Permian-Triassic Extinction Event Notes

PERMIAN-TRIASSIC

Permo-Triassic Mass Extinction

• Also known as:
  • Permian-Triassic Extinction Event
  • End-Permian Mass Extinction (EPME)
  • The Great Dying
  • P-T

Extinction

• Extinction happens continuously (background extinction).
• Background extinction rate: $0.1-1$ extinctions per million species per year.
• Current extinction rate: $100-1000+$ times higher than the background rate (estimates vary).

Causes of Extinction

• Major causes:
  • Habitat loss
  • Climate change
• Other contributing causes.
• Past causes of habitat loss and climate change: geological factors.
• Modern causes:
  • Overharvesting
  • Pollution
  • Invasive species

Extinction Risk

• Some species are more at-risk due to specific characteristics.
• Conversely, some species are normally less at-risk due to opposite characteristics.
• Mass extinctions disrupt the "rules" of background extinction risk.

Mass Extinction

• High amount of extinction: $30$ of species.
• Affects a broad range of habitats or ecologies.
• Global in nature.
• Occurs over a short time period/abrupt change.
• Rate is considerably higher than background rates.

Mass Extinctions

• Affects approximately $30-50$ of marine families.
• Examples:
  • End-Ordovician
  • Late Devonian
  • End-Permian (Permo-Triassic)
  • Late Triassic
  • Cretaceous-Paleogene
• Smaller extinctions can still have a global signal.

Causes of Mass Extinction

• Each mass extinction event is unique.
• Multiple interacting mechanisms.
• No single common cause for all mass extinctions.

General Causes

• Sea level drop:
  • Reduces shallow shelf photic zone habitat
• Cooling or warming:
  • Changes sea level
  • Impacts organisms adapted to climate
  • Affects ocean oxygenation
• Anoxia

General Causes (Continued)

• Flood basalts:
  • Disrupt climate (cooling from "volcanic winter" or warming from greenhouse gases).
  • Contribute to anoxia
• Impact events:
  • "Impact winter" (disrupt photosynthesis).
  • Widespread fires
  • Possibly acid rain

The Big Five Extinctions

• Includes Ordovician-Silurian (OS), Late Devonian (D), Permian-Triassic (P), Triassic-Jurassic (Tr), and Cretaceous-Paleogene (K-Pg) extinction events.
• The graph illustrates the extinction rate correlated with extent and rate of temperature change

End-Permian Extinction

• Largest mass extinction in Earth's history.
• Approximately $60$ of genera and $80$ of species extinct.
• Terminal Paleozoic mass extinction.
• End of the Middle Permian (terminal Guadalupian, ~10 million years before EPME) was a large extinction (~35% of marine genera); likely had land impact too.
• Terminal Permian: 2 pulses.
• Affected terrestrial and marine organisms.
• First of the "Big 5" to include terrestrial organisms.

P-T mass extinction losses

• Forams: 97% of genera
• Radiolarians: 99% of genera
• Cnidarians: 96% of genera
• Bryozoan: 79% of genera
• Brachiopod: 96% of genera
• Bivalve: 59% of genera
• Gastropod: 98% of genera
• Ammonoids: 97% of genera
• Crinoids: 98% of genera
• Trilobites: 100% of genera
• Eurypterids: 100% of genera
• Acanthodians: 100% of genera

Totally Extinct

• Rugose and tabulate corals (all hard corals at the time).
• Trilobites.
• Blastoid echinoderms.
• Acanthodians.
• Pelycosaur synapsids, 20 families of therapsid synapsids
• Reefs and forests disappeared temporarily.

Upper Permian vs. Early Triassic

• Reefs were destroyed.
• No burrowing.
• Corals did not return until the Middle Triassic.

Environmental Changes

• Forests and plant ecosystems destroyed
• Coal formation stops
• Red beds common across boundary

Causes and contributing factors to the Permian Extinction

• Large continent = dry interiors; increasingly arid climate.
• Evidence: fossil dunes, extensive evaporite deposits.
• Low sea level and loss of shallow marine habitat.
• Poor ocean circulation due to warming and changed currents (no cold water sink at poles).
• Widespread anoxia.
• Disrupts nutrient cycling.

Siberian Traps

• Approximately $2,000,000 km^3$ of flood basalts.
• Global cooling from ash cloud.
• Global warming from $CO_2$ release.
• Possibly burned extensive coal deposits in this area.

Ocean Warming and $CO_2$ Problems

• Trap volcanism produced massive amounts of $CO_2$.
• $CO_2$ levels in ocean increased (hypercapnia) and poisoned marine life (ocean less oxygenated, more acidic).
• Support: heavily calcified organisms suffered huge losses; likely unable to form their shells correctly.

Environmental consequences of the Siberian Traps eruptions

• SO2 emissions, CO2 emissions, thermogenic methane.
• Increased continental weathering, soil erosion, global warming, oceanic anoxia.
• Increased marine productivity, disturbed landscapes.
• Negative C-isotope excursion, positive C-isotope excursion, increased seawater $\frac{^{87}Sr}{^{86}Sr}$, faster Sr reaction rates.
• Abundant microbial growth, acid rain, siltation, eutrophication.

Methane Clathrates

• Methane is a powerful greenhouse gas.
• Significant amounts stored frozen in ice crystals on seafloor (gas hydrates).
• If oceans warm enough, it can release through melting.
• Global warming catastrophe
• New estimates of ~500-2500 PgC in gas hydrates

Synthesis of Events

• Volcanic eruptions.
• Moderate global warming.
• Methane release catastrophe.
• Abrupt global warming.
• Ocean anoxia.
• EXTINCTIONS