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Article Edited: Triassic-Jurassic Extinction Event

EDITS to page are Underlined

Written Critique:

This article does have some strong elements, while some sections of the article need to be edited. Firstly, the article contains a general clear overview, however it is very short and needs more facts and detail about the extinction to be added. For example, the duration of the extinction needs to be added, more information needs to be added about the species affected and information needs to given on the differentiation between the extinction within the marine, terrestrial and plant species. Additionally, there is no chronological flow to the article, it is very scattered. For example, it only includes two sections other than the introduction, therefore more sections such as different sections for the hypotheses need to be added to better organize the article. Moreover, the wikipedia page only discusses one of the theories in depth for the extinction of Triassic period which is volcanism, but it did not explain the others possible theories in detail such as an asteroid impact, climate change, and the change in sea level.

Furthermore, the article contains only 10 citations, however they do come from good reputable sources such as Nature and Science. Additionally, when following some of the links for the citations, they cannot be found so they need to be updated. One of these citations is the Origination, extinction, and mass depletions of marine diversity article. Likewise, one article is written in German and as such needs to be removed. Additionally, more updated articles need to be used instead of some of the dated ones. The article also includes some images which are useful and make the article more appealing, such as the image showing the ranges of families tetrapods through the Triassic and Early Jurassic. However, the image at the bottom of the article should be moved to the introduction section.  Lastly, there is no apparent bias shown in the article, which is good. Overall, this article is a good starting point when learning about the Triassic-Jurassic extinction, however much more information needs to be added about the extinction and by following the suggestions made in the critique, the article will be more polished.

Edits to Introduction:

The Triassic–Jurassic extinction event which occurred approximately 201.3 million years ago, marks the boundary between the Triassic and Jurassic periods. It lasted for an estimated duration of 40,000 to 500,000 years and is one of the major extinction events of the Phanerozoic eon, which profoundly affected life on land and in the oceans.  An estimated 76% of all marine and terrestrial species and about 20 % of all taxonomic families went extinct. Additionally, in the seas, a whole class (conodonts) and 34% of marine genera disappeared. Whereas, on land, all pseudosuchians (non-dinosaurian archosaurs) other than crocodylomorphs (Sphenosuchia and Crocodyliformes), some remaining therapsids, and many of the large amphibians became extinct. Lastly, close examinations of the Triassic–Jurassic extinction event show that the extinction was much more serious at the specific/species level than at generic and family levels.

Suggested section headings:

Section title: Hypothesized Causes of Extinction

Subheadings for diff. hypotheses:

Sea level fluctuations

Significant facies changes suggest periods of regression followed by transgression in many of the classic marine Triassic Jurassic Boundary sections in Europe Marine. Therefore, regression was thought to be a possible mechanism of biotic turnover, as a decrease in available habitat and resulting competition, would be a cause for extinction. However, many of the documented regressions have no relation to the accelerated rates of extinction. In addition, it has also been previously argued that the idea of reduced habitat during regression is flawed because lowered sea level can instead create new shallow marine habitat around oceanic islands.

Bolide impact

The possibility of an asteroid impact has been suggested for a mechanism of the extinction, however no impact crater of sufficient size has been dated to coincide with the Triassic–Jurassic boundary. It was previously thought that the Manicouagan crater located in Quebec, was the cause for the late triassic extinction, although, newer research has shown that the impact melt within the crater has a date preceding the late Triassic by about 12 million years.   Additionally, the eroded Rochechouart crater in France has most recently been dated to 201 ±2 million years ago, but at 25 km across (possibly up to 50 km across originally), appears to be too small to be the cause for the late triassic extinction. Moreover, there are many smaller impact sites that occur during the Triassic such as the, 40-km diameter Saint Martin structure in northwestern Canada (dated at 208 +/- 14 ma) and the 15-km Obolon structure in the Ukraine (dated as 215 +/- 25 Ma), but the size and dates of the impact sites do not directly overlap with the Triassic Jurassic Extinction.

CAMP Volcanism

Massive volcanic eruptions, specifically the flood basalts of the Central Atlantic Magmatic Province (CAMP), would release carbon dioxide or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter).^[9][10] The onset of magmatism is predicted to have occurred 200 million years (Ma) ago, peaking at 199.0 ± 2.4 Ma, and continuing for over 600 kyr.

However, the timing of the CAMP eruptions has not yet been proven to correlate exactly with the beginning of the end-Triassic extinctions. Only the Newark rift basin, a small section of the LIP, is shown to closely match the timing of the extinctions. Furthermore, data from radioisotopic dating of the Newark supergroup and South American basalts suggests that the CAMP eruptions were not synchronous, and occurred over different intervals possibly separated by 4-5 Ma. This increases doubt for a direct correlation between timing of a end-Triassic extinction event and a catastrophic volcanic eruption.

Subsections on Effects of Volcanism:

Greenhouse warming and ocean acidification

CO² outgassing is one of the extinction mechanisms proposed in relation to CAMP volcanism. The CAMP eruptions would have released large amounts of CO² into Earth’s atmosphere, possibly causing severe greenhouse warming and ocean acidification. CO² emission most likely occurred in pulses.The maximum CO² emission rate from CAMP magmatism has been calculated at 1.6*1011 mol/year over a period of 500kyr.

However, due to uncertainty regarding the geographic scale of CAMP, the estimated volume of CO² emissions is inconclusive. Also, CO² content in the Late-Triassic was likely quite high, in comparison to modern atmospheric levels. Thus the climatic and environmental effects of a CO² spike were possibly far weaker than assumed.

Sulfur dioxide outgassing and effects

Basaltic magma is typically rich in sulfur, and CAMP sulfur content was estimated at 460 parts/million (ppm). Volcanic SO² emissions likely caused short-term warming effects in the lower atmosphere, and possibly a cooling effect in the upper atmosphere. Sulfur aerosols may have induced a volcanic winter [link:https://en.wikipedia.org/wiki/Volcanic_winter] as they increased the opacity of the atmosphere and blocked sunlight.

Using the Laki eruptions of 1783-85 as a contemporary reference, only the immediate area of CAMP eruptions would have been affected by SO² emissions. SO² along with fluorine and chlorine, cause acidic precipitation. Acidic precipitation was likely to have had significant effects on nearby inland water systems, local terrestrial areas. On the other hand, its effects on oceans and on a global scale were possibly negligible.

Section title: Atmospheric shifts from carbon injection (re: massive carbon injection - Ruhl et al., 2011)

A massive carbon isotope excursion took place in the end-Triassic, when roughly 12,000 to 38,000 Gt of 13C depleted carbon was injected into Earth’s atmosphere. The timing of this carbon injection coincided with the onsets of CAMP magmatism and end-Triassic extinction. Carbon isotope records of n-alkanes (chain carbon compounds) from wax of terrestrial plants from the area of the former Western Tethys ocean act as evidence of the large carbon isotope excursion. Dramatic global warming may have resulted from this massive carbon injection, as well as a sped up global water cycle. Furthermore, the carbon injection would likely have caused changes in terrestrial and marine ecosystems. The release of toxic gases such as sulfur dioxide would have caused terrestrial extinctions. Ocean acidification would have led to marine extinctions.

Potential causes for the massive carbon isotope excursion include CO2 release from CAMP volcanism, shifts in sea level and temperature that led to methane release from clathrate compounds in seabeds, and thermal metamorphism of organic-rich strata from flood basalts or sill intrusions (magma between older rock layers). These three sources are possibly mutually occurring, and may have causal relationships.

Similar carbon isotope excursions took place in the end-Permian, Rhaetian, Toarcian, and Eocene, as a result of 13C-depleted methane release. There may exist similarity between the causes of the end-Permian mass extinction, and the end-Triassic extinctions.

Section title: Classification of Triassic-Jurassic Extinction (re: whether or not the ETE is a mass extinction)

It has been proposed that the Triassic Jurassic extinction may not be a mass extinction, but rather a collection of isolated events. Close examination of the fossil record shows that species such as ammonoids, bivalves, and conodonts that were thought to be severely affected by the extinction were just in decline throughout the Late Triassic. In fact, the extinctions of ammonites, brachiopods, and conodonts occurred stepwise and several separate events can be recognized, with increasing extinction rates towards the end of the Triassic. Additionally, the fossil record of the Late Triassic extinction is drawn out rather than sudden and thus, the palaeontological record does not support the idea of a single catastrophic end-Triassic extinction.

Moreover, the proposed mechanisms for the extinction are not mutually exclusive. For example, Late Triassic environmental stress from changing sea level may have been intensified potentially by one of the smaller bolide impacts, and the results of the impact may have increased the climatic effects of volcanism.  Therefore, the lack of evidence for a sudden and severe extinction precisely at the TJB appears more compatible with a scenario of multiple mechanisms operating during the Late Triassic.

Section title: Relationship Between Volcanism and Impact Events

Scientists found that both volcanism and impact events (such as asteroids and comets) have similar consequences. In both cases, harmful chemical elements and aerosols are emitted into the atmosphere. The effects include the greenhouse effect, warming, darkening of the atmosphere (which decreases UV radiation and photosynthesis), stagnation of the oceans, and anoxia. Bioproductivity decreases and food chains break up, as a result, all vital processes are disturbed, and considerable portions of the biota become extinct.

“Literature” section - citation edit

• Deenen, M.H.L.; M. Ruhl; N.R. Bonis; W. Krijgsman; W. Kuerscher; M. Reitsma; M.J. van Bergen (2010). "A new chronology for the end-Triassic mass extinction".EPSL. ← Citation inaccurate - difficult to find source

Replace with:

Deenen, M. H. L., Ruhl, M., Bonis, N. R., Krijgsman, W., Kuerschner, W. M., Reitsma, M., & van Bergen, M. J. (2010). A new chronology for the end-triassic mass extinction. Earth and Planetary Science Letters,291(1-4), 113-125. doi:10.1016/j.epsl.2010.01.003