Future diversity and lifespan of metazoans under global warming and oxygen depletion

Abstract. The diversification of metazoans, from cnidarians to vertebrates, began approximately 700–500 million years ago and has been shaped by dynamic environmental changes. Recurrent climate fluctuations – driven by large-scale volcanism, meteorite impacts – have caused major shifts in biodiversity. Understanding these historical patterns provides a critical foundation for projecting future biodiversity trends amid ongoing and future climate change. Building on these insights, this study integrates additional environmental drivers – including icehouse and greenhouse states, solar luminosity – induced warming, gradual declines in atmospheric carbon dioxide and oxygen, plant-related crises, and anthropogenic influences – to model future metazoan diversity across ecosystems. The results suggest that metazoans will undergo complete extinction approximately 700 million years from now – 300 to 400 million years earlier than previously estimated. Over the next 400 million years, biodiversity is projected to fluctuate through cycles of mass extinction and recovery. Beyond this, increasing solar luminosity is expected to raise peak global temperatures at ~300-million-year intervals, while declining oxygen and carbon dioxide levels will impose increasing physiological stress. These gradual changes will drive a progressive loss of biodiversity, even in the absence of distinct extinction events. Ultimately, a final extinction – likely triggered by large-scale volcanism or a meteorite impact – will eradicate all remaining metazoans. The total lifespan of metazoans on Earth is thus projected to be approximately 1.4 billion years, representing about 12 % of Earth's anticipated 12-billion-year lifespan. Humanity currently occupies the midpoint (~50 %) of this evolutionary timespan.