequently greater diversity.
Erwin explains that the formation of Pangea, the super-continent, during the late Permian period resulted in a reduction in ocean floor spreading. This reduction caused an increase in the average age of the oceanic crust and expansion of ocean basins. Additionally, mid-ocean ridge spreading centers experienced decreased volume. These factors ultimately lead to regression.
Richard Leakey (1995) makes a similar observation. He suggests visualizing four squares measuring one inch each, which have a combined total edge length of sixteen inches. However, when these squares are combined to form a single square with a side length of two inches, the total edge length decreases to only eight inches or half of the previous figure. The same principle applies to individual continents and their available shallow-water habitats.
The formation of Pangea caused devastating effects on species in these habitats through regression, increasing the continent’s surface area and altering climate patterns. This led to an increase in seasonality in nearshore waters and nutrient competition as provinces merged. As a result, global diversity reached its lowest point during the existence of the supercontinent. The continental climates and higher seasonality increased the instability of nutrients, primary productivity, and other trophic resources, impacting seasonal species the most. Meanwhile, species with broad trophic and environmental tolerances were favored. Given the complexity of studying instability, it is important to approach these hypotheses with caution.
In conclusion, a combination of factors, including the ones mentioned earlier, likely contributed to the greatest extinction event on Earth (Erwin, 1993). Moving on from diversity-dependent factors, diversity-independent hypotheses are more widely accepted. These models affect all individuals of a species equally and do not rely on the number of species present. Most extinctions fall into this category. One popular explanation for the Permian extinction is extraterrestrial phenomena. There is substantial evidence supporting this theory. In an article from Science News (1993), Monastersky discusses the discoveries made by a Canadian team studying well-preserved shales and cherts from northeastern British Columbia. These rocks formed in an inland basin and provide valuable information about an ancient ocean during the Permian period. By isolating small amounts of kerogen, which is the decomposed residue of Permian plankton, the researchers gained insights into the Permian time.
The kerogen records at the PTB show a significant decrease in the ratio of heavy C-13 atoms to light C-12 atoms. This shift in carbon isotopes is interpreted by researchers by taking advantage of the tendency of plants to avoid Carbon 13 during photosynthesis. Although plants typically incorporate some carbon-13 due to competition with other phytoplankton for carbon-12, a sudden die-off of most phytoplankton would allow survivors to have greater access to carbon-12. As these survivors sink to the ocean floor and become part of sedimentary rocks, they decrease the ratio of carbon-13 to carbon-12 within the rocks. Similarly, geochemists studying inorganic carbon from ancient plankton shells have observed abrupt drops in the carbon isotopic ratio at the end of the Permian. However, due to various factors that can influence this ratio, they have been unable to determine the exact cause of this change.
The carbon isotopic ratio in kerogen is impacted by fewer processes, offering strong support for the theory of a biological crisis in the surface ocean. As Monastersky (1993) suggests, this finding aligns with the possibility of a catastrophic event such as an asteroid. Another paper by Richard Monasterky (1997) provides additional evidence. In the Southern Hemisphere, scientist Gregory J. Retallack discovered “shocked” quartz at two sites in Antarctica and one site in Australia. This type of quartz forms solely during impacts and contains intersecting fracture sets. Additionally, the presence of iridium further contributes to the evidence. It is now known that the Cretaceous-Tertiary boundary extinction was triggered by an impact, and an increased amount of iridium is found at this boundary. Therefore, if an increase in iridium above background levels is observed at the PTB, it would indicate evidence of an impact.
The discovery of an increase in iridium and microspherules at the PTB boundary, as found by Xu Dao-Yi et al. (1993, 1985, 1989), provides empirical evidence suggesting an impact occurred. However, there are several issues with the impact theory. Firstly, evidence shows that the Permian extinction began gradually and experienced a more rapid pulse towards the end (Monastersky, 1993). Additionally, some scientists argue that the quartz crystals studied by Retallack were not shocked, as he only observed them under a light microscope, making it difficult to differentiate shock features from deformations caused by normal tectonic stress in the Earth’s crust.
According to Monastersky (1997), evidence of an impact that could cause significant losses should have been scattered around the world. Western geologists have tried to confirm the Chinese reports of iridium, but their efforts have been unsuccessful. Anomalies can lead to a concentration of iridium in a particular location, which is what the Chinese researchers have discovered (Erwin, 1993).
The hypothesis that a decrease in salinity caused the extinction of marine life was first proposed by Beurlen in 1956 (Maxwell, 1989). The main evidence for this theory was based on observations of stenohaline groups such as bryozoans, ostracodes, and corals, which were significantly reduced during the PTB event. The groups least affected by this phenomenon were gastropods and freshwater fishes.
Organisms with some tolerance of salinity variations survived and proliferated in the early Triassic. It was found that a selective extinction of marine families occurred in the BTB. Beurlen proposed that salinity progressively decreased during the second half of the Permian and reached critically low values at the PTB, persisting into the early Triassic. Early marine faunas are sparse and many previously diverse groups are absent at the PTB. Beurlen attributed this to a few places in the world where normal salinities were maintained. A global return to normal salinities would allow surviving species to repopulate the seas and appear again in the fossil record after their temporary absence. This raises the question: what caused such a large reduction in ocean salinity? Maxwell (1989) provides some answers based on the work of many scientists. In the 1950’s and 60’s, it was believed that the drop in salinity resulted from significant evaporite sedimentation, along with the formation of large quantities of dense brine that accumulated deep on the sea floor.
Reducing salinity to a safe drinking level of 30 parts per thousand would result in the massive deposition of anhydrite, gypsum, salt, and halite on the sea floor. Beurlen (1956) estimated that approximately 5*10^14 tonnes would need to be stored. However, other scientists argued that this amount would only represent 15% of the total evaporites that should be stored.
Scientists have postulated a figure of 200,000 cubic kilometers for Permian evaporite deposits. However, some scientists argue that this estimate only accounts for 10% of the actual amount. This challenges the idea that these deposits alone can explain the decrease in salinity levels. Among various explanations, Fisher (1963) proposed the brine-reflux hypothesis, suggesting that the evaporation of seawater and deposition of salts created dense brines that sank to the ocean floor. As a result, the surface water became relatively salt-free. Upon careful examination, it becomes apparent that Fisher’s hypothesis contradicts scientists who attribute the extinction to a temperature decrease.
According to Erwin (1993), a temperature decrease would result in less evaporation and potentially make the oceans saltier as fresh water becomes stored in glaciers. In fact, Bowen, a scientist in 1968, argued that Permian climates caused a 20% increase in Permian salinity compared to current levels. Bowen’s study was based on the analysis of significant Louann salt deposits from the Gulf Coast and other Paleozoic evaporites. Therefore, there remains considerable uncertainty regarding the relationship between salinity and the PTB extinction.
Erwin criticizes all of the hypotheses related to salinity. These hypotheses about salinity serve as examples of how explanations are often not true explanations. Stenohaline taxa are mostly stebotopic and it is necessary to provide additional evidence that salinity changes were the selective factor. In contrast to what some papers suggest, nautiloids did not suffer greatly during the extinction event. Blastoids and crinoids disappeared long before ammonoiads or brachiopods. “Strophomenid” brachiopods faced a much higher extinction rate compared to spiriferid brachiopods. In conclusion, none of these observations support the salinity hypothesis.
Species Area effects
If you examine the geological column, you will notice a correlation between marine regressions and major mass extinctions. However, the actual connection remains unclear.
The information provided by Erwin serves as a solid foundation for drawing various new conclusions. His ideas are rooted in the theory of island biogeography proposed by MacArthur and Wilson. According to this theory, the diversity of species on an island is influenced by the rate at which species immigrate from a mainland source, as well as the rate of extinction on the island, primarily caused by competition. As a result, the rate of immigration is expected to decrease as the number of species on the island increases, eventually approaching zero once all species from the source pool have reached the island. Similarly, as the diversity of species on the island increases, competition for resources intensifies and therefore the rate of extinction also rises.
The equilibrium species diversity will occur when the immigration rate matches the extinction rate, according to Erwin (1993). This theory suggests that smaller and more distant islands would have fewer species compared to larger islands or those closer to the source area. By applying the species-area hypothesis, we can derive a few conclusions. It is already known that during the PTB, there was a decrease in sea level and the formation of a single continent. This resulted in a reduced shelf area, limiting the habitat available for species and leading to increased competition for resources. Consequently, some species would die off, resulting in lower species diversity. Certain scientists argue that the decrease in shelf area alone could have caused the extinction.
Despite the fact that most land organisms have a connection to the sea, it is possible to speculate that there would be a decrease in the number of species on land. Numerous scientists, as reported by Erwin, have dismissed the species-area hypothesis. They base their rejection on various facts. For instance, during the Middle Eocene, there was a 50% decrease in shelf area along the Gulf Coast. The species area hypothesis would suggest a reduction in species diversity, but evidence contradicts this.
Some argue that the change in the number of marine provinces is the only factor that affects diversity. However, it seems logical to assume that if there is a reduction in species area, there should also be a reduction in the size of each marine province or at least the amount of inhabitable space within each province. Erwin (1993) presents some challenging suggestions, pointing out that if the species-area relationship is valid, regressions should have a greater impact on continents than on islands because, in general, the area of an island will increase during a regression. Modern tropical reef biotas are incredibly diverse and can rival or even surpass the tremendous diversity found in tropical rainforests. If most marine families have representatives on oceanic islands, they will be relatively protected from extinction caused by regressions.
There is strong evidence linking volcanism to the PTB extinction. A paper by Paul R. Renne et al (1995) brings together multiple studies to support this thesis. The evidence for a bolide impact and for volcanism occurred within a few hundred years of each other.
(2004) and Fisher et al. (2018) support the theory that the Siberian traps were formed by extensive volcanic activity. The massive amounts of lava and volcanic gases released during this period could have had severe consequences on Earth’s environment and potentially caused mass extinctions. The volcanic eruptions would have created a dust cloud, causing reduced photosynthesis and global cooling. Additionally, the injection of large quantities of carbon dioxide and sulfates into the atmosphere would have contributed to global warming. The conversion of sulfates to sulfuric acid would have resulted in acid rain and a reduction in the protective ozone layer. Moreover, the volcanic activity could have caused a thermal anomaly and released poisonous trace elements into the atmosphere and oceans. Therefore, due to the significant evidence for volcanism and its potential to produce similar effects as an asteroid collision, more scientists lean towards the volcanism theory as the cause of mass extinctions rather than an asteroid impact (Erwin, 1993; Rene et al., 1995; Wingnall et al., 2004; Fisher et al., 2018).The texts written by Dao-Yi et al (1993, 1989, 1995), and Erwin (1993) provide undeniable proof of volcanism in addition to the papers they referenced in their work.
Therefore, scientific evidence confirms the occurrence of a significant volcanic event during the Permian-Triassic boundary (PTB). However, the question remains as to how the Siberian volcanoes could have caused such an unprecedented global extinction. Wignall (1993) proposes a hypothesis on this matter, suggesting that the release of massive amounts of carbon dioxide during the eruption of the Siberian flood basalts may have caused global warming. This, in turn, led to the formation of extensive areas of warm saline bottom waters with low oxygen levels. The significant drop in carbon isotopes in the early Griesbachian period may be attributed to this significant input of isotopically light carbon resulting from volcanic activity. Renne (1995) provides his interpretation, suggesting that the Siberian flood volcanism, potentially combined with sulfates originating from evaporites on the Siberian platform, could have generated enough stratospheric sulfate aerosols to cause rapid global cooling. The subsequent accumulation of ice caps likely led to a dramatic marine regression and exposed the continental shelves to the air.
The widespread anomalies in C, S, and Sr isotopes can be attributed to this effect. The contribution of mantle-derived carbon dioxide and sulfur dioxide with isotopically light C and S also leads to negative anomalies in C-13 and S-34. The observed enrichments of O-18 in seawater at the boundary could have been caused by ice storage effects and increased erosion of the continental crust. The abrupt cessation of Siberian volcanism and subsequent ice cap recession would result in a rapid transgression after the boundary. The recovery of climate could have been facilitated by the slower development of greenhouse effects from volcanogenic gases, particularly carbon dioxide. This combination of a short-lived volcanic winter followed by greenhouse conditions would fully account for the extreme environmental changes that caused the P-T mass extinctions. Other factors such as pyroclastic eruptions, flood basalts, and trace element poisoning have also been proposed to explain the Permian extinction.Below, I will outline some of the most fascinating anomalies in evolution. After the extinction event took place, the aftermath yielded intriguing outcomes. Although we run the risk of overwhelming our readers with these anomalies, we cannot ignore an article that begins with the following statement: “Through an analysis of the fossil record, we have discovered some unexpected patterns in the origin of major evolutionary innovations. These patterns likely depict the workings of distinct mechanisms.” One of the most captivating “unexpected patterns” observed is the stark asymmetry between the proliferation of life during the Cambrian explosion approximately 440 million years ago and that which followed after the devastating end Permian extinction just over 200 million years ago.
Both the Cambrian explosion and the Permian extinction were characterized by intense biological innovation on a planet with limited biological diversity. The Cambrian explosion gave rise to all existing and many extinct phyla, while no new phyla emerged after the Permian extinction. Evolutionists question why this burst of invention has not been replicated since. Some attribute the asymmetry to the difference in available “adaptive space” between the two periods. At the start of the Cambrian, multicellular organisms were just beginning to evolve, resulting in almost empty adaptive space. In contrast, after the Permian extinction, the surviving species represented a diverse group with multiple adaptations.
Scientists agree that the communication of the available “adaptive space” to the “mechanism” responsible for innovation is not addressed. However, they also believe that microevolution, which is said to lead to the emergence of new species, is unable to accomplish the larger feat of macroevolution, specifically the formation of new phyla during the start of the Cambrian period (Lewin, Roger; “A Lopsided Look at Evolution,” Science, 241:201, 1988).
