The background extinction rate represents the natural, ongoing pace at which species disappear from Earth’s ecosystems over vast geological timescales. This continuous process of species loss occurs due to various natural factors, distinct from major, rapid extinction events. It reflects the typical turnover of species throughout Earth’s biological and geological history and is often measured in extinctions per million species per year (E/MSY).
Understanding the Natural Rate
Species continuously evolve and go extinct as part of natural selection, where well-adapted organisms tend to survive, while less suited ones may vanish. This natural rate is influenced by various non-human factors.
Environmental shifts, such as gradual climate changes, geological events like volcanic activity or shifts in sea levels, and habitat alterations, can lead to species extinction if they cannot adapt quickly enough. Competition between species for resources or defense against predators also plays a role. Coevolutionary relationships can also cause extinctions, such as when a prey species develops defenses a predator cannot overcome. Additionally, the inherent lifespan of a species contributes to this natural rate of disappearance.
Determining the Background Rate
Scientists determine the background extinction rate primarily by examining the fossil record, which provides a historical account of life on Earth. Paleontologists and biologists analyze this record to estimate how long species typically exist from their appearance to their disappearance. This involves counting distinct species within specific geological time periods and identifying which ones went extinct, often focusing on periods between major mass extinction events.
For instance, an estimated background rate for mammals suggests one extinction every 200 years on average. Challenges in these calculations include variations in fossil quality across different periods and regions, and difficulties in distinguishing closely related species in the fossil record. Molecular clock methods, which use genetic differences to estimate divergence times, complement fossil analysis, especially for organisms with poor fossil preservation.
The Background Rate as a Baseline
The background extinction rate serves as a fundamental benchmark for understanding contemporary biodiversity loss. Scientists use this natural rate as a standard to measure and evaluate present-day extinction rates. It allows researchers to distinguish between the typical, ongoing process of species turnover and periods of accelerated species loss.
Comparing current extinction rates against this baseline helps highlight the magnitude of human-induced species loss. This comparison is important for assessing the health of ecosystems and overall biodiversity. The background rate also offers insights into long-term biodiversity patterns and evolutionary processes, providing context for current trends and informing conservation strategies.
Distinguishing from Current Extinction Rates
Current extinction rates are considerably higher than the natural background rate, underscoring a significant global biodiversity crisis. While the background rate is estimated at approximately 0.1 to 1 extinction per million species years (E/MSY), present-day rates are estimated to be 100 to 1,000 times greater. Some estimates even suggest current rates are 1,000 to 10,000 times higher than past natural rates. This acceleration in species loss began with the Industrial Revolution and has intensified, leading many scientists to suggest Earth is currently experiencing a “Sixth Mass Extinction” event.
The primary drivers of these elevated rates are human activities: habitat destruction (often through deforestation and urbanization), climate change (altering global temperatures and precipitation patterns), pollution, overexploitation of natural resources (such as excessive hunting or fishing), and the introduction of invasive species. These human-driven factors contribute to a rapid loss of biodiversity with potential long-term consequences for ecosystems and human well-being.