Clark R. Chapman

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Were Permian-Triassic Extinctions Sudden and
Caused by Impact?

• Clark R. Chapman
• Southwest Research Inst.
• Boulder, Colorado, USA

Meteoritical Society 2005 Gatlinburg, Tennessee,
USA 13 September 2005
2
A Big Interdisciplinary Issue

• From the perspective of planetary science, it is
  obvious that a comet or asteroid caused the K-T
  mass extinction
• As I will argue, the logic is overwhelming that
  impacts caused most mass extinctions
• Yet paleontologists, even those who support the
  K-T impact scenario, still argue that terrestrial
  causes for mass extinctions are at least as
  plausible as impact causation

They are wrong, in two ways Widely
reported specific evidence is not true The
philosophical stance is wrong
3
News Media Cry Permian-Triassic Boundary was
Gradual

• Science featured this article
• So it was in Science Express before publication
• It was on National Public Radio, MSNBC, etc.
• Major 4-pg. article published 4 Feb. 2005
• Rebuttal not published in hard-copy but in
  on-line edition, 3 June 2005

Abrupt and Gradual Extinction Among Late Permian
Land Vertebrates in the Karoo Basin, South
Africa Peter D. Ward, Jennifer Botha, Roger
Buick,Michiel O. De Kock, Douglas H. Erwin,
Geoffrey H. Garrison, Joseph L. Kirschvink, Roger
Smith
MSNBC, Jan. 20, 2005
Feb. 4, 2005
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Ward et al.s Data and Argument

• Total data set 126 skulls in 21 taxa over 240
  meters
• Evidence for abrupt extinction near horizon A
• Alleged gradual component based on 3 or 4
  left-most taxa
• Charles Marshall disputes methodology

June 3, 2005, Science on-line
Comment on Abrupt and Gradual Extinction Among
Late Permian Vertebrates in the Karoo Basin,
South Africa TECHNICAL COMMENT
Charles Marshall Museum of Comparative
Zoology Harvard University 26 Oxford
Street Cambridge, MA 02138, USA
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My Alternative Interpretation

• Taxa 4-6 Ward agrees to extinction at or near
  level A
• Taxa 7, 8, 10 abrupt extinction
• Taxa 9, 11, 12, 13 passed thru but went extinct
  later
• Taxa 14-21 orginated after abrupt extinction
• The whole issue rests with taxa 1, 2, and 3,
  represented by just 9 skulls altogether.
  Lets look at these 3 taxa more closely

A
(By the way, LOOK at those apparent error bars!
The fine-print calls them 20 confidence
intervals.)
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21
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How do Heights of 9 Skulls in Taxa 1-3 Compare
with Random Chance?
The 9 skulls

• Method distribute 9 items randomly between 0 and
  -60
• Ten trials are shown (actual skulls in column
  zero)
• Trials 1, 3, and 8 avoid the extinction level
  even more than do the skulls
• Plainly, there is no robust case for a gradual
  extinction!

7
Bold Claims Should be Based on Robust Statistics
3s

• In many sciences, 3-sigma confidences are the
  standard for proof
• Here, Ward et al. use 20
  confidence intervals
• Their table shows only 1 taxon avoiding the
  zero-level with much better than 50 confidence
  and it is based on just 2 skulls at exactly the
  same height!
• This is bad science, bad science-reporting, and
  Science magazine should be ashamed for burying
  the rebuttal in the on-line edition after
  trumpeting the original article

What are they?
Confidence (C) (extinction be- fore deposition of
Unit II) 0.875 0.5 0.52 0.31 0.2 0.17 0.13 0 .05 0
0 0
X
8
An Impact is Properly the Null Hypothesis for a
Mass Extinction

• The Earth has been struck by roughly half-a-dozen
  K-T-scale and larger impacts since the
  pre-Cambrian
• In terms of destructive energy per unit time
  delivered to the ecosphere, NO terrestrial
  process comes close
• Total liberated energy gt100 million megatons TNT
• Within 2 hours, entire globe is broiling oven
• Almost no refugia no time to move to a refuge
• Terrestrial causes operate over centuries to
  millions of years few are global in effect
• Time for flora and fauna to migrate and/or evolve
• Any hypothesized instantaneous terrestrial event
  (e.g. catastrophic sea-level rise) will not be
  global in its effects
• Catastrophic change requires suddenness

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Concluding Thoughts

• Widely touted evidence for a gradual component to
  the greatest mass extinction is based on faulty
  statistics
• The P-T mass extinctions, and the other big ones,
  must be assumed to be caused by the inevitable,
  catastrophic impacts Earth has sufferedunless
  contrary evidence is found.

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• The End