12.2 Causes and mechanisms of mass extinctions
2 min read•august 7, 2024
Mass extinctions reshape life on Earth, wiping out species and altering ecosystems. Various causes, from asteroid impacts to volcanic eruptions, can trigger these events. Understanding these mechanisms helps us grasp the fragility of life and the long-term consequences of environmental changes.
The aftermath of mass extinctions involves complex ecological shifts. Anoxic events in oceans, habitat destruction, and trophic cascades can amplify the initial die-off. Some species may survive the initial event but face "evolutionary debt," struggling to adapt to new conditions.
Extraterrestrial and Geological Causes
Asteroid Impacts and Volcanic Eruptions
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- Asteroid impacts can cause mass extinctions by releasing massive amounts of energy upon impact, triggering global wildfires, tsunamis, and blocking out sunlight with dust and debris
- at the end of the Cretaceous period (66 million years ago) is linked to the extinction of non-avian dinosaurs
- Large-scale volcanic eruptions emit vast quantities of ash, sulfur dioxide, and carbon dioxide into the atmosphere, altering global climate and causing acid rain
- eruptions at the end of the Permian period (252 million years ago) are associated with the largest known mass extinction event
Climate Change and Sea Level Fluctuations
- , such as global warming or cooling, can disrupt ecosystems and cause extinctions by altering temperature, precipitation patterns, and ocean circulation
- (PETM) around 56 million years ago saw global temperatures rise by 5-8°C, leading to extinctions and migrations
- Sea level changes can cause mass extinctions by altering the extent and distribution of marine habitats, especially in shallow continental shelf areas
- (445-444 million years ago) is linked to a rapid drop in sea level due to glaciation, reducing the available habitat for marine organisms
Oceanographic and Ecological Consequences
Anoxic Events and Habitat Destruction
- Anoxic events occur when oceans become depleted of oxygen, causing widespread die-offs of marine life
- (OAE2) during the late Cretaceous period (93-94 million years ago) is associated with the extinction of many marine species
- Habitat destruction can result from various causes, such as sea level changes, climate change, or catastrophic events, leading to the loss of species that depend on those habitats
- Destruction of reef habitats during the (201 million years ago) contributed to the decline of many marine organisms
Trophic Cascades and Evolutionary Debt
- Trophic cascades occur when the loss of key species, such as top predators or primary producers, disrupts the balance of an ecosystem, causing further extinctions down the food chain
- Decline of marine reptiles during the End-Cretaceous mass extinction likely triggered trophic cascades in marine ecosystems
- Evolutionary debt refers to the delayed extinction of species that survive the initial mass extinction event but are unable to adapt to the altered environmental conditions
- Many mammal lineages that survived the End-Cretaceous mass extinction later went extinct during the Paleocene epoch (66-56 million years ago), possibly due to evolutionary debt
Key Terms to Review (24)
Adaptive radiation: Adaptive radiation is the rapid diversification of a single ancestral lineage into a wide variety of forms, each adapted to different ecological niches. This process often occurs in response to new environmental opportunities or after mass extinction events, leading to the emergence of distinct species with unique adaptations.
Background extinction rate: The background extinction rate refers to the natural, ongoing rate at which species go extinct over long periods of time, typically measured in number of species per million species per year. This rate is a baseline against which mass extinctions can be compared, helping scientists understand the severity and impact of these larger events. It reflects the normal turnover of species due to various natural processes, including environmental changes, predation, competition, and habitat loss.
Biological recovery: Biological recovery refers to the process through which ecosystems regain their structural and functional characteristics following a disturbance, such as a mass extinction event. This recovery can involve the resurgence of species diversity, the restoration of ecological interactions, and the re-establishment of habitats. Understanding biological recovery is crucial for assessing how life on Earth rebounds after catastrophic events, including those driven by both natural phenomena and human activities.
Chicxulub Impact: The Chicxulub Impact refers to the massive asteroid collision that occurred approximately 66 million years ago near what is now the Yucatán Peninsula in Mexico. This event is widely believed to be a primary cause of the Cretaceous-Paleogene (K-Pg) mass extinction, which led to the rapid decline of nearly 75% of Earth's species, including the non-avian dinosaurs. The impact resulted in dramatic environmental changes and set off a chain reaction of ecological disruptions.
Climate Change: Climate change refers to significant and lasting alterations in temperature, precipitation, wind patterns, and other elements of the Earth's climate system over extended periods. This concept is pivotal in understanding historical ecological shifts, adaptations, and the dynamics of biodiversity across different geological epochs.
Cretaceous-paleogene extinction: The Cretaceous-Paleogene extinction event, which occurred around 66 million years ago, was a significant mass extinction that led to the disappearance of approximately 75% of Earth's species, including most dinosaurs. This event is one of the five major mass extinctions in Earth's history and is crucial for understanding the patterns and consequences of biodiversity loss over time.
David Jablonski: David Jablonski is a prominent paleobiologist known for his research on the relationship between evolution and ecology, especially concerning marine organisms and mass extinctions. His work has significantly influenced the understanding of how environmental factors shape biodiversity over time, linking biological patterns to geological processes.
Ecosystem collapse: Ecosystem collapse refers to a rapid and often irreversible breakdown of an ecosystem's structure and function, leading to significant loss of biodiversity and ecosystem services. This phenomenon can result from various stressors that overwhelm the ecological balance, causing the systems that support life to fail. Ecosystem collapse can lead to drastic changes in habitats, species extinction, and a reduction in the resilience of the environment to recover from disturbances.
End-Ordovician Mass Extinction: The End-Ordovician mass extinction was a significant global event that occurred around 445 million years ago, marking the second largest extinction event in Earth's history. This event led to the extinction of approximately 85% of marine species, largely impacting life in the oceans during the Ordovician period. It is characterized by two distinct pulses of extinction, which were likely driven by dramatic environmental changes.
End-triassic mass extinction: The end-Triassic mass extinction was a significant event that occurred around 201 million years ago, marking the boundary between the Triassic and Jurassic periods. It is characterized by the loss of approximately 76% of all species, including many marine reptiles and large amphibians, paving the way for the dominance of dinosaurs in the Jurassic period. This extinction event is often linked to several geological and climatic changes that disrupted ecosystems.
Fossil record: The fossil record is the cumulative collection of all known fossils and their placement in the geological time scale, serving as a historical archive of life on Earth. It provides crucial insights into the evolution of species, environmental changes, and past ecosystems. Understanding the fossil record allows researchers to trace the development of paleoecology as a field, examine how organisms were affected by taphonomic processes, investigate the causes of mass extinctions, and analyze the ecological and evolutionary outcomes following these events.
Habitat loss: Habitat loss refers to the process in which natural habitats are transformed, degraded, or destroyed, leading to a decline in biodiversity and the displacement of species. This phenomenon is often driven by human activities such as urbanization, agriculture, deforestation, and pollution, which fundamentally alters the environments where various organisms live. The consequences of habitat loss can significantly contribute to mass extinctions as species struggle to adapt or relocate to new areas.
Impact hypothesis: The impact hypothesis is a scientific explanation that suggests a significant extraterrestrial event, such as an asteroid or comet collision, is a primary cause of mass extinctions on Earth. This theory is particularly associated with the mass extinction event at the end of the Cretaceous period, which led to the demise of the dinosaurs and many other species. By linking these catastrophic impacts to ecological disruptions, this hypothesis sheds light on the immediate and long-term consequences that follow such mass extinctions.
Mass extinction threshold: The mass extinction threshold refers to the critical point at which the cumulative effects of environmental stressors or changes lead to a significant and rapid decline in biodiversity, resulting in the loss of a substantial proportion of species within a relatively short geological timeframe. This concept highlights how specific factors, such as climate change, habitat destruction, and biological invasions, can converge and push ecosystems beyond their resilience limits, triggering mass extinctions.
Michael Benton: Michael Benton is a prominent paleontologist known for his research on mass extinctions and vertebrate evolution. His work has significantly contributed to the understanding of the causes and mechanisms behind historical mass extinction events, particularly those that have impacted biodiversity throughout Earth's history.
Ocean acidification: Ocean acidification refers to the process by which the ocean becomes more acidic due to the absorption of excess atmospheric CO2, resulting in a decrease in pH levels. This phenomenon is closely linked to climate change, as increased carbon emissions lead to higher levels of CO2 in the atmosphere, which in turn gets absorbed by the oceans, impacting marine ecosystems and species.
Oceanic anoxic event 2: Oceanic Anoxic Event 2 (OAE 2) was a significant period in Earth's history, occurring around 94 million years ago during the Late Cretaceous, characterized by widespread anoxia in the oceans, leading to a dramatic decline in marine life. This event is linked to massive organic carbon burial and has important implications for understanding the causes and mechanisms behind mass extinctions, as it altered marine ecosystems and impacted global climate conditions.
Paleocene-Eocene Thermal Maximum: The Paleocene-Eocene Thermal Maximum (PETM) was a significant global warming event that occurred approximately 56 million years ago, marked by a rapid rise in Earth's temperatures by about 5 to 8 degrees Celsius over a relatively short geological period. This event is crucial for understanding modern climate change, the response of ecosystems to rapid temperature shifts, and the complex interactions between carbon cycles and climate dynamics.
Permian-Triassic Extinction: The Permian-Triassic extinction, also known as the Great Dying, was the most severe mass extinction event in Earth's history, occurring approximately 252 million years ago. This extinction event led to the loss of around 90-96% of marine species and 70% of terrestrial vertebrate species, drastically reshaping the planet's biodiversity. The causes and mechanisms behind this event are complex and have been linked to volcanic activity, climate change, and ocean anoxia, leading to significant ecological and evolutionary changes in its aftermath.
Sea level rise: Sea level rise refers to the increasing elevation of the ocean's surface due to various factors, including the melting of ice sheets, glaciers, and thermal expansion of seawater as it warms. This phenomenon has significant implications for coastal ecosystems and habitats, affecting both marine and terrestrial species as they adapt to changing environments. Understanding sea level rise is essential for studying the evolution and ecology of marine organisms, evaluating past mass extinction events, and informing conservation strategies for vulnerable ecosystems.
Siberian Traps: The Siberian Traps are a large geological formation of volcanic rock located in Siberia, Russia, formed during one of the largest volcanic events in Earth’s history around 250 million years ago. This massive outpouring of basaltic lava is believed to have played a significant role in the Permian-Triassic extinction event, which is the most severe extinction event known, eliminating around 90% of marine species and 70% of terrestrial vertebrate species.
Stratigraphy: Stratigraphy is the branch of geology that studies rock layers (strata) and layering (stratification). It plays a critical role in understanding the historical sequence of geological events and the age of various formations, providing vital information about past environments and biological evolution.
Trophic Cascade: A trophic cascade is a powerful ecological concept that describes how the removal or addition of a top predator in an ecosystem can drastically change the population dynamics of lower trophic levels, ultimately affecting the entire ecosystem structure. This phenomenon illustrates the interconnectedness of species and their roles in maintaining balance within their environment, highlighting how changes at one level can reverberate throughout the ecosystem.
Volcanism theory: Volcanism theory refers to the scientific understanding of volcanic activity and its processes, which are believed to significantly influence Earth's climate and ecosystems. This theory posits that large-scale volcanic eruptions can release massive amounts of gases, ash, and lava, leading to dramatic environmental changes that can contribute to mass extinctions. The impacts of volcanism are crucial in understanding the dynamics of Earth's history and how they relate to extinction events.