The Paleo Climate Scare: Has global warming been a direct causing factor in major mass extinction events?
August 27, 2018
Extinction, KT, Permian, Ordovician, Devonian, Triassic, Cretaceous, Volcanism, Warming, Meteor, Impact, Albido.
Over the nearly 4.7 billion years of its continued existence, life has had to overcome a series of overwhelmingly difficult events that reshape the environment in which they live, leading to a rapid loss in diversity as species fail to adapt. These events, whilst few in number, have an astonishing impact on the structure and function of the earths biosphere. These are referred to as mass extinctions. It has been theorised that global warming may be a major causing factor in a large majority these mass extinction events. In an analysis of the diversity of marine genera between the Cambrian and the present day, five major mass extinction events were deduced, occurring at the endings of the Ordovician, Devonian, Permian, Triassic and Cretaceous periods of geological history. It was concluded that a common factor for all these extinctions was a major change in global climate and environment, usually caused through a major trigger event such as volcanism, albido change or extraterrestrial impact. However global warming specifically was not the sole cause of these extinctions, but rather a possible factor among many.
A mass extinction can be defined as an extinction event that results in the termination of over 75% of all living species at a particular point in geological history. This paper seeks to identify, name and find the causes of the five largest mass extinctions in geological history, and attempt to find correlations between global warming and their occurrences. This was done through the use of a database of marine phylum compiled by Dr John J. Sepkoski Jr, published in 1992, as well as a selection of expert literature on the subject of mass extinction events. It is hypothesized that global warming is one of the major causing factors of these extinction events.
Five graphs of differing types were plotted using the fossilplot tool (FossilPlot.org), using the full set of marine genera available in the database. The graphs were then analyzed, and the six worst extinction events were marked and labeled on each. The five overall worst mass extinctions identified through the combined data of the five graphs, and a table was drawn cataloging the name of the extinction event, its relative and quantitative ages, as well as any possible causes based of relevant literature.
Table 1. List of the five major mass extinction events identified in the five figures, with dates and possible causes noted.
|Mass Extinction||Quantitative Age||Relative Age||Possible Causes|
|5th Mass Extinction - End-Cretaceous||66 Ma||Late Cretaceous||Large meteor strike triggering global cooling and disrupting ecological cycles.|
|4th Mass Extinction - End-Triassic||201 Ma||Late Triassic||Volcanic activity and global warming.|
|3rd Mass Extinction - End-Permian (The Great Dying)||252 Ma||Late Permian||Anoxia, volcanism, global warming, and possible meteor strike.|
|2nd Mass Extinction - End-Devonian||375 - 360 Ma||Late Devonian||Global warming and anoxia.|
|1st Mass Extinction - End-Ordovician||450 - 440 Ma||Late Ordovician||Global cooling and lowering sea levels.|
As observed in figures 2 and 5, the end-Ordovician mass extinction appears to have occurred in two distinct stages spaced approximately 1 million years apart (Erwin, 2000), around 450-440 million years ago (Table 1). The resulting extinction resulted in the destruction of approximately 25% of all families and 60% of all genera, nearly all of which were marine groups due to the minuscule presence of terrestrial organisms (Erwin, 2000). The root cause of the first stage extinction event may have been a runaway greenhouse effect created by the warm environments that spanned the globe during the Ordovician (Bond & Grasby, 2016), leading to a decline in oxygen content in the deep ocean as vertical circulation of water began to slow with rising sea levels(Bond & Grasby, 2016). The second stage may have been triggered due to rapid cooling caused by a mass congregation of land mass near the south pole, increasing overall global albino (Erwin, 2000). This cooling is evidenced through the presence of organisms adapted to cooler climates during and after the second extinction event (Erwin, 2000).
The end-Devonian mass extinction (Table 1) occurred approximately 375 - 360 million years ago (Table 1) wiping out 57% of genera and 22% of all families (Figure 2). It is one of the most debated, due to a multitude of conflicting theories. Global warming accompanied by a rise in sea level, anoxia, as well as asteroid impacts are both discussed as possible causes for the extinction (Hallam, 1998), with the main consensus of some scientists being a possible interplay between the two (Erwin, 2000). Whatever the cause, this extinction is characterised by a phase of general global warming.
4.3. End-Permian (Great Dying)
Occurring in two pulses, and reaching its peak at around 252 million years ago (Table 1), the end-Permian mass extinction, or Great Dying, defined the end of the Paleozoic era. The event lead to the extinguishing of 95% of all marine organisms (Figure 3; Figure 4; Figure 5) and 75% of all terrestrial organisms (Instruction Booklet Appendix, 2018).
The most studied potential causes of the Permian mass extinction seem to involve a mixture of ozone depletion, global warming (Shi & Waterhouse, 2010, Figure 1 A), anoxia and codification in the oceans as well as metal poisoning (Bond & Grasby, 2016).
Global warming would have lead to anoxia in the oceans, causing widespread devastation in marine ecosystems used to higher O2 concentrations (Bond & Grasby, 2016). It is possible that the anoxification of Permian surface waters lead to the release of H2S (Hydrogen Sulfide) into the atmosphere, leading to the poisoning of terrestrial environments (Bond & Grasby, 2016). Ocean acidification during the period of the extinction has been identified through the analysis of boron isotopes in the United Arab Emirates, however studies of this nature have not been widely conducted in other areas (Bond & Grasby, 2016). The ecological impacts of anoxification and acidification can be observed in the rapid decline of Brachiopods in the interval between the second pulse in the late Permian, and the early Triassic (Shi & Waterhouse, 2010; Erwin, 2000).
Occurring approximately 201 million years ago (Table 1), the end-Triassic mass extinction was the third most ecologically disturbing mass extinction event, ranked behind the end-Cretaceous and end-Permian extinctions (Bond & Grasby, 2016; Erwin, 2000). Around 22% of all families and 53% of all genera are theorised to have been terminated during this event(Figure 5).
The extinction marked a major decline among many major shelled marine phyla (Erwin, 2000) as well as a major turnover in the diversity of terrestrial flora (Bond & Grasby, 2016). The most discussed possible causes are volcanism, extraterrestrial impact and anoxia in marine systems. The extinction also coincides with a major period of global warming of 3 - 6 °C (Shi & Waterhouse, 2010, Figure 1 A; Bond & Grabsy, 2016), and the subsequent loss of many shelly marine fauna, as well as a major decline in coral diversity (Bond & Grasby, 2016). This indicates the occurrence of acidification in marine environments, caused by a spike in CO2 levels associated with a disruption in the carbon cycle (Bond & Grasby, 2016), destroying existing mineralised structures and impeding the formation of new ones. This disruption, along with acidification and global warming, are probable indicators of major volcanic activity. Layers of extremely deformed strata observed in the British isles also provide evidence for a major geological upheaval indicating volcanic seismic activity, possibly causing an earthquake of exceptionally large magnitude, or by a meteorite impact (Bond & Grasby, 2016).
4.5. End-Cretaceous (KT)
The end-Cretaceous mass extinction, sometimes referred to as the KT event, occurred around 66 million years ago (Table 1). The extinction impacted all trophic levels in the oceans (Bond & Grasby, 2016), extending from large marine reptiles to plankton. This extinction has the most well known theory of causation in the form of a deviating asteroid impact, that would have caused major disruptions in the earths various cycles, resulting in the destruction of many major ecosystems.
The extinction coincides with a large spike in iridium, an element most commonly found in extraterrestrial objects (Erwin, 2000; Bond & Grasby, 2016; Hallam, 1998). A 200km wide impact creator located in New Mexico has been dated to around the approximate time-frame of the extinction, providing further credence to the impact theory (Erwin, 2000). Such an impact would have produced an extremely large cloud of sulfur dioxide and water vapour, increasing the earths albido and resulting in cooling for an extended period of time, as well as resulting in the production of acid rain (Erwin, 2000 ). Shocked quartz, another indicator of extraterrestrial impact, and other chemical anomalies have also been observed in late-Cretaceous rock (Hallam, 1998).
According to Hallam, A (1998) the most likely causes of major environmental disruptions (global climate change, anoxia, changes in sea level and bolide impact) fall into line with the observed changes presented in the record of each extinction event. It can generally be inferred that a rapid change in climate conditions will occur during a mass extinction event, making habitats unsuitable where they were previously inhabitable.
Despite the massive amount of evidence provided from other research, the data gathered through fossilplot only covers data relating to marine genera classified circa 1992. The database compiled is considered an outdated source when looking for details below general trends, as many species have been reclassified and/or more information has been gathered on their distribution in the fossil record. The limitation to marine species also makes it impossible to interpolate the effects of the extinction on terrestrial organisms, obscuring many potential clues as to the impacts of a changing climate during each mass extinction.
From evidence gathered through Fossilplot charts and external literature, it can be determined that all the major mass extinctions coincide with major upheavals in the earths climate and carbon cycles, with various triggers, such as excessive volcanism (in the case of the Permian and Triassic), extraterrestrial impacts (as with the Cretaceous and possibly the Devonian, Permian and Triassic) and changes in the Earths albido (as with the Ordovician). These upheavals were, however, not directly correlated with global warming exclusively, but with a general pattern of major warming or cooling, either triggering the extinction or being a result of the initial trigger.
It should be noted that this study is based on data from an outdated source and limited to the analysts of marine genera.
Assesment Instruction Booklet Appendix, 2018, Deakin University.
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Erwin, D. H., 2000. Mass extinctions, notable examples of. In Levin, S. (ed.) Encyclopedia of Biodiversity, Academic Press, 111-122.
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Hallam, A. 1998, Mass extinctions in Phanerozoic time.
Shi, G.R. and Waterhouse, J.B., 2010. Late Palaeozoic global changes affecting high-latitude environments and biotas: An introduction. Palaeogeography, Palaeoclimatology, Palaeoecology 298, 1-16.