5.4 Mass extinctions and their impact on biodiversity
3 min read•july 22, 2024
Earth's history is marked by five major mass extinctions, where vast numbers of species vanished rapidly. These events, like the "" and the dinosaur-killing , reshaped life on our planet.
Mass extinctions were caused by , , and . They drastically reduced biodiversity, but also paved the way for new evolutionary paths. Today, human activities are driving a biodiversity crisis that could lead to a sixth mass extinction.
Mass Extinctions
Mass extinctions in Earth's history
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Top images from around the web for Mass extinctions in Earth's history
Charting Earth’s (Many) Mass Extinctions — Blog of the Long Now View original
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Earth's five mass extinction events View original
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- Events characterized by rapid, global decrease in biodiversity with significant proportion of species going extinct within geologically short time period
- Typically 75% or more of all species go extinct during mass extinction event
- The Big Five mass extinctions in Earth's history
- End-Ordovician (444 million years ago)
- (372 million years ago)
- End-Permian (252 million years ago)
- Most severe mass extinction, known as "The Great Dying"
- Estimated 95-96% of marine species and 70% of terrestrial vertebrate species went extinct
- (201 million years ago)
- End-Cretaceous (66 million years ago)
- Famous for extinction of non-avian dinosaurs (Tyrannosaurus rex, Triceratops)
Causes of mass extinctions
- Asteroid impacts
- Cause global cooling due to dust and aerosols blocking sunlight
- Trigger wildfires, tsunamis, and acid rain
- at End-Cretaceous boundary
- Volcanic eruptions
- Large-scale eruptions release vast amounts of ash, dust, and greenhouse gases
- Ash and dust block sunlight, causing global cooling
- Greenhouse gases lead to global warming
- eruptions at End-Permian boundary
- Large-scale eruptions release vast amounts of ash, dust, and greenhouse gases
- Climate change
- Rapid changes in temperature disrupt ecosystems (global warming or cooling)
- Changes in ocean circulation patterns affect nutrient distribution and marine life
- Global cooling during End-Ordovician extinction
Impact on biodiversity and recovery
- Mass extinctions drastically reduce global biodiversity
- Many species, including entire families or orders, go extinct (ammonites, trilobites)
- Ecosystems disrupted and food webs collapse
- Recovery after mass extinctions is gradual
- Surviving species adapt to new niches and evolve into new forms
- Biodiversity slowly increases as new species emerge
- Recovery can take millions of years
- Mass extinctions alter course of evolution
- Surviving lineages radiate and diversify, leading to new evolutionary paths
- Rise of mammals after End-Cretaceous extinction
Current biodiversity crisis
- Current biodiversity crisis characterized by rapid species loss due to human activities
- , fragmentation, and degradation (deforestation, urbanization)
- Overexploitation of resources (overfishing, poaching)
- Pollution and climate change (plastic waste, greenhouse gas emissions)
- Invasive species introduction (rats on islands, zebra mussels in lakes)
- Current extinction rates estimated to be 100 to 1,000 times higher than background extinction rate
- Background extinction rate: 1-5 species per year
- Current extinction rate: 100-1,000 species per year
- If current trends continue, Earth may experience sixth mass extinction
- Referred to as Anthropocene or Holocene extinction
- Unique in being primarily driven by human activities rather than natural causes
- Consequences of current biodiversity crisis
- Loss of ecosystem services (pollination, water filtration)
- Reduced resilience to environmental changes
- Potential cascading effects on human well-being and global economy
Key Terms to Review (22)
Adaptive radiation: Adaptive radiation is the rapid evolution of diversely adapted species from a common ancestor in response to different environmental pressures. This process allows organisms to exploit various ecological niches, leading to increased biodiversity. It is particularly significant in understanding how life can thrive in extreme conditions, recover from mass extinctions, and co-evolve with changing environments.
Asteroid impacts: Asteroid impacts refer to the collision of asteroids with a planetary body, causing significant geological and environmental changes. These events can lead to mass extinctions, reshaping biodiversity and the course of evolution on Earth. The consequences of these impacts can create widespread devastation, altering habitats and triggering a series of ecological shifts that can drastically affect living organisms.
Biodiversity loss: Biodiversity loss refers to the decline in the variety and variability of life forms on Earth, including species extinction and habitat degradation. This reduction affects ecosystems' resilience, stability, and productivity, ultimately impacting ecological balance and the services ecosystems provide to humanity. Understanding biodiversity loss is crucial for recognizing how mass extinctions have shaped biological diversity and how life continuously interacts with Earth's changing environments.
Chicxulub Impact: The Chicxulub Impact refers to a massive asteroid collision that occurred around 66 million years ago, resulting in the formation of the Chicxulub crater located on the Yucatán Peninsula in Mexico. This event is widely believed to have triggered the Cretaceous-Paleogene (K-Pg) mass extinction, which led to the dramatic decline of many species, including the non-avian dinosaurs. The impact had far-reaching effects on Earth's biodiversity and climate, reshaping life on the planet.
Climate change: Climate change refers to significant and lasting alterations in global temperatures and weather patterns over time. It often results from human activities, particularly the burning of fossil fuels, leading to an increase in greenhouse gases in the atmosphere. These changes can profoundly impact biodiversity and influence the co-evolution of life with Earth's environment, resulting in shifts in species distributions and ecosystem dynamics.
David Jablonski: David Jablonski is an influential paleontologist known for his work on mass extinctions and their effects on biodiversity. His research explores how catastrophic events have shaped the course of life on Earth, emphasizing patterns of extinction and recovery among different species. Jablonski's studies have provided significant insights into how past extinction events can inform our understanding of current biodiversity loss and conservation efforts.
Ecosystem collapse: Ecosystem collapse refers to a significant and often irreversible breakdown of the structure and function of an ecosystem, leading to the loss of biodiversity and the failure of ecological processes. This collapse can result from various factors, including human activities, climate change, and natural disasters, and it has profound impacts on the organisms that inhabit the ecosystem as well as on the services ecosystems provide to humanity.
End-cretaceous: The end-Cretaceous refers to the boundary marking the end of the Cretaceous period around 66 million years ago, known for one of the most significant mass extinctions in Earth's history. This event led to the extinction of approximately 75% of all species, including the non-avian dinosaurs, drastically altering the planet's biodiversity and ecological landscape. The end-Cretaceous is often linked to catastrophic events like asteroid impacts and volcanic activity that severely affected global climate conditions.
End-Permian: The End-Permian refers to the mass extinction event that occurred approximately 252 million years ago, marking the boundary between the Permian and Triassic periods. It is recognized as the most severe extinction event in Earth's history, resulting in the loss of about 90-96% of marine species and a significant reduction in terrestrial biodiversity. This catastrophic event drastically altered ecosystems and paved the way for new forms of life in subsequent eras.
End-Triassic: The end-Triassic refers to a major geological boundary marking the transition from the Triassic to the Jurassic period, occurring approximately 201 million years ago. This event is significant as it was associated with one of the five largest mass extinctions in Earth's history, where around 70-75% of species went extinct. The end-Triassic had profound effects on biodiversity, leading to the dominance of dinosaurs in the Jurassic and altering the course of evolution for many groups of organisms.
Fossil Stratigraphy: Fossil stratigraphy is the branch of geology that uses fossilized remains of organisms to correlate and date rock layers (strata) across different locations. By examining the distribution and succession of fossils within sedimentary rock layers, scientists can understand the chronological sequence of biological and geological events, providing insights into mass extinctions and their impact on biodiversity over time.
Great Dying: The Great Dying refers to a massive and widespread extinction event that occurred around 252 million years ago at the end of the Permian period, resulting in the loss of about 90% of marine species and 70% of terrestrial vertebrate species. This event had profound impacts on biodiversity, reshaping ecosystems and paving the way for new forms of life in the aftermath.
Habitat destruction: Habitat destruction refers to the process in which natural habitats are altered or eliminated, leading to the loss of biodiversity and the displacement of species. This phenomenon is often driven by human activities such as urban development, agriculture, deforestation, and pollution. The impact of habitat destruction is profound, as it not only threatens individual species but also disrupts entire ecosystems and the services they provide.
Index fossils: Index fossils are remains of organisms that were widespread, abundant, and existed for a relatively short geological time. They are crucial for dating and correlating the age of rock layers, particularly in the context of mass extinctions and their impact on biodiversity, as they help identify periods when certain species flourished or disappeared.
Late Devonian: The Late Devonian is a geologic period that occurred roughly 382 to 359 million years ago, marking the final phase of the Devonian period. This era is significant for its remarkable biodiversity, especially in marine life, and is well-known for the mass extinction events that profoundly impacted ecosystems and species diversity.
Natural Selection: Natural selection is a fundamental mechanism of evolution where organisms better adapted to their environment tend to survive and produce more offspring. This process drives the evolution of species by favoring traits that enhance survival and reproduction, leading to a gradual change in the population over generations. It plays a crucial role in shaping biodiversity, influencing how life emerges and transitions through different stages.
Niles Eldredge: Niles Eldredge is an American paleontologist best known for his contributions to evolutionary theory, particularly through the concept of punctuated equilibrium. This theory argues that species evolution occurs in rapid bursts interspersed with long periods of stability, challenging the traditional view of gradual evolution over time. Eldredge's work emphasizes the importance of mass extinctions and their role in shaping biodiversity.
Siberian Traps: The Siberian Traps are a large region of volcanic rock formations in Siberia, Russia, formed during one of the largest volcanic events in Earth's history around 252 million years ago. This massive outpouring of basalt lava is closely associated with the Permian-Triassic extinction event, which wiped out a significant portion of life on Earth, thus impacting biodiversity dramatically.
Species rebound: Species rebound refers to the recovery of populations and the resurgence of biodiversity following significant reductions caused by events like mass extinctions or drastic environmental changes. This phenomenon highlights the resilience of ecosystems, as many species can repopulate and adapt to changing conditions, ultimately restoring ecological balance over time.
Survival of the fittest: Survival of the fittest is a phrase that describes the mechanism of natural selection, where organisms better adapted to their environment tend to survive and produce more offspring. This concept highlights that not all individuals have equal chances of survival; those with advantageous traits are more likely to thrive, reproduce, and pass on these traits to future generations. In essence, it underscores the dynamic relationship between organisms and their environments, shaping biodiversity over time.
Triassic-Jurassic Boundary: The Triassic-Jurassic boundary marks a significant geological and biological transition that occurred around 201 million years ago, signaling the end of the Triassic period and the beginning of the Jurassic period. This boundary is notable for being associated with one of the largest mass extinctions in Earth's history, leading to dramatic shifts in biodiversity and the dominance of different groups of organisms in the subsequent Jurassic period.
Volcanic eruptions: Volcanic eruptions are geological events where magma from beneath the Earth's crust is expelled to the surface, often resulting in explosive activity that can release ash, lava, and gases. These eruptions can have profound effects on the environment, climate, and biodiversity, particularly during mass extinction events where large-scale eruptions may lead to significant atmospheric changes.