11.5 End-Cretaceous extinction
11 min read•august 20, 2024
The marked a pivotal moment in Earth's history. This event, occurring 66 million years ago, wiped out and many other species, dramatically altering ecosystems worldwide.
The extinction was likely caused by a massive asteroid impact, coupled with volcanic activity. These events triggered global climate change, acid rain, and widespread environmental disruption, leading to a major restructuring of life on Earth.
Causes of end-Cretaceous extinction
- The end-Cretaceous extinction, also known as the (K-Pg) extinction, was a that occurred approximately 66 million years ago
- This extinction event marked the end of the Mesozoic Era and the beginning of the Cenozoic Era, resulting in significant changes to Earth's ecosystems and the extinction of many iconic groups of organisms
Chicxulub impact crater
Top images from around the web for Chicxulub impact crater
Impacts Archives - Page 2 of 2 - Universe Today View original
Is this image relevant?
Frontiers | Shaping of the Present-Day Deep Biosphere at Chicxulub by the Impact Catastrophe ... View original
Is this image relevant?
hydrothermal system Archives - Universe Today View original
Is this image relevant?
Impacts Archives - Page 2 of 2 - Universe Today View original
Is this image relevant?
Frontiers | Shaping of the Present-Day Deep Biosphere at Chicxulub by the Impact Catastrophe ... View original
Is this image relevant?
1 of 3
Top images from around the web for Chicxulub impact crater
Impacts Archives - Page 2 of 2 - Universe Today View original
Is this image relevant?
Frontiers | Shaping of the Present-Day Deep Biosphere at Chicxulub by the Impact Catastrophe ... View original
Is this image relevant?
hydrothermal system Archives - Universe Today View original
Is this image relevant?
Impacts Archives - Page 2 of 2 - Universe Today View original
Is this image relevant?
Frontiers | Shaping of the Present-Day Deep Biosphere at Chicxulub by the Impact Catastrophe ... View original
Is this image relevant?
1 of 3
- The Chicxulub impact crater, located on the Yucatan Peninsula in Mexico, provides evidence for a massive extraterrestrial impact at the end of the Cretaceous period
- The impact of a 10-15 km diameter asteroid or comet released an estimated energy equivalent of 100 trillion tons of TNT, causing global environmental disruption
- Ejecta from the impact, including iridium and shocked quartz, can be found in K-Pg boundary clay layers worldwide (Tunguska, Vredefort Dome)
- The impact likely triggered global wildfires, tsunamis, and a period of prolonged darkness and cooling due to the injection of dust and aerosols into the atmosphere
Deccan Traps volcanism
- The Deccan Traps in India represent one of the largest volcanic features on Earth, with an estimated 1.3 million km³ of basaltic lava erupted during the end-Cretaceous period
- Volcanism from the Deccan Traps released large amounts of carbon dioxide and sulfur dioxide into the atmosphere, potentially contributing to global warming and ocean acidification
- The timing and duration of coincide with the end-Cretaceous extinction, suggesting a possible causal link (Siberian Traps, Columbia River Basalts)
- Volcanic gases and ash from the Deccan Traps could have exacerbated the environmental effects of the Chicxulub impact
Climate change and cooling
- The end-Cretaceous period experienced significant climate change, with evidence for both global warming and cooling events
- Increased volcanic activity and the release of greenhouse gases likely contributed to a period of global warming during the late Cretaceous
- The Chicxulub impact and the injection of dust and aerosols into the atmosphere caused a period of global cooling and reduced sunlight, known as an impact winter
- Rapid climate change and temperature fluctuations placed stress on ecosystems and contributed to the extinction of many temperature-sensitive species
Acid rain and ocean acidification
- The release of sulfur dioxide from the Deccan Traps volcanism and the Chicxulub impact likely led to the formation of acid rain, which acidified terrestrial and aquatic environments
- Ocean acidification occurred due to the increased absorption of atmospheric carbon dioxide, reducing the pH of seawater and affecting marine calcifiers (corals, mollusks)
- Acid rain and ocean acidification disrupted food webs and caused physiological stress for many organisms, contributing to their extinction (end-Permian extinction, modern ocean acidification)
Consequences for life
- The end-Cretaceous extinction had far-reaching consequences for life on Earth, resulting in the loss of an estimated 75% of all species
- The extinction event significantly altered the course of evolution, paving the way for the rise of new groups of organisms and the reshaping of ecosystems in the Cenozoic Era
Extinction of non-avian dinosaurs
- All non-avian dinosaurs, including iconic groups like Tyrannosaurus and Triceratops, went extinct during the end-Cretaceous extinction
- The extinction of dinosaurs ended their 160-million-year dominance of terrestrial ecosystems and opened up ecological niches for the subsequent radiation of mammals and birds
- Potential causes for the extinction of non-avian dinosaurs include the direct impact of the Chicxulub asteroid, global cooling and darkness, and the collapse of food webs (Allosaurus, Velociraptor)
Extinction of marine reptiles
- , such as mosasaurs, plesiosaurs, and ichthyosaurs, also went extinct during the end-Cretaceous extinction event
- The extinction of these large marine predators likely resulted from the disruption of marine food webs and the loss of their prey species
- Changes in ocean chemistry and temperature may have also contributed to the extinction of marine reptiles (Tylosaurus, Elasmosaurus)
Extinction of flying reptiles
- , known as pterosaurs, disappeared during the end-Cretaceous extinction
- Pterosaurs occupied various ecological niches, including aerial insectivores, piscivores, and terrestrial carnivores
- The extinction of pterosaurs may have been influenced by the loss of food sources, changes in atmospheric conditions, and competition with early birds (Pteranodon, Quetzalcoatlus)
Extinction of ammonites
- , a diverse group of cephalopod mollusks, went extinct at the end of the Cretaceous period
- Ammonites were important components of marine ecosystems, serving as both predators and prey
- The extinction of ammonites may have been caused by ocean acidification, changes in ocean circulation patterns, and the loss of planktonic food sources (Baculites, Scaphites)
Extinction of rudist bivalves
- , a group of reef-building mollusks, disappeared during the end-Cretaceous extinction event
- Rudists were important contributors to the formation of carbonate platforms and reefs in shallow marine environments
- The extinction of rudists likely resulted from the collapse of reef ecosystems due to changes in sea level, ocean chemistry, and the loss of symbiotic algae (Titanosarcolites, Hippurites)
Survival of crocodilians and turtles
- Crocodilians and turtles are among the few groups of large reptiles that survived the end-Cretaceous extinction
- The survival of these groups may be attributed to their adaptability, diverse diets, and ability to withstand environmental stress
- Crocodilians and turtles likely benefited from the extinction of other large aquatic predators, such as marine reptiles, and the availability of new ecological niches (Crocodylus, Trionyx)
Survival of mammals and birds
- Mammals and birds are two groups of vertebrates that survived and diversified after the end-Cretaceous extinction
- The extinction of non-avian dinosaurs and other dominant groups allowed mammals and birds to radiate into new ecological niches and evolve new forms
- The survival of mammals and birds may be attributed to their small size, adaptability, and ability to exploit new food sources in the post-extinction environment (Purgatorius, Archaeopteryx)
Recovery and diversification
- The recovery and diversification of life after the end-Cretaceous extinction occurred over millions of years, with the establishment of new ecosystems and the evolution of new groups of organisms
- The period, which followed the end-Cretaceous extinction, witnessed significant changes in climate, flora, and fauna that shaped the modern world
Paleocene-Eocene thermal maximum
- The (PETM) was a period of rapid global warming that occurred approximately 56 million years ago
- During the PETM, global temperatures increased by 5-8°C, and large amounts of carbon were released into the atmosphere and oceans
- The PETM led to significant changes in plant and animal communities, with the migration of warm-adapted species to higher latitudes and the evolution of new forms (Gastornis, Coryphodon)
- The PETM is considered an analog for modern anthropogenic climate change and provides insights into the potential consequences of rapid warming on ecosystems
Rise of mammals
- The extinction of non-avian dinosaurs at the end of the Cretaceous period opened up ecological niches for the diversification and rise of mammals
- Mammals underwent a rapid adaptive radiation in the early Paleogene, evolving into a wide range of forms and occupying various ecological roles
- The Paleocene and Eocene epochs saw the appearance of early primates, rodents, bats, and whales, among other mammalian groups (Plesiadapis, Ambulocetus)
- The rise of mammals laid the foundation for the evolution of modern mammalian fauna and the establishment of new terrestrial ecosystems
Avian radiation and diversification
- Birds, the only surviving lineage of dinosaurs, underwent a significant evolutionary radiation and diversification after the end-Cretaceous extinction
- The early Paleogene witnessed the appearance of many modern bird groups, including waterfowl, shorebirds, and perching birds
- Birds evolved a wide range of adaptations for flight, feeding, and reproduction, allowing them to occupy diverse ecological niches (Presbyornis, Lithornithidae)
- The diversification of birds played a crucial role in the establishment of new terrestrial and aquatic ecosystems in the Cenozoic Era
Modern rainforest origins
- The early Paleogene period saw the development and expansion of modern rainforest ecosystems, particularly in the tropics
- The warm and humid climate of the Paleocene and Eocene epochs favored the growth of angiosperm-dominated forests with high plant diversity
- The origin of modern rainforests provided new habitats and resources for the diversification of many plant and animal groups, including insects, primates, and birds (Nothofagus, Arecaceae)
- The establishment of modern rainforests had significant implications for global carbon cycling, climate regulation, and the evolution of biodiversity
Appearance of legume plants
- Legume plants, belonging to the family Fabaceae, first appeared and diversified during the early Paleogene period
- Legumes are characterized by their ability to form symbiotic relationships with nitrogen-fixing bacteria, allowing them to thrive in nutrient-poor soils
- The appearance of legumes had significant ecological and evolutionary consequences, as they played a crucial role in the nitrogen cycle and the diversification of herbivorous insects and mammals (Acacia, Mimosa)
- The spread of legume plants likely contributed to the expansion of grasslands and savannas in the later Cenozoic Era
Evidence and dating
- The end-Cretaceous extinction and its associated events are well-documented in the geological record, with evidence from various sources, including sedimentary layers, fossils, and geochemical markers
- Dating techniques, such as magnetostratigraphy and , have allowed scientists to constrain the timing and duration of the extinction event and its aftermath
Iridium anomaly at K-Pg boundary
- The K-Pg boundary clay layer, which marks the end of the Cretaceous period, is characterized by a high concentration of iridium, an element rare in Earth's crust but abundant in asteroids and comets
- The iridium anomaly was first discovered by Luis and in 1980 and provided strong evidence for an extraterrestrial impact at the end of the Cretaceous
- The global distribution of the iridium anomaly suggests that the impact had worldwide effects and was a major contributor to the end-Cretaceous extinction
- The iridium anomaly has been identified in K-Pg boundary sections worldwide, including in Italy, Denmark, and New Zealand
Shocked quartz and tektites
- Shocked quartz is a form of quartz that has undergone intense pressure and temperature changes, often associated with meteorite impacts or nuclear explosions
- The presence of shocked quartz in K-Pg boundary sediments provides evidence for the high-energy impact of the Chicxulub asteroid
- Tektites, which are small glass spherules formed from molten rock ejected during an impact, have also been found in K-Pg boundary layers (Beloc Formation, Haiti)
- The distribution and composition of shocked quartz and tektites support the for the end-Cretaceous extinction
Fossil pollen and spores
- Fossil pollen and spores from K-Pg boundary sediments provide insights into the changes in plant communities across the extinction event
- A sharp decline in the diversity and abundance of pollen and spores is observed in many K-Pg boundary sections, indicating a significant disruption of terrestrial ecosystems
- The presence of fungal spores and the dominance of fern spores in post-extinction sediments suggest a period of ecological upheaval and the proliferation of pioneering plants (Cyathidites, Laevigatosporites)
- Changes in the composition of pollen and spore assemblages reflect the extinction of many plant groups and the subsequent recovery and diversification of flora
Magnetostratigraphy and radiometric dating
- Magnetostratigraphy, which involves the study of magnetic reversals recorded in sedimentary and volcanic rocks, has been used to date and correlate K-Pg boundary sections worldwide
- The K-Pg boundary coincides with the reversal between Chron 29r and Chron 29n, providing a global time marker for the extinction event
- Radiometric dating techniques, such as 40Ar/39Ar dating of volcanic ash layers and U-Pb dating of zircons, have been used to constrain the age of the K-Pg boundary (66.0 ± 0.1 Ma)
- The combination of magnetostratigraphy and radiometric dating has allowed for the precise dating and correlation of K-Pg boundary sections and the events surrounding the end-Cretaceous extinction
Faunal turnover and extinctions
- The K-Pg boundary is marked by a significant turnover in fossil faunas, with the extinction of many iconic groups and the appearance of new lineages
- Detailed studies of fossil assemblages across the K-Pg boundary have revealed the pattern and selectivity of extinctions, with some groups (e.g., ammonites, non-avian dinosaurs) experiencing complete extinction while others (e.g., mammals, birds) survived and diversified
- The at the K-Pg boundary is characterized by the disappearance of many large-bodied vertebrates and the proliferation of smaller, more generalist forms (multituberculates, archaic ungulates)
- The patterns of extinction and survival provide insights into the ecological and evolutionary consequences of the end-Cretaceous event and the factors that influenced the selectivity of extinctions
Comparison to other extinctions
- The end-Cretaceous extinction is one of the five major mass extinctions in Earth's history, each with its own unique characteristics and potential causes
- Comparing the end-Cretaceous extinction to other mass extinctions, such as the end-Permian and end-Triassic events, can provide insights into the common factors and differences that shape these global biotic crises
End-Cretaceous vs end-Permian
- The end-Permian extinction, which occurred approximately 252 million years ago, was the most severe in Earth's history, with an estimated 95% of marine species and 70% of terrestrial vertebrate species going extinct
- The end-Permian extinction is thought to have been caused by a combination of factors, including Siberian Traps volcanism, ocean anoxia, and global warming
- While both the end-Cretaceous and end-Permian extinctions involved significant volcanic activity, the end-Permian event was characterized by a more prolonged period of volcanism and a greater magnitude of environmental change
- The recovery and diversification of life after the end-Permian extinction took longer and followed a different trajectory compared to the post-Cretaceous recovery
End-Cretaceous vs end-Triassic
- The end-Triassic extinction, which occurred approximately 201 million years ago, was another major mass extinction that shaped the evolution of life on Earth
- The end-Triassic extinction is thought to have been caused by the eruption of the Central Atlantic Magmatic Province (CAMP) and associated environmental changes, such as global warming and ocean acidification
- Both the end-Cretaceous and end-Triassic extinctions involved significant volcanic activity and led to the extinction of many marine and terrestrial groups (conodonts, crurotarsans)
- However, the end-Triassic extinction was not associated with a major impact event, and the recovery and diversification of life followed a different pattern, with the rise of dinosaurs and the evolution of modern coral reefs
Role of volcanism vs impacts
- The relative roles of volcanism and impacts in causing mass extinctions have been a topic of debate among scientists
- While the end-Cretaceous extinction is primarily attributed to the Chicxulub impact, the contribution of Deccan Traps volcanism is still being investigated
- In contrast, the end-Permian and end-Triassic extinctions are thought to have been primarily caused by massive volcanic eruptions (Siberian Traps, CAMP)
- The comparison of the end-Cretaceous extinction to other events highlights the potential for both impacts and volcanism to cause significant environmental changes and biotic crises, depending on their magnitude and timing
Selectivity and severity of extinctions
- Mass extinctions vary in their selectivity and severity, with some events causing more widespread and catastrophic losses than others
- The end-Permian extinction is considered the most severe, with a higher proportion of species and higher-level taxa going extinct compared to the end-Cretaceous event
- The selectivity of extinctions can be influenced by factors such as geographic range, body size, trophic level, and ecological specialization
- Comparing the selectivity and severity of extinctions across different events can provide insights into the factors that make certain groups more vulnerable to extinction and the potential for differential recovery and diversification
Recovery time and ecosystem restructuring
- The recovery time and the patterns of ecosystem restructuring
Key Terms to Review (23)
Ammonites: Ammonites are an extinct group of marine mollusks belonging to the class Cephalopoda, characterized by their spiral-shaped shells and complex suture patterns. These fascinating creatures flourished during the Mesozoic Era, particularly from the late Paleozoic through the end of the Cretaceous period, and they are often used as important index fossils for dating rock layers.
Background extinction rate: The background extinction rate is the average rate at which species go extinct over long periods of geological time, typically estimated to be around 1 to 5 species per million species per year. This concept provides a baseline for understanding biodiversity loss and is crucial for analyzing mass extinction events, such as those occurring at the end of significant geological periods.
Biodiversity loss: Biodiversity loss refers to the decline in the variety and variability of life forms within a given ecosystem or on Earth as a whole. This term encompasses the extinction of species, the reduction of populations, and the degradation of ecosystems, which can result from various factors such as climate change, habitat destruction, pollution, and overexploitation of resources. The impact of biodiversity loss can be profound, affecting ecological stability and resilience, and is particularly significant during mass extinction events.
Chicxulub Crater: The Chicxulub Crater is a large impact structure located on the Yucatán Peninsula in Mexico, formed approximately 66 million years ago when a massive asteroid or comet collided with Earth. This event is widely associated with the mass extinction that led to the demise of the dinosaurs and many other species at the end of the Cretaceous period, marking a significant turning point in Earth's biological history.
Cretaceous-Paleogene: The Cretaceous-Paleogene (K-Pg) boundary marks a significant geological and biological transition that occurred approximately 66 million years ago, characterized by a mass extinction event that wiped out around 75% of all species on Earth, including the non-avian dinosaurs. This boundary signifies the end of the Mesozoic Era and the beginning of the Cenozoic Era, and it is crucial for understanding the dynamics of Earth's history and the evolution of life following this catastrophic event.
Deccan Traps Volcanism: Deccan Traps volcanism refers to a series of volcanic eruptions that formed the Deccan Traps, one of the largest volcanic provinces in the world, located in western India. These massive outpourings of basaltic lava occurred around 66 million years ago and are significant in discussions about the End-Cretaceous extinction due to their potential role in environmental changes that contributed to the extinction of many species, including the dinosaurs.
Ecosystem collapse: Ecosystem collapse refers to a significant and often irreversible breakdown of ecological systems, leading to the loss of biodiversity, disruption of food webs, and the failure of ecosystem services. This term highlights how interconnected species and environmental factors can be severely impacted by dramatic changes, such as climate shifts or habitat destruction, which are often evident during mass extinction events.
End-Cretaceous extinction: The End-Cretaceous extinction, also known as the Cretaceous-Paleogene (K-Pg) extinction event, refers to a major mass extinction that occurred approximately 66 million years ago, resulting in the disappearance of about 75% of Earth's species, including the non-avian dinosaurs. This event marked the boundary between the Cretaceous and Paleogene periods and is often linked to catastrophic events such as asteroid impacts and volcanic activity that drastically altered Earth's environment.
Faunal turnover: Faunal turnover refers to the process of replacement and reorganization of animal species in an ecosystem over time, often resulting from environmental changes or mass extinction events. This concept is crucial in understanding how ecosystems recover and transform after significant disruptions, leading to shifts in biodiversity and species composition, particularly during periods like the Late Devonian and End-Cretaceous extinctions.
Flying reptiles: Flying reptiles, also known as pterosaurs, were a diverse group of winged reptiles that lived during the Mesozoic Era, distinct from dinosaurs despite coexisting with them. They are characterized by their unique adaptations for flight, such as elongated fingers that supported their wings, a lightweight skeletal structure, and various sizes and forms that allowed them to exploit different ecological niches. Their evolutionary success is evident in their wide range of species, which included small insect-eaters to large predators.
Impact hypothesis: The impact hypothesis is a scientific theory suggesting that mass extinction events can be triggered by the collision of large celestial objects, such as asteroids or comets, with Earth. This theory posits that these impacts can cause catastrophic environmental changes, leading to significant loss of biodiversity and alterations in ecosystems. The impact hypothesis is particularly significant in explaining several major extinction events throughout Earth's history.
Iridium Layer: The iridium layer is a distinct geological marker found in the rock record, characterized by a spike in iridium concentration, which is often associated with the end-Cretaceous extinction event. This layer serves as evidence of a catastrophic impact, likely from an asteroid or comet, that led to significant environmental changes and mass extinctions around 66 million years ago, affecting many species, including the dinosaurs. Its discovery has been pivotal in understanding the causes and effects of this mass extinction.
Luis Alvarez: Luis Alvarez was an American physicist and Nobel laureate known for his work in particle physics and for proposing the asteroid impact hypothesis to explain the mass extinction event at the end of the Cretaceous period. His groundbreaking research linked a specific layer of iridium-rich clay found in the geological record to the sudden disappearance of the dinosaurs and many other species, reshaping our understanding of extinction events.
Marine reptiles: Marine reptiles are a diverse group of reptiles that adapted to life in the ocean, including well-known groups such as ichthyosaurs, plesiosaurs, and mosasaurs. These creatures thrived during the Mesozoic era, particularly in the Triassic, Jurassic, and Cretaceous periods, showcasing unique adaptations that allowed them to occupy marine environments. Their existence is crucial for understanding the evolutionary history of reptiles and their response to major extinction events.
Mass extinction: Mass extinction refers to a significant and rapid decline in the biodiversity of life on Earth, characterized by the loss of a large number of species over a relatively short geological time frame. This phenomenon often reshapes ecosystems and paves the way for new species to emerge, marking important transitions in the history of life.
Mass extinction event: A mass extinction event is a significant and rapid decline in the diversity and abundance of life on Earth, resulting in the loss of a large number of species across multiple ecosystems. These events are often triggered by catastrophic environmental changes, which can include dramatic climate shifts, volcanic eruptions, or asteroid impacts. The End-Cretaceous extinction is one of the most famous examples, leading to the disappearance of the dinosaurs and many other species.
Non-avian dinosaurs: Non-avian dinosaurs are a group of reptiles that dominated terrestrial ecosystems during the Mesozoic Era, specifically from the late Triassic to the end of the Cretaceous period, around 66 million years ago. These creatures, which include well-known species like Tyrannosaurus rex and Triceratops, went extinct during a mass extinction event at the close of the Cretaceous. Their extinction marked a significant turning point in Earth's biological history, paving the way for the rise of mammals and ultimately, birds as the only surviving lineage of dinosaurs.
Paleocene-Eocene Thermal Maximum: The Paleocene-Eocene Thermal Maximum (PETM) was a significant global warming event that occurred around 56 million years ago, marked by a rapid increase in Earth's temperatures and major changes in climate and ecosystems. This period is characterized by elevated levels of greenhouse gases, particularly carbon dioxide and methane, which led to dramatic shifts in flora and fauna, highlighting the connections between climate change and extinction events.
Paleogene: The Paleogene is a geologic period that spans from about 66 to 23 million years ago, following the end of the Cretaceous period and preceding the Neogene period. It is characterized by significant evolutionary developments, particularly in mammals and birds, as they diversified after the extinction event that marked the end of the dinosaurs. This period played a crucial role in shaping modern terrestrial environments and ecosystems.
Radiometric dating: Radiometric dating is a scientific method used to determine the age of materials by measuring the radioactive decay of isotopes within them. This technique is crucial for establishing timelines in geology and paleontology, linking fossil records and geological events to specific time periods.
Rudist bivalves: Rudist bivalves are a group of extinct marine mollusks that thrived during the Late Cretaceous period, characterized by their unusual shell structures, which often formed reef-like formations. They played a crucial role in shaping marine ecosystems, especially in warm, shallow seas, and are significant for understanding the evolution of reef systems and marine biodiversity during their time.
Stratigraphy: Stratigraphy is the branch of geology that studies rock layers (strata) and layering (stratification), primarily to understand the temporal and spatial relationships of geological formations. This field provides crucial insights into the Earth's history, including fossil records, which aid in understanding the processes of fossilization and preservation, and how these layers relate to different geological time units and significant periods in Earth's history.
Walter Alvarez: Walter Alvarez is a geologist and paleontologist known for his pivotal role in developing the asteroid impact hypothesis for the mass extinction event at the end of the Cretaceous period, about 66 million years ago. His groundbreaking work, particularly the discovery of a layer of iridium-rich clay in the geological record, suggested a link between an extraterrestrial impact and the extinction of dinosaurs, changing our understanding of this catastrophic event.