The Triassic-Jurassic Extinction marks the boundary between the Triassic and Jurassic periods, 199.6 million years ago, and is one of the largest extinctions of the Mesozoic era, deeply affecting life on Earth.
At least half of the currently known species that lived on Earth at that time became extinct. A whole class of conodonts, which constituted 20% of all marine families, disappeared, all widespread crurotarsi (non-dinosaurian archosaurs), some of the remaining therapsids and many species from the widespread group of amphibians have completely disappeared.
This event freed up ecological niches, allowing dinosaurs to dominate since the Jurassic. The Triassic extinction occurred in less than 10,000 years and occurred just before Pangea began to fall apart.
However, statistical analysis of losses among marine life at this time suggests that the decrease in diversity was associated with a decline in the rate of speciation rather than an increase in extinction.
As the reasons, several options were proposed to explain this event, but all of them do not fully explain what happened:
The gradual change in climate or ocean level fluctuations during the Late Triassic. However, this does not explain the sudden extinction of creatures in the ocean. Perhaps the climate change is associated with a change in the area of the world ocean and its depth, caused by the movement of the earth's crust. The reflection of sunlight by the water surface and an increase in climate humidity provoked the appearance of polar and alpine ice caps, which in turn led to an ice age and significant freezing of the ocean.
The fall of the asteroid, but there is no dated impact crater whose formation would coincide with the Triassic-Jurassic boundary (the collision responsible for the ring-shaped structure of Lake Manikuagan occurred 12 million years before the Triassic-Jurassic extinction).
Massive volcanic eruptions, especially the outpouring of basaltic lavas in the Central Atlantic Magmatic Province (CAMP), would release carbon dioxide or sulfur dioxide into the atmosphere, which in turn would cause severe global warming (from the first gas) or cooling (from the second gas).
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The methane hydrate gun hypothesis. Warming due to volcanism and accumulation of carbon dioxide in the atmosphere led to the release of methane from bottom clathrates. The release of methane, an even stronger greenhouse gas than CO2, has accelerated warming even more, which in turn has led to more methane release from the ocean floor. This process could lead to a rapid change in global temperature.
The isotropic structure of the Late Triassic and Early Jurassic fossilized soils does not show evidence of any change in the amount of carbon dioxide (CO2) in the atmosphere. However, later, some evidence was still found in soils belonging to the Triassic-Jurassic boundary, suggesting that there was an increase in the amount of atmospheric CO2 and some researchers have suggested that the cause of this increase and as a consequence of the mass extinction could be a combination of volcanic CO2 released from the lava, and catastrophic decomposition of gas hydrates. In addition, gas hydrates have been proposed as one of the possible causes of the massive Permian extinction at the end of the Permian.
Extinction of marine fauna during the Phanerozoic. For each time interval, it is shown what percentage of the then existing births did not survive until the next interval. The extinctions of not all genera are shown, but only those preserved in the fossils. The letters in the picture represent the “Big Five” of extinctions. 1 - Ordovician-Silurian extinction, 2 - Devonian extinction, 3 - "great" Permian extinction, 4 - Triassic-Jurassic extinction, 5 - Cretaceous-Paleogene extinction.