According to Nate Hagens, a mass extinction refers to a relatively rapid, severe reduction in the biodiversity of Earth, during which a significant percentage of species across multiple groups—ranging from microorganisms, plants, to large animals—are wiped out. This phenomenon typically occurs over geological timescales and is marked by the simultaneous extinction of multiple lineages, disrupting ecosystems and paving the way for profound evolutionary changes. Hagens emphasizes that mass extinctions have historically been driven by cataclysmic environmental shifts, such as massive volcanic eruptions, drastic climate changes, or asteroid impacts. Today, he would argue, human activities like deforestation, climate change, pollution, and overexploitation of resources represent analogous forces, potentially precipitating a modern mass extinction event, characterized by unprecedented rates of biodiversity loss.

See also: carrying capacity, fossil fuel, climate change, great simplification, population growth