Table 1: The ‘Big Five’ mass extinction events

From: Has the Earth’s sixth mass extinction already arrived?

EventProposed causes
The Ordovician event64,65,66 ended 443 Myr ago; within 3.3 to 1.9 Myr 57% of genera were lost, an estimated 86% of species.Onset of alternating glacial and interglacial episodes; repeated marine transgressions and regressions. Uplift and weathering of the Appalachians affecting atmospheric and ocean chemistry. Sequestration of CO2.
The Devonian event4,64,67,68,69,70 ended 359 Myr ago; within 29 to 2 Myr 35% of genera were lost, an estimated 75% of species.Global cooling (followed by global warming), possibly tied to the diversification of land plants, with associated weathering, paedogenesis, and the drawdown of global CO2. Evidence for widespread deep-water anoxia and the spread of anoxic waters by transgressions. Timing and importance of bolide impacts still debated.
The Permian event54,71,72,73 ended 251 Myr ago; within 2.8 Myr to 160 Kyr 56% of genera were lost, an estimated 96% of species.Siberian volcanism. Global warming. Spread of deep marine anoxic waters. Elevated H2S and CO2 concentrations in both marine and terrestrial realms. Ocean acidification. Evidence for a bolide impact still debated.
The Triassic event74,75 ended 200 Myr ago; within 8.3 Myr to 600 Kyr 47% of genera were lost, an estimated 80% of species.Activity in the Central Atlantic Magmatic Province (CAMP) thought to have elevated atmospheric CO2 levels, which increased global temperatures and led to a calcification crisis in the world oceans.
The Cretaceous event58,59,60,76,77,78,79 ended 65 Myr ago; within 2.5 Myr to less than a year 40% of genera were lost, an estimated 76% of species.A bolide impact in the Yucatán is thought to have led to a global cataclysm and caused rapid cooling. Preceding the impact, biota may have been declining owing to a variety of causes: Deccan volcanism contemporaneous with global warming; tectonic uplift altering biogeography and accelerating erosion, potentially contributing to ocean eutrophication and anoxic episodes. CO2 spike just before extinction, drop during extinction.
  1. Myr, million years. Kyr, thousand years.