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The End Permian Mass Extinction Essay, Research Paper

The End Permian Mass Extinction

Outline

I. Introduction

Think of a world which existed 290 million years ago. As you look out over the terran in front of you, you 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 leave 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 geologic time scale, a million years means nothing but this time things are different. In the blink of an eye things now look vastly different. The world once again looks alien but it looks worse than before. The sky is dark. Oceans are no longer teaming with life. The stench of rotting flesh and plants hangs in the air. The ground trembles under your feet. You feel an intense heat burning you 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 paragraph is a primitive example of 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.

II. Timing of the Extinction

There are many questions regarding the timing of the extinction at the end of the Permian. One of the main questions was the even a catastrophe or gradual. There is evidence for both scenarios. Some of the evidence supports an extraterrestrial event such as a meteor. Other evidence supports the theory of the ocean and terrestrial environments slowly changing.

A. Geochemical evidence

The research done by Xu Dao-Yi and Yan Zheng (1993)gives evidence for an extraterrestrial event. They made a table which showed the distribution of carbon 13, iridium, and microspherules across the P/T (Permian and Triassic) border. The section was over a thickness of 35 cm. They found a sudden depletion in C-13 falling from a value near zero to a minimum of less than ?6% in some samples. Similar patterns of C-13 have been observed in more than five P/T sections in China. Some other scientists like Baud et al (1989) argue that what could have caused 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. Even made a mistake in the timing of their rock layers. ?If the PTB [Permian Triassic boundary] is considered a catastrophic event, a short-time hiatus should be expected and is in fact a reasonable consequence of a catastrophic event? (by Xu Dao-Yi and Yan Zheng, 1993). But what is the significance of C-13 being associated with catastrophic events? Hsu et al. (1982) said that they 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 (Xu Dao-Yi and Yan Zheng, 1993)in the layer reviled some interesting results. High Ir values only occurs 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 (Xu et al., 1989). The origin of the microspherules could be multiple. They 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 elemental in boundary clays across China suggest that there is a remote possibility that the predominantly illite boundary clay 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 TiO2 and AL2O3 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

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