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;
Discovered craters appear too small:
off
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
Next: Mass Movements