GEOL 102 UNLV Lecture 19 - Mass Extinction at the End of Permian

Ediacaran Biota biodiversity:

first appearance of animals

Cambrian Explosion biodiversity:

small shelly fossils, Chenjiang, and Burgess Shale biotas

Biodiversity Through Time

• Edicaran Biota

• Cambrian Explosion

• Paleozoic Plateau

• Mesozoic-Cenozoic Radiation

• Mass Extinctions

When were the big 5 mass extinctions?

• late ordovician

• late devonian

• late permian

• late triassic

• late cretaceous

The Late Ordovician Mass Extinction:

• 26% families and 60% genera went extinct

• trilobites, corals, brachiopods, etc. hit hard

• probable cause: global cooling (glaciation)

The F/F (late Devonian) Mass Extinction

• last about 20 mi. yrs.

• 22% families and 50 genera went extinct

• marine life hit

  • reefs, brachiopods, rugose corals, marine fishes

• probable causes: ecological crisis by land plants?

How was the F/F extinction caused by land plants?

• land plants increase weathering rates

• enhanced weathering increases nutrients

• increased nutrients causes algal blooms in ocean

• bacteria decomposition of dead algae used up oxygen in ocean

• lack of oxygen led to mass extinction

The P/T (Permian-Triassic) Extinction

• < 1 Mi. yrs.

• insects, terrestrial vertebrates, marine taxa (benthic) went extinct

• Probably causes:

  • Pangea

  • Volcanism (Siberian traps)

  • methane hydrate destabilization

  • impact

  • glaciation and climate changes

What went extinct completely at the end of Permian?

• Fusilina Foraminifera

  • index fossil for Carboniferous-Early Permian

  • already 90% extinct by P-T boundary, but last 10% was finished off by extinction event

• Tabulate Corals

  • radially symmetrical coral

  • consisting of two layers of cells united by a cellular layer of jelly

  • became fully extinct at Permian-Triassic boundary

• Rugose Corals

  • many different species present throughout the Permian

  • all became extinct during Permian-Triassic extinction event

• Trilobites

  • only two genera still existed near the end of the Permian

  • The order became fully extinct at the Permian-Triassic boundary

  • no survivors to the Triassic mixed faunas

What groups were severely reduced in diversity with some surviving species at the end of Permian?

• brachiopods

• crinoids

• bryozoa

• ammonoids

• coal swamp genera

• reptile families

• mammal-like reptiles

Why would Pangea have caused the Permian extinction?

• large mass of land, severe weather forced animals to change habitats

• global cooling, glaciation, and dry climate

  • large land area separated from ocean

  • lack of ocean-regulated weather

• These processes are slow processes, which may have caused the reduced # of genera or speciation, not abrupt extinction

Why would volcanism have caused mass extinction at the end of Permian?

• massive basalt eruption in a huge area

• eruption was fast < 1 mi. yrs.

• emission of gases cause global warming and ocean stagnation

• ocean anoxia caused marine mass extinction

• toxic gases causing extinction of land animals and plants

Climate Modeling

• end of Permian extinction 50k-80k years

• wiped out 95% of marine, 75% of land species

• human beings happened during P/T boundary

• sixth mass extinction?

Why could methane hydrate destabilization cause mass extinction at end of Permian?

• abrupt decline in carbon excursion, needs addition of isotopically-depleted carbon

• sulfur isotoeps recorded methane oxidation in ocean

• Problem: multiple carbon excursions have been found across P/T boundary; no direct methane-release features observed

Why could a meteorite impact have caused the mass extinction at end of Permian?

• Ir anomaly at P/T boundary

• finding of impact crater in western Australia

• impact debris (shocked quartz) near P/T boundary

• Problems: single or multiple meteorites; Ir anomaly is not as large as K/T boundary; how does it cause isotopic anomaly

Why could have ocean stratification and glaciation caused the mass extinction at the end of Permian?

• ocean was stratified due to formation of supercontinent and glaciation

• upwelling of 13C depleted, toxic water into shallow seas during deglaciation

What is crucial for doing a good science?

• hypothesis

• evidence

• scientific problem