End-Triassic extinction event
The End-Triassic extinction event marks the boundary between the Triassic and Jurassic periods, 201.3 million years ago.[1] However, many of the extinctions occurred before then in the Upper Triassic.[2]
Overall, this was one of the major extinction events of the Phanerozoic eon. It profoundly affected life on land and in the oceans. At least half the species now known to have been living on Earth at that time became extinct. It was a series of extinctions when life was hit by volcanic events.
A whole class, the conodonts (extinct chordates);[3] 20% of all marine families; all large crurotarsans (non-dinosaurian archosaurs); some remaining therapsids; and many of the large amphibians such as the temnospondyls were wiped out.
The event emptied many ecological niches, and allowed the dinosaurs to take over the dominant roles in the Jurassic period. This event happened in less than 10,000 years, and occurred just before Pangaea started to break apart.[4]
Scientists have suggested several explanations for this event, but all have unanswered challenges:[2]
- Asteroid impact: no known impact crater has been dated to coincide with the Triassic–Jurassic boundary.
- Gradual climate change or sea-level fluctuations during the Upper Triassic. Sea level was low at the end of the Triassic, and the climate on Pangaea was arid. However, this does not explain the suddenness of the extinctions.
- Massive volcanic eruptions would release carbon dioxide, which would cause intense global warming, or sulfur dioxide and aerosols, which would cause severe cooling. The flood basalts of the Central Atlantic Magmatic Province (CAMP) occurred at the Triassic-Jurassic boundary. This is the favoured explanation of several palaeontologists.[5][6][7]
Recent evidence
A recent paper in PNAS shows fairly clearly that mass volcanism was involved. It was probably the primary cause of the extinction. Mercury is present in volcanic rocks found at the end-Triassic boundary.[8]
Mercury is emitted in gaseous form during volcanism, and deposited in sediments. The paper says "Such episodic volcanism likely perturbed the global environment over a long time and strongly delayed ecological recovery".
End-Triassic Extinction Event Media
Conodonts were a major vertebrate group which died out at the end of the Triassic
Capitosaurs (such as this Mastodonsaurus) were among the major amphibian groups which became extinct at the T-J boundary, though many may have died out earlier.
Reptile extinction at the end of the Triassic is poorly understood, but phytosaurs (such as this Redondasaurus) went from abundant to extinct by the end of the Rhaetian.
The Manicouagan reservoir in Quebec, a massive crater formed by a Late Triassic impact. Radiometric dating has determined that it is about 13 million years older than the Triassic–Jurassic boundary, and thus an unlikely candidate for a mass extinction.
Maximum extent of CAMP volcanism at the Triassic-Jurassic boundary
References
- ↑ Whiteside, Jessica H.; et al. (2010). "Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction". PNAS. 107 (15): 6721–5. Bibcode:2010PNAS..107.6721W. doi:10.1073/pnas.1001706107. PMC 2872409. PMID 20308590.
- ↑ 2.0 2.1 L.H. Tanner, S.G. Lucas & M.G. Chapman 2004. Assessing the record and causes of late Triassic extinctions. Earth-Science Reviews 65, 1-2, 103-139. [1]
- ↑ The extinction of conodonts —in terms of discrete elements— at the Triassic-Jurassic boundary
- ↑ Smith, Roff (2011-11-16). "Dark days of the Triassic: Lost world". Nature. 47 (7373): 287–289. Bibcode:2011Natur.479..287S. doi:10.1038/479287a. PMID 22094671. S2CID 34488745. Retrieved 2011-11-18.
- ↑ Benton M.J. 2003. When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson.
- ↑ Benton M.J. 2015. Vertebrate palaeontology, Blackwell 4th ed, p142. ISBN 978-1-118-40684-7.
- ↑ Erwin D.H. 2006. How life on Earth nearly ended 250 million years ago. Princeton University Press.
- ↑ Percival L.M.E. et al 2017. Mercury evidence for pulsed volcanism during the Triassic mass extinction. Proceedings of the National Academy of Sciences, online publication [2].