- Triassic–Jurassic extinction event
The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, Ma|Jurassic, and is one of the major
extinction events of the Phanerozoiceon, profoundly affecting life on land and in the oceans. Twenty percent of all marine families and all large crurotarsans (non-dinosaurian archosaurs), some remaining therapsids, and many of the large amphibians were wiped out. At least half of the species now known to have been living on Earth at that time went extinct. This event vacated ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassicperiod. This event happened in less than 10,000 years and occurred just before Pangaeastarted to break apart.
Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a decrease in
speciationthan by an increase in extinctions. [Citation | last=Bambach | first=R.K. | last2=Knoll | first2=A.H. | last3=Wang | first3=S.C. | title=Origination, extinction, and mass depletions of marine diversity | journal=Paleobiology | volume=30 | issue=4 | pages=522–542 | date=December 2004 | url=http://www.bioone.org/perlserv/?request=get-document&issn=0094-8373&volume=30&page=522 | doi=10.1666/0094-8373(2004)030<0522:OEAMDO>2.0.CO;2]
Several explanations for this event have been suggested, but all have unanswered challenges:
* Gradual climate change or sea-level fluctuations during the late
Triassic. However, this does not explain the suddenness of the extinctions in the marine realm.
* Asteroid impact, but no impact crater has been dated to coincide with the Triassic–Jurassic boundary.
* Massive volcanic eruptions, specifically the flood basalts of the
Central Atlantic Magmatic Province, would release carbon dioxideor sulfur dioxidewhich would cause either intense global warming (from the former) or cooling (from the latter).
The isotopic composition of fossil soils of
Late Triassicand Early Jurassicshow no evidence of any change in the CO2 composition of the atmosphere. More recently however, some evidence has been retrieved from near the Triassic–Jurassic boundary suggesting that there was a rise in atmospheric CO2 and some researchers have suggested that the cause of this rise, and of the mass extinction itself, could have been a combination of volcanic CO2 outgassing and catastrophic dissociation of gas hydrate. Gas hydrates have also been suggested as one possible cause of the largest mass extinctionof all time; the so-called "Great Dying" at the end of the PermianEra.
*cite journal|first=J. P.|last=Hodych|coauthors=G. R. Dunning|title=Did the Manicougan impact trigger end-of-Triassic mass extinction?|journal=Geology|volume=20|date=1992|pages=pp. 51.54|doi=10.1130/0091-7613(1992)020<0051:DTMITE>2.3.CO;2
*cite journal|first=J. C.|last= McElwain|coauthors=D. J. Beerling, F. I. Woodward|title=Fossil Plants and Global Warming at the Triassic-Jurassic Boundary|journal=Science|date= 27 August 1999|volume=285 (no. 5432)|pages=1386–1390
*cite journal|first=L.H.|last= Tanner|coauthors=S.G. Lucas, M.G. Chapman|title=Assessing the record and causes of Late Triassic extinctions|journal=Earth-Science Reviews|issue=65|year=2004|pages=pp.103 – 139|doi=10.1016/S0012-8252(03)00082-5|volume=65 [http://museums.state.nm.us/nmmnh/pdf_files/TJB.pdf]
*cite journal|first=L. H.|last=Tanner|coauthors=J. F. Hubert, B. P. Coffey et al|title=Stability of atmospheric CO2 levels across the Triassic/Jurassic boundary|journal=Nature|volume=411|date=7 June 2001|pages=pp. 675–677|doi=10.1038/35079548
* [http://palaeo.gly.bris.ac.uk/Palaeofiles/Triassic/triextict.htm Theories on the Triassic-Jurassic Extinction]
* [http://nai.arc.nasa.gov/impact/news_detail.cfm?ID=23&keyword=250 The Triassic-Jurassic Mass Extinction]
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