End–Triassic extinction event
The End–Triassic extinction event marks the boundary between the Triassic and Jurassic periods, 199.6 million years ago. However, many of the extinctions occurred before then in the Upper Triassic.
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 of the species now known to have been living on Earth at that time went extinct.
A whole class (conodonts: extinct chordates), 20% of all marine families and all large crurotarsans (non-dinosaurian archosaurs), some remaining therapsids, and many of the large amphibians were wiped out.
The event emptied many ecological niches, and allowed the dinosaurs to assume 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.
Several explanations for this event have been suggested, but all have unanswered challenges:
- 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 or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter). The flood basalts of the Central Atlantic Magmatic Province (CAMP) occurred at the Tr/J boundary.
References[change | edit source]
- Some sources give a date 201.4 mya. 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. doi:10.1073/pnas.1001706107. PMC 2872409. PMID 20308590. http://www.pnas.org/content/early/2010/03/15/1001706107.
- 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. 
- 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. doi:10.1038/479287a. http://www.nature.com/news/dark-days-of-the-triassic-lost-world-1.9375. Retrieved 2011-11-18.