Mass Extinctions and Doomsdays

13 November 2026 Doomsday Conference – On the Sense and Nonsense of End-of-the-World Predictions (12-13 Nov 2026)

Gáspár Jékely

Centre for Organismal Studies, Heidelberg University

@jekely@biologists.social

The Blue Anchor Fault – Somerset coast, England

  • Triassic Merica mudstone (red) and Jurassic interbedded marls and muds

The geological time scale

The five major Mass extinctions

Family-level extinctions

Extinction events and continental flood basalts

  • % extinction of marine genera over the past 460 Ma
  • all “major” and several “minor” mass extinctions coincide with continental flood basalts (CFBs)
  • four largest impact craters are shown by stars

Extinction events and crater formation

  • Impact crater-formation rate (number of craters per million years) compared with times of 12 marine-mass-extinction episodes (arrows)
  • spectral analysis of the ages of 37 craters yielded a statistically significant 25.8 ± 0.6 My cycle

Galactic vertical oscillation cycles

  • the Solar System migrates through the mid-plane of the Milky Way
  • half-period estimated at about 32 ± 3 million years
  • stars, gas and dust clouds, and potentially a thin disk of dark matter concentrated in the mid-plane
  • periodic gravi­tational perturbations of the Oort Cloud comets
  • more controversial mechanism: dark matter interacts and heats up the Earth’s core
  • (last crossing: 2 Ma)

End-Permian Mass Extinction (252 Ma)

(Part I – How to die)

  • about 95% of species disappeared
  • 252 Million years ago

End-Permian Mass Extinction (252 Mia.)

  • caused by massive vulcanic eruptions in Siberia
  • massive CO2 and methane increase
  • ca. 6 °C global warming
  • very fast extinction, less than 200,000 years, synchronous in marine and terrestrial realms
  • precisely dated with the uranium-lead dating method

End-Permian Mass Extinction (252 Mia.)

  • charcoal-rich and soot-bearing layers indicate widespread wildfires on land
  • globally anoxic oceans
  • Anoxic waters -> sulfate-reducing bacteria -> release of H2S -> H2S poisoning
  • ‘runaway greenhouse’ effect
  • catastrophic soil erosion, rapid deforestation, fungal virulence

The Paleocene–Eocene Thermal Maximum (PETM)

  • ~56 million years ago
  • massive addition of isotopically-depleted carbon to the ocean and atmosphere -> carbon isotope excursion


  • ∼2000 × gigatons of carbon in the form of methane
  • (human emissions: 40 × gigatons / year; cumulative: 1500 × gigatons)
  • extreme global greenhouse warming event
  • short duration of ~100 kyr

Ocean acidification during the PETM


  • a core photo and weight % CaCO3 content plotted versus depth across the Paleocene–Eocene boundary

Ocean acidification during the PETM


  • Bulk sediment δ13C and weight % carbonate content in south Atlantic sediments
  • rapid drop in carbonate content to <1%
  • massive sea-floor carbonate dissolution

Collapse of a freshwater ecosystem during the PETM

  • lacustrine PETM section from the Jianghan Basin, eastern China
  • negative carbon isotope excursion in organic matter
  • a rapid warming by ~11 ℃

Collapse of a freshwater ecosystem during the PETM

  • mass mortalities of terrestrial and aquatic animals
  • large numbers of fish preserved in a flattened condition on a single bedding plane
  • simultaneous die-off
  • hyperthermal-induced toxigenic cyanobacterial blooms as most probable cause

Cyanobacterial blooms

  • colonial and filamentous toxigenic cyanobacteria (left panels) and their corresponding blooms

  • chemical structures of cyanobacterial toxins (hepatotoxins, dermatotoxins, neurotoxins)

Mass extinctions – sometimes it is game over

Family-level originations

(Part II – how to survive and recover)

Transient dwarfism of soil fauna during the PETM

The Lilliput Effect

  • burrow diameters are 30-46% smaller within the PETM interval
  • smaller soil fauna co-occur with dwarf mammal taxa
  • Lilliput effect also observed in other mass extinction events

Dwarfism in horses during the PETM

  • strong dwarfind in mammals related to warming during the PETM
  • first lower molar area reduced by 30%
  • followed by a ~76% increase in body size during the recovery phase

End-Ordivician extinction and recovery (444 Ma)

  • Gigantic ice sheet on Gondwana
  • Sea level 100 m lower
  • Anoxic oceans

End-Cretaceous Mass Extinction (66 Mia.)

  • 76% of species became extinct
  • asteroid impact (to the Yucatán Peninsula)
  • formation of the Chicxulub Crater

Iridium and Osmium anomalies at the K-T boundary

  • Iridium and Osmium is rare on Earth but more abundant in asteriods
  • mass extinction correlates with iridium and osmium anomalies
  • ca. 10 km diameter asteroid
  • Chicxulub Crater

Loss of forest cover, global growth of fern fauna

  • devastation of forest habitats globally
  • worldwide fern spike in the fossil record
  • ferns are pioneer species in ecological succession
  • ‘disaster flora’

Extinction and (slow) recovery of coral reefs


brick symbols: reefs
black intervals: post-extinction reef eclipses


  • repeated global mass bleaching
  • at end-Triassic 96% of coral species became extinct
  • extended post-extinction reef eclipse (few to 10 million years)
  • the implications are bleak for the future evolution of coral reefs

Today’s CO2 concentrations are unprecedented in the last 800,000 years

  • 50% higher (424 ppm) than 800k average

The Shovel

Envoi

  • global doomsdays happened regularly in the past
  • we can map in great detail how things go wrong
  • non-linear impacts
  • toxic algae, carbonate depletion, H2S, fire, runaway effects, mass die-offs
  • reduction in body size
  • doomsdays sometimes are final (i.e. no recovery)
  • recovery via ‘disaster biotas’
  • diversification burst after doomsday (radiation of rats? dogs?)
  • corals will need a few million years…
  • still 28M good years to go until the next Galactic Doom