Earth Sciences 240A - Lecture 27 - Mass Extinction Correlations

Periodicity: Extinctions

“Periodic Extinction of Families and Genera”: Raup & Sepkoski 1986

Statistically: 26 my (last 250 my period)

Causes

Nemesis

Planet X

Periodic galactic axis tilt

Other Suggestions

Nearby supernova

Galactic dust clouds

Changes in global climate

Endemic diseases

End Permian

Global, all environments, sudden

Common view: “A period when almost everything went wrong”

Impact?

Best: 2001 find: ‘Buckeyballs’: filled with gases;

Hungary,China, Japan

Discovered craters appear too small: off Australia ~OK; Subducted evidence?

Insignificant Ir

Maybe a comet? Low-metal asteroid?

Periodicity: Extinctions, Flood Basalts, Impacts, Magnetic Reversals:

Stothers & Rampino (1984 +)

Periodicity: 33 ± 3 my

Impact age clusters/flood basalt age clusters

Scenario:

Plumes/hot spots: 25-75% top asthenosphere

Impact = sudden decompression = flood basalts

Study 1: Pal & Creer 1986

“Turbulence in core from surface impact = magnetic field reversal”

Transmitted/consumed seismic energy from impact

Loper & McCartney (1991)

“No physical/mathematical reality to make use of seismic energy in core”

No correlation possible

Study 2: Muller & Morris 1986

Impact

Altered climate

Induced icehouse climate

Altered moment of inertia/rotation of Earth

Induced magnetic field reversal

Loper & McCartney 1991

No icehouse correlation with magnetic field reversal

Scrap it!

Study 3: Burek & Wanke 1988

Energy source: transformations to high pressure phases in lower mantle

Volume deficit would cause upward surge from core-mantle boundary = plume = magnetic field reversal

Loper & McCarney 1991

All computer models show energy surge would be downward, not upward

Model can’t possibly work

Conclusion

These studies can’t possibly support the Stothers and Rampino suggestion of periodicity for

Impacts

Plumes (flood basalts)

Magnetic field reversals

Mass extinctions

Ir anomaly/Impact/Flood Basalt

Earth’s crust: 0.02 ppb; Chondrite: 500 ppb; Deep-sea clays: 0.3 ppb;

Coal: as high as 3.0 ppb; KT: 5-7 ppb; Deccan Traps: 0.006 – 0.026 ppb

Hawaiian magma: 0.28-0.40 ppb (Partition 0.3% to atmosphere)

Mass Extinction Horizon Ir Anomalies Ref. Orth et al (1990)

End Ordovician: 0.058 (0.005 bgd)

Late Devonian: 0.160 (0.027 bgd)

Probably extraterrestrial

End Permian: 0.002; 0.025 (~ bgd)

End Triassic: 2x bgd

KT: same as everyone else

Only this one is unarguably extraterrestrial

Flood Basalts/Mass Extinctions/Mid-Cretaceous Superplume 120-125 myg

Superplume doubled formation of ocean floor; Warmest period ever

No correlation with mass extinction (actually the opposite!); Enormous oil, coal deposits

No ice; Deep ocean water 15-20o warmer

Global T as much as 14oC warmer

Arrangement of continental blocks: 1/3 of warming

Lack of ice/snow: 1/3 of warming

Superplume: 1/3 of warming

Correlation Conclusions

10 extinction events correlate with flood basalt eruptions

Of the 12 flood basalt eruptions reported since 250 mya, 9 correlate with extinctions

Eruptions on land versus under water

Second-Final Thought

If flood basalt gases are SO2 rich:

seas would be VERY acidic

some limestone would be dissolved

Added CO2 to atmosphere: VERY hot greenhouse

NO SUPPORT FROM O-ISOTOPES

Some geophysical evidence says Chicxulub is actually 300 km diameter (biggest ever??)

Final Thought

No field evidence supports correlation of impacts and flood basalts

 

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