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Triassic-Jurassic Extinction

The Triassic-Jurassic Extinction, occurring around 201 million years ago, is one of the major mass extinction events in Earth’s history. This event marked the end of the Triassic Period and the beginning of the Jurassic Period. It had a significant impact on marine and terrestrial life, leading to changes in ecosystems and the evolution of new species.

Timing and Duration

The Triassic-Jurassic Extinction took place over a relatively short period, estimated to have occurred between 200 and 201 million years ago. This transition marks the boundary between the Triassic and Jurassic periods.

Causes and Triggers

The exact causes of the Triassic-Jurassic Extinction are still debated, but several factors are proposed to have contributed to this event:

  1. Volcanic Activity: Large-scale volcanic eruptions, such as the Central Atlantic Magmatic Province (CAMP) eruptions, are believed to have released massive amounts of volcanic gases, including carbon dioxide and sulfur dioxide. These gases could have led to climate changes, acid rain, and global environmental disturbances.
  2. Climate Change: The volcanic activity might have led to rapid and extreme climate shifts, including warming and cooling. Changes in sea level and ocean circulation patterns could have disrupted ecosystems and habitats.
  3. Ocean Anoxia: The release of volcanic gases, combined with nutrient runoff from land, could have caused widespread oceanic anoxia (low oxygen levels). Anoxic conditions can lead to mass die-offs of marine organisms.
  4. Terrestrial Anoxia: There is evidence of a reduction of oxygen in the atmosphere at this time, either as a result of the huge amount of rotting vegetation caused by the event, or some other mechanism.

Impact on Life

The Triassic-Jurassic Extinction had varying impacts on different groups of organisms. Marine life, particularly marine reptiles, bivalves, ammonites, and some conodonts, experienced declines in diversity. On land, some archosaurs (including all aetosaurs, and some crocodile-line and dinosaur-line species) faced extinctions, while others survived and eventually led to the diversification of dinosaurs in the Jurassic.

Survivors and Recovery

Despite the significant loss of biodiversity, many groups of organisms managed to survive the Triassic-Jurassic Extinction. Some groups, including certain types of marine reptiles and terrestrial reptiles, diversified in the aftermath of the event. The subsequent Jurassic Period saw the rise of new species and the development of new ecological niches.

Geological Record

The evidence of the Triassic-Jurassic Extinction is preserved in the geological record as changes in fossil assemblages, sedimentary facies, and isotopic signatures. The boundary between the Triassic and Jurassic is marked by distinct layers of sedimentary rock that contain fewer or different types of fossils compared to surrounding layers.