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Our planet has experienced several profound periods of rapid biodiversity loss throughout its long history, known as mass extinctions. These catastrophic events are typically defined by the disappearance of at least 75% of species within a geologically short timeframe. Looking back, Earth has endured five such cataclysms, with causes ranging from colossal volcanic eruptions to asteroid impacts and dramatic shifts in climate, ocean levels, or atmospheric composition. For instance, the event that wiped out the non-avian dinosaurs 66 million years ago is widely linked to an asteroid strike, while the "Great Dying" at the end of the Permian Period, the most devastating extinction (Review), was likely triggered by extensive volcanism leading to global warming and ocean acidification.
Today, scientists observe an alarming acceleration in species extinction rates, far exceeding the natural "background" rate seen throughout much of Earth's history. This current crisis, often referred to as the Holocene or Anthropocene extinction, is unique because it is overwhelmingly driven by the activities of a single species: humans. Our expanding footprint across the globe, coupled with rapid climate change, is pushing countless plant and animal species toward oblivion (Review) at an unprecedented pace.
The primary human-driven culprits include habitat destruction through deforestation, urbanization, and agricultural expansion, which converts vast swathes of land for food production. Other significant factors are pollution, the overexploitation of resources through unsustainable fishing, hunting, and logging, and the introduction of invasive species. These pressures disrupt intricate ecosystems, leading to population declines and, ultimately, the irreversible loss of species. Experts estimate that current extinction rates are hundreds to thousands of times higher than the natural rate, with millions of species now threatened, underscoring the urgency of addressing this global biodiversity crisis.