11.4 End-Triassic extinction

The End-Triassic extinction, occurring 201 million years ago, was a major event in Earth's history. Volcanic activity, climate change, and ocean acidification contributed to widespread biodiversity loss in both marine and terrestrial ecosystems.

This extinction reshaped life on Earth, leading to the decline of reef ecosystems and the rise of dinosaurs and mammals. Understanding its causes and consequences provides insights into the long-term impacts of mass extinctions and ecosystem recovery.

Causes of End-Triassic extinction

• The End-Triassic extinction event, which occurred approximately 201 million years ago, was one of the five major mass extinctions in Earth's history
• Multiple factors likely contributed to the extinction, including volcanic activity, climate change, ocean acidification, and methane release
• The causes of the extinction had far-reaching impacts on both marine and terrestrial ecosystems, leading to significant loss of biodiversity

Volcanic activity and eruptions

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• Extensive volcanic activity during the End-Triassic, particularly the eruption of the Central Atlantic Magmatic Province (CAMP), released large amounts of CO2 and other greenhouse gases into the atmosphere
• Volcanic emissions led to global warming, ocean acidification, and disruption of ecosystems
• Lava flows from CAMP eruptions covered vast areas of land (estimated 11 million km^2), destroying habitats and causing direct mortality of organisms
• Volcanic ash and aerosols in the atmosphere reduced solar radiation reaching Earth's surface, potentially leading to short-term cooling followed by long-term warming

Climate change and global warming

• Increased atmospheric CO2 levels from volcanic activity led to global warming during the End-Triassic period
• Global average temperatures increased by an estimated 3-4°C, with more pronounced warming at higher latitudes
• Warmer temperatures altered global weather patterns, leading to changes in precipitation and increased frequency of extreme events (droughts, floods)
• Rising temperatures caused thermal stress for many organisms, exceeding their physiological tolerances and leading to local extinctions

Ocean acidification and anoxia

• Higher atmospheric CO2 levels led to increased absorption of CO2 by the oceans, causing ocean acidification
• Lower ocean pH reduced the availability of carbonate ions, making it more difficult for calcifying organisms (corals, mollusks) to build their shells and skeletons
• Ocean acidification caused widespread decline of reef ecosystems and other carbonate-dependent communities
• Warmer oceans held less dissolved oxygen, leading to expanded oxygen minimum zones and anoxic conditions in some areas
• Anoxia caused mass mortality of marine organisms and altered biogeochemical cycles

Methane release from seafloor

• Warming of the oceans during the End-Triassic period may have destabilized methane hydrates stored in seafloor sediments
• Methane, a potent greenhouse gas, was released into the water column and atmosphere, amplifying the ongoing global warming
• Oxidation of methane in the water column consumed dissolved oxygen, exacerbating ocean anoxia
• Methane release created a positive feedback loop, further accelerating climate change and environmental deterioration

Timing of End-Triassic extinction

• The End-Triassic extinction event marks the boundary between the Triassic and Jurassic periods in the geological record
• Understanding the timing and duration of the extinction is crucial for reconstructing the sequence of events and potential causes
• The extinction event is associated with significant changes in the fossil record, geochemical signatures, and sedimentary indicators

Duration of extinction event

• The End-Triassic extinction is estimated to have lasted approximately 600,000 to 1 million years, based on radiometric dating and biostratigraphic correlations
• The main phase of extinction occurred over a shorter period, likely tens to hundreds of thousands of years, with a more prolonged recovery and restructuring of ecosystems
• The duration of the extinction event varies among different taxonomic groups and geographic regions, with some lineages experiencing more rapid declines than others

Gradual vs abrupt extinction

• The pattern of extinction during the End-Triassic event is complex, with evidence for both gradual and abrupt declines in diversity
• Some taxonomic groups, such as conodonts and bivalves, show a gradual decline in diversity leading up to the main extinction horizon
• Other groups, including ammonoids and reef-building corals, experienced abrupt and catastrophic losses at the extinction boundary
• The varying patterns of extinction suggest that different environmental stressors and thresholds affected taxa differently, with some more sensitive to gradual changes and others to sudden perturbations

Patterns of End-Triassic extinction

• The End-Triassic extinction event had differential impacts on marine and terrestrial ecosystems, as well as across latitudinal gradients
• Analyzing the patterns of extinction can provide insights into the selective pressures and environmental drivers that shaped the event
• The extinction patterns also shed light on the ecological and evolutionary consequences of the event, including the restructuring of communities and the rise of new dominant groups

Marine vs terrestrial ecosystems

• Marine ecosystems were severely affected during the End-Triassic extinction, with an estimated 70-75% of marine invertebrate species going extinct
• Reef ecosystems, which were dominated by sponges, corals, and algae, suffered a major collapse and did not fully recover until the Middle Jurassic
• In terrestrial ecosystems, the extinction was less severe but still significant, with an estimated 30-50% of tetrapod species (amphibians, reptiles) going extinct
• Plant communities experienced significant turnover, with the decline of seed ferns and the rise of conifers and other gymnosperm groups

Tropical vs polar regions

• The intensity of the End-Triassic extinction varied across latitudinal gradients, with more severe impacts in tropical and subtropical regions compared to higher latitudes
• Tropical marine ecosystems, particularly reef communities, experienced the highest rates of extinction due to their sensitivity to changes in temperature, ocean chemistry, and sea level
• In terrestrial ecosystems, the extinction was more pronounced in low-latitude regions, likely due to the combined effects of warming, drought, and habitat loss
• Higher latitude ecosystems, while still affected, showed greater resilience and faster recovery rates, possibly due to more stable environmental conditions and the presence of refugia

Selective vs random extinction

• The End-Triassic extinction event exhibited a combination of selective and random patterns of extinction across different taxonomic groups and functional roles
• Some groups, such as reef-building organisms and marine reptiles, were selectively targeted due to their sensitivity to specific environmental stressors (ocean acidification, warming)
• Other groups, such as terrestrial tetrapods, experienced more random patterns of extinction, with no clear selectivity based on body size, diet, or habitat preferences
• The selective extinction of certain functional groups (e.g., reef-builders) had cascading effects on ecosystem structure and function, leading to the collapse of associated communities

Consequences of End-Triassic extinction

• The End-Triassic extinction event had far-reaching consequences for the evolution and ecology of marine and terrestrial ecosystems
• The extinction resulted in the restructuring of communities, the decline of previously dominant groups, and the rise of new lineages that would shape the future of life on Earth
• Understanding the consequences of the extinction provides valuable insights into the long-term impacts of mass extinction events and the factors that influence ecosystem recovery and resilience

Restructuring of marine communities

• The End-Triassic extinction led to a major restructuring of marine communities, with the loss of many dominant invertebrate groups (ammonoids, bivalves, brachiopods)
• The extinction of reef-building organisms caused a collapse of reef ecosystems, which did not fully recover until the Middle Jurassic
• The post-extinction marine world was characterized by a shift towards more mobile and opportunistic taxa, such as gastropods and echinoids
• The restructuring of marine communities had cascading effects on ecosystem functions, such as nutrient cycling, primary productivity, and habitat provision

Decline of reef ecosystems

• Reef ecosystems, which were major centers of biodiversity and ecosystem services in the Triassic, suffered a severe decline during the End-Triassic extinction
• The loss of reef-building organisms (corals, sponges, algae) led to the collapse of reef structures and the associated communities that depended on them
• The decline of reefs had far-reaching impacts on marine biodiversity, as they provided critical habitats and nursery grounds for many species
• The recovery of reef ecosystems was slow and gradual, with a shift towards more resilient and opportunistic taxa (e.g., microbes, algae) in the aftermath of the extinction

Rise of dinosaurs and mammals

• The End-Triassic extinction event played a crucial role in the rise of dinosaurs and mammals, two groups that would dominate terrestrial ecosystems for millions of years
• The extinction of many large terrestrial reptiles (e.g., rauisuchians, phytosaurs) created ecological opportunities for dinosaurs to diversify and occupy new niches
• Early mammals, which were small and rare during the Triassic, survived the extinction and began to diversify in the Jurassic, laying the foundation for their later success
• The rise of dinosaurs and mammals was facilitated by their adaptations to changing environmental conditions, such as endothermy and more efficient locomotion

Recovery and diversification

• The recovery of ecosystems after the End-Triassic extinction was a gradual and prolonged process, lasting millions of years
• The pace and pattern of recovery varied among different taxonomic groups and geographic regions, with some lineages rebounding more quickly than others
• The post-extinction world was characterized by increased ecological innovation and experimentation, as surviving lineages adapted to new environmental conditions and filled vacant niches
• The recovery and diversification of life set the stage for the evolution of new ecosystems and the emergence of modern-style food webs and community structures

Evidence for End-Triassic extinction

• The evidence for the End-Triassic extinction event comes from a variety of geological and paleontological records, including the fossil record, geochemical signatures, and sedimentary indicators
• These lines of evidence provide a comprehensive picture of the timing, magnitude, and environmental context of the extinction event
• The integration of multiple proxy records allows for a more robust understanding of the causes and consequences of the extinction and its impact on the evolution of life on Earth

Fossil record and stratigraphy

• The fossil record provides direct evidence for the End-Triassic extinction, with a significant decline in the diversity and abundance of many marine and terrestrial taxa across the Triassic-Jurassic boundary
• Stratigraphic sections from around the world show a sharp decrease in fossil occurrences and a change in the composition of fossil assemblages at the extinction horizon
• The disappearance of key index fossils (e.g., conodonts, ammonoids) and the appearance of new taxa (e.g., early dinosaurs) mark the boundary between the Triassic and Jurassic periods
• High-resolution biostratigraphic correlations allow for the global synchronization of the extinction event and the reconstruction of its temporal and spatial patterns

Geochemical signatures and proxies

• Geochemical proxies, such as stable isotope ratios and trace element concentrations, provide insights into the environmental conditions and perturbations associated with the End-Triassic extinction
• Carbon isotope records show a significant negative excursion at the extinction boundary, indicating a massive release of isotopically light carbon into the atmosphere and oceans (likely from volcanic activity and methane release)
• Oxygen isotope records suggest a rapid warming event coinciding with the extinction, with estimated temperature increases of 3-4°C
• Trace element proxies (e.g., mercury, osmium) show enrichment patterns consistent with increased volcanic activity and weathering rates during the extinction interval

Sedimentary indicators of environmental change

• Sedimentary records provide evidence for significant environmental changes and ecosystem disruptions during the End-Triassic extinction
• Widespread deposition of black shales and organic-rich sediments indicates the development of anoxic conditions in marine environments, likely due to a combination of warming, stratification, and increased nutrient input
• Changes in sediment composition, such as a shift from carbonate to siliciclastic deposition, reflect the collapse of carbonate-producing ecosystems (e.g., reefs) and increased terrestrial weathering and erosion
• Sedimentary structures, such as tsunami deposits and seismites, provide evidence for the occurrence of large-scale volcanic and tectonic events that may have contributed to the extinction

Comparisons to other mass extinctions

• The End-Triassic extinction is one of the five major mass extinction events in Earth's history, along with the End-Ordovician, Late Devonian, End-Permian, and End-Cretaceous extinctions
• Comparing the causes, patterns, and consequences of these events can provide insights into the general processes and mechanisms that drive mass extinctions and the factors that influence ecosystem recovery and resilience
• Understanding the similarities and differences among mass extinctions is crucial for developing a comprehensive framework for predicting and mitigating the impacts of current and future environmental crises

Similarities vs differences

• The End-Triassic extinction shares some common features with other mass extinctions, such as the association with large-scale volcanic activity (e.g., Siberian Traps in the End-Permian, Deccan Traps in the End-Cretaceous)
• However, the specific environmental perturbations and their relative importance vary among extinction events (e.g., the role of ocean acidification in the End-Triassic vs. the impact of an asteroid in the End-Cretaceous)
• The selectivity and intensity of extinction also differ among events, with some extinctions showing greater taxonomic and ecological selectivity (e.g., the End-Permian) than others (e.g., the End-Triassic)
• The patterns of recovery and diversification following each extinction event are also variable, reflecting the unique environmental and evolutionary contexts of each time period

Causes and consequences

• Comparing the causes and consequences of different mass extinctions can help identify the common drivers and mechanisms that lead to widespread ecosystem collapse and biodiversity loss
• Volcanic activity, climate change, and ocean acidification are recurring themes in many mass extinctions, highlighting the importance of these factors in driving global-scale environmental perturbations
• The consequences of mass extinctions, such as the restructuring of communities and the rise of new dominant groups, demonstrate the long-lasting impacts of these events on the evolution and ecology of life on Earth
• Understanding the causes and consequences of past mass extinctions can inform our understanding of current and future environmental challenges, such as anthropogenic climate change and biodiversity loss

Implications for understanding extinction processes

• The study of the End-Triassic extinction and its comparison to other mass extinctions has important implications for understanding the general processes and mechanisms that govern extinction events
• Mass extinctions are complex and multi-causal phenomena, often resulting from the interplay of multiple environmental stressors and feedback loops
• The vulnerability of different taxonomic and ecological groups to extinction varies depending on their life history traits, geographic distribution, and sensitivity to specific environmental perturbations
• The recovery and diversification of life after mass extinctions are shaped by the interplay of ecological opportunities, evolutionary innovations, and contingent historical factors
• Understanding the processes and patterns of past mass extinctions can help inform conservation strategies and management decisions aimed at mitigating the impacts of current and future environmental crises on biodiversity and ecosystem function