How Extinction Level Event Causes Impact Earth's Biodiversity

Extinction-level events (ELEs) are catastrophic occurrences that lead to a significant and widespread loss of biodiversity across the planet. These events can be triggered by a variety of causes, each with its own unique impact on Earth's ecosystems. Understanding these impacts is crucial for comprehending the fragility and resilience of life on Earth, and for informing strategies to mitigate current biodiversity loss (Shen, 2024).

Causes of Extinction Level Events

Extinction-level events can be triggered by a range of factors, both terrestrial and extraterrestrial. These causes often interact in complex ways, exacerbating the effects on biodiversity (Shen, 2024).

Terrestrial Causes

• Volcanic Activity: Large-scale volcanism, such as the Siberian Traps eruptions during the Permian-Triassic extinction, can release massive amounts of greenhouse gases (CO2, methane), leading to rapid global warming, ocean acidification, and anoxia (oxygen depletion) (Shen, 2024).
• Climate Change: Rapid global warming or cooling can disrupt ecosystems, exceeding the thermal limits of many species and leading to widespread mortality (Shen, 2024). Aridification, or the increase in dry climates, can also devastate terrestrial ecosystems (Shen, 2024).
• Sea Level Changes: Major sea-level fluctuations can inundate coastal habitats or expose vast areas of the seafloor, disrupting marine ecosystems and causing extinctions.
• Changes in Ocean Chemistry: Ocean acidification, caused by increased atmospheric CO2, can inhibit the ability of marine organisms to build shells and skeletons, particularly affecting reef-building organisms (Shen, 2024). Anoxia, or the depletion of oxygen in the oceans, can create 'dead zones' where most marine life cannot survive (Shen, 2024).

Extraterrestrial Causes

• Asteroid Impacts: Large asteroid impacts, such as the Chicxulub impact at the end of the Cretaceous period, can cause widespread devastation through shockwaves, tsunamis, wildfires, and a global 'impact winter' caused by dust and debris blocking sunlight (Montero-Martínez & Andrade-Velázquez, 2023).
• Gamma-Ray Bursts (GRBs): Although less likely, nearby GRBs could potentially deplete the Earth's ozone layer, increasing harmful solar radiation and causing significant biological damage (Sarkis et al., 2020).
• Supernovae: Similar to GRBs, nearby supernovae can also deplete the ozone layer, increasing UV radiation at the Earth's surface (Thomas, 2017). While not necessarily mass-extinction level, they can contribute to species turnover (Thomas, 2017).

Impacts on Biodiversity

The impacts of extinction-level events on biodiversity are profound and multifaceted, affecting both the composition and structure of ecosystems.

Loss of Species

• Mass Extinction: ELEs are characterized by a significant and rapid loss of species across various taxonomic groups. The Permian-Triassic extinction, for example, wiped out approximately 96% of marine species and 70% of terrestrial vertebrate species (Shen, 2024).
• Selective Extinction: Extinctions are not always random; certain groups may be more vulnerable due to their physiology, habitat, or trophic level. For example, species at higher trophic levels (top predators) are often more susceptible to extinction (Shen, 2024).
• Coextinction: The extinction of one species can trigger the extinction of other species that depend on it, leading to cascading effects throughout the food web (Shen, 2024).

Changes in Ecosystem Structure

• Simplification of Food Webs: Extinctions can lead to a simplification of food webs, with fewer species and trophic levels. This can make ecosystems more vulnerable to further disturbances (Shen, 2024).
• Loss of Keystone Species: The extinction of keystone species (species that play a critical role in maintaining ecosystem structure and function) can have disproportionately large impacts on the ecosystem.
• Habitat Loss and Degradation: ELEs can cause widespread habitat loss and degradation, further reducing biodiversity and hindering recovery.
• 'Lilliput Effect': Surviving lineages may experience a temporary decrease in body size (Shen, 2024).
• 'Lazarus Taxa': Some groups vanish from the fossil record, only to reappear later (Shen, 2024).

Recovery and Long-Term Effects

• Prolonged Recovery: The recovery of ecosystems after an ELE can take millions of years. The recovery from the Permian-Triassic extinction, for example, took approximately 10 million years (Shen, 2024).
• 'False Starts': The recovery process may be punctuated by 'false starts,' with simple, low-diversity communities temporarily dominating before being replaced by more complex ecosystems (Shen, 2024).
• Evolutionary Radiations: Extinctions can create opportunities for surviving lineages to diversify and fill vacant ecological niches, leading to evolutionary radiations.
• Long-Term Shifts in Ecosystem Structure: ELEs can lead to long-term shifts in ecosystem structure and function, with some ecosystems never fully recovering to their pre-extinction state.

Rate of Change

The rate at which environmental changes occur during an extinction event is a critical factor in determining its impact on biodiversity. Rapid changes can overwhelm the ability of species to adapt, leading to widespread extinctions (Shen, 2024). The Permian-Triassic extinction was characterized by rapid environmental changes, which likely contributed to its severity (Shen, 2024). Contemporary rates of environmental change, driven by human activities, are surpassing those of the PT extinction event, raising concerns about current biodiversity loss (Shen, 2024).

Relevance to Modern Biodiversity Loss

Studying past extinction events provides valuable insights into the causes and consequences of biodiversity loss, and can inform strategies to mitigate current threats. The Permian-Triassic extinction, in particular, offers a cautionary tale about the potential impacts of rapid climate change, ocean acidification, and habitat destruction (Shen, 2024). Understanding the mechanisms that drove past extinctions can help us to identify and address the factors that are currently threatening biodiversity (Salinas et al., 2024).