The Permo-Triassic Extinction: A Question of Timing

The Permian–Triassic extinction event (the Gre...

The P-Tr spike is at the middle - Image via Wikipedia

Guest post by Mark Hladik

Introduction

In a 31 August 2011 article A blast from the gas in the past, Anthony Watts and company at Watts Up With That discussed a new paper by Montenegro et al titled, “Climate Simulations of the Permian-Triassic Boundary:  Ocean Acidification and the Extinction Event”.  This paper places the blame for the extinction event on the ‘demon’ gas carbon dioxide which supposedly made the oceanic environment too ‘acid’ for marine critters to make their calcite/aragonite shells.

Standard boilerplate ‘carbon dioxide is dangerous’.  Nothing new here.  Many valid rebuttal points were made by the participants in the ensuing WUWT discussion thread.

In the course of researching this missive, the author found a very similar paper:  Saunders, A.; Reichow, M.; 2009; The Siberian Traps and the End-Permian mass extinction:  A Critical Review; Chinese Science Bulletin v. 54  # 1  pp 20 – 37, (hereafter SR2009).   This paper also points to significant environmental change from the out-gassing during the emplacement of the mafic rocks and their associated by-products, near the Permo-Triassic boundary.

There is no doubt that volcanism on the scale of the Siberian Traps would have a measurable impact on the environment.  The big question is one of timing.  Did the traps form in a time frame which would allow their impact to be a major cause of the extinction event?  Is there another possibility which needs to be explored further, and actually accounts for the likely sequence of events at the extinction?

We do not have perfect knowledge but we can look at data and information which cast doubt on repeated assertions made by those who are convinced that carbon dioxide represents a global danger.

Timing

Geologists have divided the history of the Earth into several time intervals.  For example, most everyone is familiar with the Jurassic Period, thanks to the popularity of the movies bearing the same name.  This is just one of thirteen such Periods, the Permian and the Triassic being the two under consideration here.  A fast and easy download comes from the Geological Society of America (www.geosociety.org/science/timescale) which at this writing has the 2009 Geologic Time Scale, with all of the subdivisions created by the geological community.  This time table is a summary of the monumental work by Gradstein, Ogg, and Smith, called “A Geological Time Scale 2004”, or GTS 2004, which would primarily be of interest to those working in the profession.  Many libraries have copies, and this author will be referring to some of the geochemical charts contained in GTS 2004.

Readers are cautioned that GSA 2009 and GTS 2004 are now somewhat out of date, and this author has recommended revisions to GSA.  While the changes are minor, they have a significant bearing on this article.

At this point, the reader may be asking, ‘why do the dates of geological subdivisions keep changing?’  This is a good question, and requires that the reader understand the origin of the concept of geological time.

Originally, geologic time was subdivided on the basis of the fossils found within the rocks themselves, with older, and often, more primitive life forms, being assigned to older strata.  These “older” strata tended to be deeper in the Earth, so there was little question of the relative ages of the rock layers.

With the advent of radiometric dating, it became possible to assign a time, as measured from the ‘present day’, to a specific rock layer.  Most people are familiar with carbon-14, and how it is often used to determine the approximate age of a sample of organic material, since 14C is present in all living things and the decay rate is well-established.  At the present time, 14C is useable for material less than 100,000 years old.

There are presently several dozen radiometric dating schemes in use, and often multiple methods are employed on a single sample as a cross-check.  As the geological sciences advance in methodology, and more samples are located and accurately dated, the time scale undergoes refinements, but the overall picture remains about the same.

For example, as an undergraduate in the 1970’s, the author memorized certain dates as the beginning times of the various Periods.  At that time, the base of the Cambrian Period was thought to be about 570 million years before present (abbreviated, ‘ma’, which stands for ‘million annua’).  That time was later revised to 540 ma, and in GTS 2004 and the GSA 2009 chart, the date has been further refined to 542 ma, plus or minus 1.0 ma
[i. e., 542.0 ± 1.0 ma].

What comes into play here, however, is the time for the beginning of the Triassic, or the definition of the Permian-Triassic boundary.  In the 1970’s, this time was thought to be about 225 ma, but it has since been refined to about 251.6 , plus or minus 0.4 ma, which is a phenomenal error constraint, considering the difficulties in getting an accurate date.

In the course of researching for this article, however, this author discovered that there has been an even further refinement to the dating of the Permo-Triassic boundary, and a reduction in the uncertainty associated with this important transition.

If the reader has downloaded the free time scale from the GSA, please make the following changes:

base of the Ediacaran:   now thought to be 635 ± 3.7 ma;   (formerly 630 ma)
base of the Triassic:      now thought to be 252.3  ± 0.3 ma;   (formerly 251.6 ma)
base of the Jurassic:      now thought to be 201.5  ± 0.6 ma    (formerly 201.6 ma).

It is likely that there will be further changes, but the trend for the ‘end-of-the-Permian/beginning-of-the-Triassic’ has been a consistent move towards an older time (viz., 225 ma, to 245 ma, and now 252.3 ma).  We are likely to see these revisions continue, especially as the geological community continues to explore this important boundary.

The question under consideration here is, ‘what caused the Permian extinction?’  As noted, numerous authors have pointed to environmental change(s) related to the Siberian Traps.  The most likely scenario put forth (and strongly advocated by SR2009) is that the Siberian Traps outgassed a great deal of carbon dioxide, causing rampant global warming (since, in their view, more carbon dioxide causes global temperatures to rise significantly), and the existing life forms could not adapt.  Montenegro et al carry this idea even further, citing the solution of increased carbon dioxide from the atmosphere into the oceans, changing the oceanic pH closer to a level of ‘acid’, which then inhibited the formation of hard shells of any number of marine invertebrates, causing them to die from predation, lack of food, etc, as well as from increased oceanic temperatures.

While an interesting hypothesis, this may not be the full story.  This author accepts that the Siberian Traps played some role in changing the global environment at the time the eruptions were taking place, but the big questions are, ‘when were those eruptions, and did they play a major role in the Permo-Triassic extinction event?’

Extinction Timing

This author will make reference to Dr. P. R. Janke of PanTerra (Box 556, Hill City, South Dakota 57745), who produces “A Correlated History of the Earth”, and who offers some insights into other possible causes of the Permian extinction event.  While certainly tentative, his hypotheses seem to be gaining ground, especially in light of the recent move of the end of the Permian from 251.6 ma to 252.3 ma.  Dr. Janke finds evidence that ‘global environmental change’ and the Siberian Traps, likely had very little to do with the Permian extinction event(s).

Anthony Watts has also posted an interesting chart on WUWT

which shows that prior to the terminal P/Tr event itself, a significant extinction was already underway.  In the 10 ma leading up to the P/Tr event, the rate of extinction was already greater than the K/T event (largely associated with Chicxulub).  The beginning of the extinction pre-dates the earliest Trap emplacement(s) by millions of years.

We must also ask, how long was the final P/Tr extinction process?  This remains an open question, but the best scientific minds on the planet are in general agreement that the final act was (geologically) rapid, occurring within a time span of 100,000 years, and possibly less (see http://www.le.ac.uk.gl/ads/SiberianTraps/).

This is a significant problem for the suggestion that the Siberian Traps had an effect on the Permian extinction.

The eruption of the traps themselves spanned an estimated 2 ma.  As is the case with many geological phenomena, the event had some beginning (likely at a low level of activity), built up to a crescendo, and then abated.  Even if it did start at a high level of activity, the first 100,000 years of eruptions did not produce 100% of the “extra” carbon dioxide.  If it is found that the terminal extinction occurred even faster than what is currently thought, say, e. g., covering some 50,000 to 75,000 years, then we are forced to question how the (slow-acting) geochemical mechanisms managed to dissolve the initial amounts of “extra” carbon dioxide into the existing oceans, given that the world was in the process of “warming” at the same time, and ‘warmer’ oceans outgas carbon dioxide, instead of taking it into solution.

A warmer world and ocean acidification (all the rage in the CAGW community today) might account for some of the extinction in the marine world, but how do ‘acidic’ oceans cause terrestrial plants and animals to go extinct at the same time?

Two lines of evidence suggest that the “extra” carbon dioxide from Siberia did little to affect the paleoclimate.  Firstly, GTS 2004 has geochemical plots, and the δ18O charts (a widely-used paleotemperature proxy) show little, if any, change across the time boundary.  Secondly, we would expect little change in temperature, even if the amount of carbon dioxide in the atmosphere increased, since carbon dioxide’s ability to cause warming is asymptotic, beyond a concentration of about 300 ppm.  The most widely accepted model of carbon dioxide concentration (Berner et al, GEOCARB III) indicates that the concentration likely changed from ≈3000 ppm to ≈4000 ppm, during the latest Permian and earliest Triassic. It’s a large increase to be sure (approximately 33%), but it should have very close to zero temperature effect, and GTS 2004 bears this out.

The biggest problem with the Siberian Traps hypothesis, however, comes from the dating of the traps themselves.  Recall that the generally accepted time for the end of the Permian (and beginning of the Triassic) has recently been placed at 252.3 ma with a ± 0.3 ma error estimate.  Again referring to the University of Leicester (referenced above), they show a central tendency date for the Siberian Traps as around 250 ma; the earliest radiometric date comes in as just older than 252 ma.  In either case, if these dates are valid, then the majority of the Siberian Traps would seem to POST-date the Permo-Triassic extinction by about a million years, and possibly more!

So how do we explain such a phenomenon, given the magnitude of the event and the questionable evidence for a climate catastrophe?

“A Correlated History of the Earth”

The seventh edition of Dr. Janke’s monumental work is copyrighted 2010; this author is in communication with Dr. Janke regarding some minor revisions to his time chart, especially with the newest base times put into place the previous calendar year.

Dr. Janke shows, among other things, a listing of significant events such as the Siberian Traps, and paleogeographic reconstructions, based on those of Dr. Christopher Scotese (www.scotese.com), which are widely considered to be among the best ever.  He also has a summary of the fluctuations in CO2 concentrations.  If one has not seen this, be prepared for a shock; the amount of information contained within this single chart is exceptional!

A Correlated History of the Earth also contains a column listing extra-terrestrial impact events.  The Chicxulub impact at the Cretaceous/Tertiary boundary (the “K/T Event”) is shown right at 65.5 ma, the now-accepted time for the extinction of the Dinosauria.

The most compelling item about this column on Dr. Janke’s chart is the listing of impacts (yes, plural!) at the end of the Permian.  Within the error limitations of impact event timings (especially older impacts), there are five probable impacts at the Permian/Triassic boundary:

Falkland Islands (part of South America at the time);
Wilkesland (Antarctica)
Gnargoo (Western Australia)
Bedout (offshore Western Australia)
Arganaty (central Kazakhstan)

As remarkable as this possibility is, it gets even better:  the first four events, allowing for the reconstruction of the paleogeography at the time (see Scotese), come suspiciously close to a straight line, not unlike a multiple-impact from a broken-apart celestial body, similar to Comet Shoemaker-Levy 9’s impact on Jupiter in 1994.

The Wilkesland impact structure has an estimated radius of 120 km; for comparison, Chicxulub is about 80 km.  It would seem that the Wilkesland structure, if verified, was potentially sufficient to cause the entire extinction event.  The possibility that there were some “insurance” impacts at the same time suggests that the Siberian Traps were a minor influence, and not necessarily the proximate cause of the extinction.  We have also previously established that the Traps likely post-dated the extinction itself.

In the same vein, we cannot completely rule out antipodal genesis for the Siberian Traps; the four ‘straight-line’ end-Permian impacts could have been an instigator of the Siberian volcanism, if the antipode hypothesis is valid.  Given the proximity, it would seem more likely that the Arganaty impact helped to initiate the Siberian Traps, the event being near the southwest fringe of the Asian LIP (large igneous province).  Perhaps this will become an avenue of further research, free of CAGW dogma.

Obviously, the biggest problem with this suggestion is the lack of an iridium-rich layer, as is associated with the Chicxulub event.  We do know that preservation in the geological record tends to be hit-and-miss, and the older an event is, the less likely that it has been preserved.  The author previously stipulated that there was probably some environmental influence(s) from the Siberian Traps.  If carbon dioxide was outgassed in significant quantities, then it is likely that sulfur and sulfurous compounds were also injected into the atmosphere.  It would take little imagination to see some type of global ‘acid rain’ removing a large part of the fresh iridium-rich layer of impact debris, if the hypothesized impact(s) at the Permo-Triassic boundary occurred.   We know that many land plants were exterminated at this time, so logically, the rate of erosion could have increased substantially, until land plants re-established themselves (in the Triassic), and stabilized soil formation.

(For those who might not otherwise know, groundcovers such as grasses had not evolved yet, so any soil stabilizers would have been restricted to large vascular plants.)

Conclusion

CAGW alarmists seem to be singularly obsessed with carbon dioxide, and its supposed effects on the global environment.  The lengths to which these individuals and groups will go to tie carbon dioxide to absolutely everything, even in the face of contradictory evidence, is something few of us will ever understand.  Even a political agenda as a prime motive does not do justice to the fanaticism on display.

Consider that there is reason to suspect the idea of the Siberian Traps as a prime cause of the Permian extinction, the most extensive, documented extinction on the planet.

Consider that the skeptical side of the argument accepts and knows without doubt that global climate has always changed, that the current change is not unusual (we can  discuss EPICA and Vostok at a later date), and that carbon dioxide emissions have little to do with global climate change.

We can understand that individuals in the Meteorology community might not be aware of the type of data available on the Internet.  Once they are made aware of such data, we could reasonably expect that these individuals might re-examine their positions, and understand the lack of correlation between global temperatures and atmospheric carbon dioxide concentrations.

Members of the geoscience community do not have such an excuse; these individuals are the curators of the knowledge of what has happened in the past, and should know better.  SR2009 makes the blanket assumption that any change in carbon dioxide automatically means a corresponding change in global environment/temperatures, almost in linear lockstep, when we can demonstrate that the levels of CO2 in the Permian atmosphere were such that any change would have had a trivial effect on temperatures.

Montenegro et al fail to recognize that hard-shell organisms evolved at a time when carbon dioxide concentrations were on the order of 6,000 to 7,000 ppm, so that any alleged “ocean acidification” because of the Siberian Traps outgassing would have had a negligible effect on their descendants.  During the preparation and editing of this article, a new post occurred at JoNova’s website, called The Chemistry of Ocean pH and “Acidification”.  [www.joannenova.com.au/2011/11/the-chemistry-of-ocean-ph-and-acidification/#more-18584]   This article summarizes the current information on the effects of increased carbon dioxide on ocean pH, in light of the burning of fossil fuels, and the change in atmospheric chemistry.  It is a worthwhile read.

For much of geologic history, the Earth has been warmer than it is now, with no demonstrable harm to the organisms in existence at the time.  In-so-far as we can tell, life flourished in almost every part of the existing land, and has thrived/survived substantial and innumerable “climate changes”, not to mention impact events.

The reader is free to doubt what you read here, but the geochemical charts contained in Geologic Time Scale 2004 represent the current state of the art.  Even a cursory examination of the δ18O paleotemperature proxy should give pause to even the most die-hard CAGW advocate.  As we know, ‘there are none so blind as those who will not see.’

Appendix

The definitive paper on the radiometric dates for the Siberian Traps is also authored by Reichow and others.  While the University of Leicester summary (above) has an excellent reference to the accepted radiometric dates, this paper

http://le.ac.uk/gl/ads/SiberianTraps/PDF%20Files/Reichow%20et%20al.%202009.pdf

gives the most comprehensive overview of the current research on the dating of the Traps.    With the exception of three dates which come before the newly-accepted boundary between the Permian and Triassic, and three dates which are significant outliers (almost ten million years after the transition), the central tendency of the eruptions of the Traps is about 250.1 ma, well after the terminal Permian extinction was complete.

The specific dates are as follows:

248.1 ma
248.4
248.6
248.7
248.8
248.9
248.9
249.0
249.1
249.2
249.4
249.5
249.6
249.7
249.7
249.8
249.9          [median]
250.1
250.1          [mean and mode]
250.1
250.2
250.2
250.4
250.5
250.5
250.6
250.8
250.8
251.7
251.8
———-   Permo-Triassic boundary at 252.3 ma  (± 0.3)
252.6 ma
253.3
253.4

About these ads

67 thoughts on “The Permo-Triassic Extinction: A Question of Timing

  1. God bless Kate Humble. Goodness knows how she got her latest program past Richard Black the CAGW gatekeeper at the BBC.

    I realise that this is a trilogy but in the first episode she explained the Earth’s climate without once mentioning CO2.

    It is called EARTH’S AMAZING JOURNEY. I do hope you peeps outside of Britain can access it.

  2. It is absolutely wonderful what you will find at this site. I’d never heard of the Antipodien comet/meteorite strikes before and was only vaguely aware of the Siberian Traps! Now I need to do some further research on these subjects.

  3. I’ve seen no discussion on the weather caused by a basalt flood event.
    We know relatively small extra heat can wind up a serious hurricane. Surely then 1000s of sq. miles of ground temps well above normal due to 24/7 geologic heat will cause a hyper-hurricane.
    The thing would have been like Jupiter’s Red Spot dominating global weather and spawning F5 hurricanes for breakfast.
    Could such world-wide weather mayhem have caused a mass extinction?

  4. Yet another discussion of the PT extinction that doesn’t even note that it coincides with a major galactic cosmic ray flux minimum, when our solar system was between two spiral arms of the galaxy and as a result had relatively few cloud condensation nuclei created by the GCR mechanisms that are now well on their way to being understood thanks to CLOUD, SKY and other experiments.

    It was the stylized representation of Shaviv & Veizer’s “Celestial driver of phanerozoic climate?” (2003) in Svensmark’s Cosmoclimatology survey paper (A&G 2/2007), see Figure 8 that set me on my 5 year mission to take brickbats and abuse from anonymous blog sockpuppets happy to torment anyone wishing to take on the AGW “mainstream” science.

    At an AGU talk two years ago Dick Alley got away with claiming CO2 had to be the cause of the PT because ‘there just wasn’t anything else’. There is. The hottest periods were during GCR minima, the coldest were during GCR maxima. And the PT was the maximum over the last 500+ million years.

    How about it? Think there *might* now be enough supporting science for us to suggest a major cause of the Great Dying was due to the fact that, no matter what the sun might have been doing at the time, there just were not many GCR and the planet would have have fewer clouds to reflect sunlight as a result?

  5. That’s what happens when you stay in your “comfort zone” and try to explain EVERYTHING from your own paper thin area of expertise. Einstein tried to explain the universe through Mathematics, Freud the primitave brain, Darwin mutation, etc…

    The big picture is bigger than anyone’s head. You get to work on your tiny pixle but you don’t get to see more than a fingernail scratch your whole lifetime. Most things are unknowable in whole. When our brains are big enough to stop us from whacking the big black rectangle from the sky with femur bones, we’ll be able to look back at how foolish we were to think CO2 was bad.

    We still won’t know much, We’ll know a thousand times more than we do today, but still not much.

    Laugh at me, you’ll know how right I am in about 50,000 years!

  6. The strongest contender for the PT extinctions is sea-bottom eruptions of H2S, truly a demon gas. Heavy clouds of H2S would wander the world on an extinction spree.

    Just to add to the fun, O2 dropped to 10%.

    Whatever CO2 was doing then, it didn’t kill a single PT victim.

  7. As the original proposer of the ‘possible’ impact origin of the Bedout Structure (in a non-peer reviewed publication), I have been reasonably assured by many other geological coleagues that it is non-impact in origin. I suggest that you look up some of the relevant literature on the internet before including it in your otherwise excellent article.

    By the way, the absence of an iridium layer does not precuse an impact origin, it depends on the geochemistry of the impactor, and there are iridium-rich layers in the Devonian of the Canning Basin in Western Australia where the element is apparently concentrated by biological processes seemingly un-related to impact.

    Ciao

    John Gorter

  8. Even a political agenda as a prime motive does not do justice to the fanaticism on display.

    But religious fanaticism explains it for this subgroup of CAGW believers.

  9. “…CAGW alarmists seem to be singularly obsessed with carbon dioxide, and its supposed effects on the global environment. The lengths to which these individuals and groups will go to tie carbon dioxide to absolutely everything, even in the face of contradictory evidence, is something few of us will ever understand. Even a political agenda as a prime motive does not do justice to the fanaticism on display….”

    Does an estimated £100bn Carbon Trading market possibly begin to explain it? And that would only be the start…

  10. Rhoda Ramirez [March 6, 2012 at 3:56 pm]

    “… I’d never heard of the Antipodien comet/meteorite strikes before and was only vaguely aware of the Siberian Traps!… ”

    Then you may like:

    “Antipodal hotspots and bipolar catastrophes: Were oceanic large-body impacts the cause?” by Jonathan T. Hagstrum

    http://www.mantleplumes.org/WebDocuments/Antip_hot.pdf

  11. There is a major problem with almost all papers related to the Permian – Triassic extinction event, and that is perception. The end of the Permian was ridiculously species rich, with an amazing level of hyper-specialization. A little change in the environment is all it takes to bring the whole thing down. And just because the number of species diminished radical does not mean that life was wiped out.What happened was that the generalist species populations increased to fill the areas vacated by the now, unequipped specialists.

  12. The δ18O isotopes show a major excursion at 251.4 Mya indicating a very significant cooling event at this time versus the typical δ18O isotopes around the period which indicate it was very warm. The excursion starts to become apparent at about 253.7 Mya so this might have been date of the first eruptive events.

    This paper has the dating of the first event at 252.7 Mya so my money is still on the Siberian Traps being responsible.

    http://www.igm.nsc.ru/labs/lab212/~safonova/pdf/epsl-reichow2009.pdf

  13. “the first four events, allowing for the reconstruction of the paleogeography at the time (see Scotese), come suspiciously close to a straight line,”
    I looked but couldn’t find said view.
    ground-breaking research ! (pun intended)

  14. Sandy says:
    March 6, 2012 at 4:04 pm
    I’ve seen no discussion on the weather caused by a basalt flood event.
    We know relatively small extra heat can wind up a serious hurricane. Surely then 1000s of sq. miles of ground temps well above normal due to 24/7 geologic heat will cause a hyper-hurricane.
    The thing would have been like Jupiter’s Red Spot dominating global weather and spawning F5 hurricanes for breakfast.
    Could such world-wide weather mayhem have caused a mass extinction?

    Hurricanes depend on latent heat of water and the ‘wet adiabatic lapse rate’ differences to the ‘dry adiabatic lapse rate’. This is why hurricanes develop over water and fade out over land; indeed dry air being sucked into a hurricane will kill it. However hot they were, the Siberian eruptions would not have provided the impetus for hurricanes as they would be very dry events.

  15. An insightful article that sheds some light on this mass extinction. There is a new theory that is able to explain this extinction and most other mass extinctions…..no asteroid impact required.
    Visit http://www.dinoextinct.com and click on ‘The Gravity Theory of Mass Extinction’.

  16. I favour as the cause, very large scale peat fires due to falling sea levels or the enclosing of the Tethys Sea drying out peat bogs, and the smoke blocking sunlight for many years

    As we know from the present, drain and dry out a peat bog and sooner or later lightning will start a fire that will burn for many years.

    Quantitative analyses of combustion-derived PAHs and BC demonstrate anomalously high concentrations in the boundary event beds that coincide with the mass extinction horizon. The prevalence of parent polynuclear aromatics (e.g., phenanthrene) in PAHs, together with non-metric multidimensional scaling analysis, confirms that the PAHs are mainly derived from vegetation burning instead of having a coal and/or oil origin.

    http://www.sciencedirect.com/science/article/pii/S0016703711000445

    The smoke would have been particularly thick and continuous over the peat beds, which perhaps explains the Coal Gap – peat forming plants disapeared for millions of years after the P-T boundary .

  17. Not only do volcanoes spew out huge amounts of sulphourus gasses, they also spew out selenium. The Se/S ratio of volcanic sources is 10 to 100 times the normal background. As both Se and S mineralize very quickly in hypoxic oceans, the Se/S ratio should tell you if you have a major volcanic extinction.

  18. Reblogged this on gottadobetterthanthis and commented:
    Amazing! The information presented and the references given could take years to appreciate. I re-emphasize the reference to Dr. Christopher Scotese ( http://www.scotese.com ). Awesome web site. “During the last 2 billion years the Earth’s climate has alternated between a frigid “Ice House”, like today’s world, and a steaming “Hot House”, like the world of the dinosaurs.” Dr. Scotese. Most of earth’s history has been significantly warmer than today, but it is also worth noting that on an absolute scale, the earth’s temperature has changed very little for over two billion years!

  19. Thanks to all for the comments, both pro and con.

    Greg Goodnight: see Dr. Janke’s chart(s). He is in favor of a similar hypothesis, and discusses it better than I ever could. I think it is an interesting possibility, not a definitive answer.

    William Martin: ditto on Janke; he uses the Scotese reconstructions, and places the approximate locations of the impact event (hypothetical and confirmed) onto his charts. Scotese just does the paleogeographic reconstructions, replete with possible subduction zones, volcanic fields, hotspots, etc, but no impacts.

    Thanks again to all, I will check back as often as possible, and my best regards, and thanks to Anthony and moderators,

    Mark H.

  20. Gentlemen,

    Great site. My first post here.

    Along a similar line, Prescott et al have a new paper in PNAS attributing Quaternary megafauna extinctions to climate change. I haven’t read the paper, but I’m familiar with the general setting. Here’s the scoop:

    Over the last 2my, aka the Quaternary Period, the earth has experienced many cycles of glacial advance and retreat. The peak of the last glacial advance, or last glacial maximum (LGM), occurred about 20,000 years ago. Previous glacial maxima occurred at approximately 140ka (140,000 years ago), 250ka, and 340ka. Less pronounced glacial maxima occurred many times, extending back to the onset of the Quaternary geologic period, 2my ago. Throughout the many glacial advance and retreat cycles of the Quaternary, no major extinctions occurred anywhere in the world – until the last cycle.

    During the last glacial cycle, however, large animals, aka the “megafauna,” throughout the world disappeared. The cause of this extinction has long been a topic of intense discussion. Nonetheless, it’s well established that, on all continents except Europe and Africa, the extinction occurred shortly after the arrival of humans. Notably, human arrival takes place at different times in different places, starting as early as 40,000 years ago in Australia, and ending the Americas about 12,000 years ago. Many paleontologists, including the Australian writer Tim Flannery, have long concluded that these extinctions result from the invasion of a new species on each continent – humans. This hypothesis has been dubbed the “overkill” hypothesis.

    Now, however, striking new *quantitative* research by Prescott et al (PNAS) claims to show that the megafauna extinctions occurred because of humans *and* climate – even though more significant climate events in the past – sans humans – caused no extinctions.

    The climate bandwagon is hauling arse! Best get on while the getting’s good!

    http://www.pnas.org/content/early/2012/02/29/1113875109.abstract?sid=078b8a80-7f73-4c1f-9146-053bfa077fbd

  21. This is sort of related. It’s a mystery surrounding the extinction of the wooly mammoths, which apparently existed in large herds, until… what?

  22. In the earlier part of the Permian, prior to the extinction time frame, by some assessments, CO2 was quite low. A related question and a very grave one – does low CO2 predispose the ecosystems of Earth to be vulnerable to relatively sudden stress (for example, a bolide or asteroid strike, a solar flare, other extra terrestrial fluxes, higher than normal volcanism, etc)? If the answer to this is yes, we need to be worried. 400 PPM is low by the standards of overall Earth history.

  23. it’s fairly safe to say that global cooling is the new global warming mantra.
    as always, the public are subjected to a scare campaign.
    I’m academically interested in this post, but wonder if our time could be better spent. we seem to have enough information that extinction events occur via volcanism, meteoric impacts, and ice ages. granted we are forced to debunk the fraudulent global warming ethos.
    Jim (Harvey), Tim Flannery claimed that sea levels would rise by several metres, then bought a waterfront home. he claimed Australia could expect permanent drought, and 3 desalination plants were built on his recommendation. Australia is currently experiencing record floods, and the desal plants lie unused.
    I really don’t think a runaway heat event is going to happen – is there such an event in the record ? n.o.
    my time is required elsewhere.

  24. Dodgy Geezer says:
    March 6, 2012 at 5:14 pm
    “Does an estimated £100bn Carbon Trading market possibly begin to explain it?

    I don’t thinks so. Those of that type generally do not display much fanaticism. Those that show fanaticism likely cannot explain the mechanics of a market. If you want to see this in action, write a short letter to your local newspaper and express the view that carbon dioxide at levels now in the atmosphere and for the next 50 years is more likely good than dangerous. You should ask the editor to not use your real name on the letter, though.

  25. There are oceanic acidification maps on the ‘net. Chesapeake Bay and the west coast of South America have a pH of 7.9, the first to do with surface runoff impacts, the second, due to upwelling from oceanic deeps. Both are high bio-diversity and bio-mass areas, both with a lot of calcareous organisms. There is no observational evidence that naturally lower pH oceanic waters dissolve carbonate-secreting organisms.

    Aragonite, the isomoph of calcite, is what calaceous-shelled organisms lay down. It dissolves more readily than calcite, so the worry that a lower pH will effect them is, in theory, understandable. Has rainfall become more “acidic”? You would expect that to be the case. I’m not hearing it, only the claim that sea-water samples from the 1800s were 8.2, and now the seas are 8.1. That’s a lot of CO2 sequestered in the oceans that is not showing up in the rainfall, which you would expect to be the main way it gets into the water (the wave action/interface may be very significant, I grant you. I still expect to see a change in rainfall visible in ice samples).

  26. Thanks to Mark Hladik for this informative article, and to John D. Gorter for the relevant additional information. It’s commentaries like this that make WUWT the best science website on the internet.

  27. From the Book “Recovery and Refining of Precious Metals” by C.W.Ammen Iridium is insoluable in all acids including aqua regia. That would take acid rain out of the picture. It leads to the question if all later impacts had this Iridium tracer if not it was due the eather the composition of the metior or the area impacted. A Gkobal cooling event and erosion would also be reas0nabl.

  28. John

    I have been reasonably assured by many other geological coleagues that it is non-impact in origin

    Consensus does not confirm.

  29. LeoLurking: Thanks! I found some stuff on the Siberian Traps but was at a loss as to how to even begin looking for the Antipodes stuff.

  30. Excellent and informative article , many thanks.

    One logical error it seems:
    >>
    how the (slow-acting) geochemical mechanisms managed to dissolve the initial amounts of “extra” carbon dioxide into the existing oceans, given that the world was in the process of “warming” at the same time, and ‘warmer’ oceans outgas carbon dioxide, instead of taking it into solution.
    >>

    Water out-gasses as temperature rises *all other conditions being equal*. An increased concentration of atmospheric CO2 would cause more absorption *all other conditions being equal*.

    Both of these opposing effects would have to be quantified and it is certainly much more complicated anyway.

    >>
    In the 10 ma leading up to the P/Tr event, the rate of extinction was already greater than the K/T event (largely associated with Chicxulub).
    >>

    http://www.geocraft.com/WVFossils/Carboniferous_climate.html

  31. old44 says:
    March 6, 2012 at 5:56 pm

    One of fourteen such Periods, we are currently in the Age of Stupid.

    Keeper!

  32. Lonnie E. Schubert says:
    March 6, 2012 at 7:24 pm

    Blogvertise [ blog ver tize ]
    1. Transitive and intransitive verb – to exploit one blog to the advantage of another without appreciably altering the original content. To leech.

    2. Transitive and intransitive verb – to annoyingly announce a second source of a copy of the original with the intent of driving up the number of hits at the second site. To piggyback on a successful injection of interesting information while avoiding the initial effort. To leech.

    3. Transitive verb – to share information you didn’t think of but thought your blog reader should know about. To leech.

    From Peterson’s “Reduction and Analysis of Blog Predation: Adaptive response to competitive blog behavior”. The breakout work “I link therefore I rock” paper is targeted for 2012 release and is from the “Blogging as War – Alone at the Top” series.

  33. Fascinating again. Thanks Mark. Smokey your ref is to an event a lot later – but it is indeed a fascinating reference as well.

    I was put on to a book I now tend to regard as an important yardstick, by which to measure material, several years ago, by a commenter here! Magnetic Reversals and Evolutionary Leaps, by Robert Felix. Not necessarily infallible, but a very important gathering-together of observations that usually bypass orthodoxy.

  34. The Null Hypothesis just grew fangs and claws. That’s a whole lotta potent “natural variation” to understand and dismiss before CO2 gets a look-in.

  35. Smokey – that link should come with a warning! Do not click on it unless you’re prepared to spend the next couple of hours contemplating the mysterious demise of the mammoth.
    Two questions . . first, where is the text from? Second, they don’t seem to consider the ‘day after tomorrow scenario’. Is that because of the age of the text, or is the super cell scenario highly implausible.

  36. These researchers do not seem to be real geologists otherwise they would know that aragonite sea shells thrived in conditions of much higher atmospheric CO2 content than that at the P-Tr boundary. Corals too loved the extra CO2.

    Their chemistry is poor as well. Ocean pH varies over the surface between 7.4-8.3 and has done for at least 400Ma. This pH band is not acid.

  37. Thanks Mark. The one thing I had been willing to admit as a possible exception to the line that “there is no actual evidence for climate changes being driven by climate” were claims of CO2 driven extinction events, just because I didn’t know anything about the subject. Nice introduction!

  38. Yeah, that was supposed to say: “there is no actual evidence for climate changes being driven by CO2.”

  39. Stephen

    Thanks for you observation re consensus, at the risk of joining a consensus, I agree with you.

    However, there has been a lot of work done on basal cores from two petroleum wells (Bedout-1 and LaGrange-1) on the Bedout feature and a lot of seismic shot that seems (!) to indicate a non-impact origin. In addition, I have seen some deepwater offshore seismic profiles to the west of Bedout that look quite similar in seismic signature, and while the particular ones I refer to have not been drilled, I think it unlikely that we have a cluster of large scale impacts (i.e. greater than 50 km diameter), although they do exist (e.g. Tookoonooka and Talundilly, Eromanga Basin, SW Queensland).

    Ciao

    John

  40. Why would Iridium only come from météor impacts ? Traps come from the undifferenciated lower mantle; so why would its geochemistry be different from that of meteors?
    Sorry for my vocabular; I am French

  41. Mantle plumes which cause extinctions tend to start violently and then decline. This because as the massive plume rises and nears the surface it mushrooms, and therefore the initial event is often the most violent. For example, most hot spot volcano tracks have large and extensive volcanic provinces as evidence of their initial formation when they first breach the surface, they then peter away and decline over millions of years. So your suggestion that the event built over time to a late crescendo is actually the opposite of what happens with mantle plumes-they start violently and then decline.

    This initial ultra-violent event may be buried deep within the earliest layers and therefore not at surface and therefore not dated, supporting the earlier date of the extinction event.

  42. John Alldritt:

    As someone else said, the best part of this particular blog is the level of scientific expertise exposed. You are no exception!

    To clarify, the intent was to suggest that any layer of material (impact detritus, if there was any) would have had any rare-earth minerals contained within the layer. This layer of material could have been subjected to a higher level of erosion, due to the loss of plant life, and ultimately deposited elsewhere. The “elsewhere” part of this narrative is the problem. As we know, any sediments reaching the oceans have been subducted long ago, or if not subducted, then so highly altered by tectonic processes as to be nearly unrecognizable (e.g., Fransican Tectonic Melange, California).

    I do appreciate your information, and thank you for the chance to clarify my statements. Any further modifications I make to the text will likely incorporate a better explanation for the absence of an ejecta blanket.

    Regards to all, and thanks for the many comments,

    Mark H.

  43. Greg Goodknight says:
    March 6, 2012 at 4:12 pm

    The change GCR flux due to the solar system moving into the region between the galactic arms, would have taken millions of years. Both coming out and going back in. Plenty of time for life to adapt.

  44. Would it be possible for Mark Hladik to get some help to work this into a paper, possibly a comment/response to be published in AGU’s PALEOCEANOGRAPHY?

  45. CAGW alarmists seem to be singularly obsessed with carbon dioxide, and its supposed effects on the global environment. The lengths to which these individuals and groups will go to tie carbon dioxide to absolutely everything, even in the face of contradictory evidence, is something few of us will ever understand.

    I recently came across a book called Future Babble that seems to address this sort of thing, with regard to “experts” who forecast (politics, economics, or whatever), and who are so often wrong. The book categorizes people as “Hedgehogs” or “Foxes” – Hedgehogs (the “experts”) only know one thing, so interpret EVERYTHING in light of that one thing, which often makes them wrong. They are unable to account for anything other than the one thing they know.

    I think we see that happening in the climate field.

  46. There are two facts often lost to people using geologic timeframes in the context of climate change, one is the different concept of time and the other is preservation.
    Preservation comes into this particular argument when the idea of a bollide event is dismissed due to lack of evidence. Although the continents were organized considerably different at the end Permian oceans still made up the majority of the earth’s surface. As a consequence impacts would almost certainly have been more prevalent in the oceans and these could not possibly be preserved simply because the worlds ocean crust is continually regenerated such that the oldest crust is about 200 MY or so (too young for this event). Hence one would be missing any evidence of impact in the oceans during this timeframe.
    The concept of time is often hard for people to really comprehend. The arguments about climate science specifically centre around a timeframe of about 100 years and in reality deal mostly with the period from about 1950 onwards. To listen to the climate modelers one would expect almost immediate response from temperature to increased GHG content in the atmosphere. The narrowest estimate I have come across for the length of time during which the mass extinction event(s) at the end Paleozoic took place is about 80,000 years (based on some work Paul Wignell did in Greenland as I remember). Think how long 80,000 years is and also put it in the context of how many species have disappeared or appeared on the earth in the past 80,000 years and the fact that North America probably wasn’t even inhabited by man much more than 20,000 years ago. This is a long period of time and hardly instantaneous as climate models would require for GHG’s to have a role to play. He further suggested that the last phase of that extinction might have coincided with a massive methane outgassing which would have happened over a period of 5000 years. Again, hardly simultaneous. This would be a bit like blaming the activity of ancient Egyptians for our current climate.
    Now much of this has to do with the error bars you deal with in age dating but it still requires caution in context of climate change discussions.

  47. Could a perpendicular meteor strike create a shock wave that triggered the traps? Then you would have two consecutive events, explaining the double spike and extended period of extinction. I’ve suspected the Scotia Plate near the Falklands, since it was near the southern tips of South America and Africa, and the upwelling from a nearly perpendicular strike could explain the deposits of heavy metals in South Africa. Whether a meteor strike could trigger the traps halfway around the world at a later date, I’ll leave up to experts to debunk.

  48. P. Solar:

    Thank you for the very insightful comment. As you have pointed out, my language was (once again) imprecise and improper.

    I agree with your statements. Do recall that the individuals who believe that the Earth (and oceans) warmed up are the various authors (Saunders, Reichow, Montenegro, etc) who have the paradigm that more CO2 means increasing temperatures. My personal feelings are that the injection of aerosols and any smoke particles from ordinary combustion, resulted in global COOLING, if anything. Referring to Veizer and GTS2004, there is little evidence of any significant global temperature change at the boundary, but the Early Triassic does show a generalized decline in temperatures. This would have been well after the mafics were emplaced. Further, cooling oceans would have become more “acidic” as CO2 dissolved into them, regardless of the CO2 partial pressure.

    Thingadonta:

    I would tend to agree with you, but there is no *requirement* that the initial event be large, explosive, all-encompassing; note that the Traps took several million years to emplace, and some 80%+ of the dates post-date the terminal event itself (which was likely tens of thousands of years in the happening). As far as I know (and I would appreciate more information if anyone has it), the Columbia River basalts/Snake River Plain were a [relatively!] quiet event, and appear to have been created by the Yellowstone plume, which has episodic violent eruptions even today (not in recorded human history; we see the results from the ash layers downwind of the Yellowstone caldera). The better analogy might be Hawaii; virtually uninterrupted since the first Emperor Seamount was emplaced way-back-when … …

    Kip Hansen:

    Appreciate the compliment, but it is unlikely that this missive will be seen outside of WUWT. Even though I am a Fellow of GSA, I do not follow the *meme*, so my peer-reviewers would reject it on the title alone. Also, there would be copyright issues; since Anthony has chosen to publish this text here, he, in effect, now “owns” it, and would have to agree to release the thesis to another party. I would not hold it against him for refusing to do so; his blog, his right to operate it as he sees fit.

    Thanks again for all the comments, and my best to all WUWT participants,

    Mark H.

  49. The Wilkesland impact structure … the lack of an iridium-rich layer

    I’ve pondered whether the Siberian Traps may have been caused by a meteor that punched through the crust. The primary debris would be from Earth’s crust & some mantle with little iridium.

  50. “Montenegro et al fail to recognize that hard-shell organisms evolved at a time when carbon dioxide concentrations were on the order of 6,000 to 7,000 ppm, so that any alleged “ocean acidification” because of the Siberian Traps outgassing would have had a negligible effect on their descendants.”

    Perhaps by the time of their extinction they had evolved further to no longer be able to withstand relatively abrupt changes in such levels of CO2 and acidification? What were the CO2 levels at various times along the time line from first evolution to extinction?

  51. John F. Hultquist :March 6, 2012 at 8:58 pm

    quoted Dodgy Geezer :March 6, 2012 at 5:14 pm
    “Does an estimated £100bn Carbon Trading market possibly begin to explain it?”

    and replied:

    “…I don’t think so. Those of that type generally do not display much fanaticism. Those that show fanaticism likely cannot explain the mechanics of a market. …”

    John, I think it does. Those who would trade in that market, and harvest their commissions and fees, have had great interest in marketing this to the ‘gullible masses’ (excuse the phase)..
    and, until recently, they’ve done a pretty good job of that. Under older systems of communication and information sharing, with no Internet, they’d have probably succeeded.

    -The US government has provided over $79 billion since 1989 on policies related to climate change.
    - Carbon trading worldwide reached $126 billion in 2008
    -Experts predict the carbon market will reach $2 – $10 trillion making carbon the largest single commodity traded. Banks are calling for more carbon-trading.

    I’ve never really thought of the whole CAGW thing as a conspiracy – more of a loose alignment of the self interested:

    1.Governments of course love it and leap upon it immediately – something to tax, regulate, licence, charge fees and also a wonderful distraction (a very important component of governing).
    2.UN and IPCC love it – funding and growth.
    3.Financial institutions and banks love it (see financials below – enough said)
    4.The scientists of course go where the funding is; that is fair enough. I suspect some of the more prominent figures are motivated by exposure fame and now big speaking fees.
    5.The media were well sold for a long time and no opposing view could get a fair hearing. That may be changing.

  52. @P. Solar,
    Temperature is usually the dominant control of solubility at atmospheric pressures, since those change so minutely.

    On the other side, partial pressures play a role for solubility that’s roughly linear–double the partial pressure of CO2 and you double it’s solubility if temperature stays the same.

    See http://www.elmhurst.edu/~chm/vchembook/images2/174solublegas.gif for temperature solubility at what looks like standard pressure versus http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/1940/jacsat.1940.62.issue-4/ja01861a033/production/ja01861a033.fp.png_v03 a range of solubilities at many temperatures and pressures (pressures start at 25 atm for CO2, but it lets you see the behavior).

    Now remember, around the P/T barrier the CO2 went from 3000 to 4000 ppm, not a very large increase in pressure! Hence, the solubility would be negligibly affected by that pressure change (remember, roughly linear).

  53. @Doug Proctor

    An important thing to note, is that biological processes do not necessarily follow simple inorganic chemistry. When the apatite is laid down, it starts as a proteinaceous material, not simply a mineral. The proteins stabilize and deposit the mineral in a controlled chemical way, so that pH of the local environment is also controlled by the proteinaceous mix. Alternate reaction pathways to precipitate the mineral can also be promoted by the proteins and their degradation steps. This is why simply changing the pH of the water the organism is in does not apparently impact the ability to calcify for realistic pH ranges to the same degree as could hypothetically be expected for simple inorganic chemistry.

    The biggest effects pH has on organisms, especially in the very small rages of pH changes we’re talking about for the oceans, are changes in the gene expression patterns. Such pH controlled gene expressions are part of how growth plates work in us humans for depositing and growing the bones.

  54. What were the measured CO2 proxies for the P-T ?
    Were they higher than the mid eocene warm period?
    “pCO2 values were between 600 and 1600 ppmv just before the MECO, which is in line with previous estimates of middle Eocene pCO2 values using the same proxy (14), and rose to between 6400 and 15,000 ppmv during the MECO”

    http://www.sciencemag.org/content/330/6005/819.full?sid=b70ee9f1-229e-4c84-9310-c37cca68a27f

    Science 5 November 2010:
    Vol. 330 no. 6005 pp. 819-821
    DOI: 10.1126/science.1193654
    If the mid-eocene, which is clearly not a mass extinction event, provides a safe maximum CO2 of ~10,000 PPM CO2, the P-T CO2 needs to be much higher, or CO2 is not the main driver of the P-T extinction.

  55. @the fritz says:
    March 7, 2012 at 4:27 am
    Your English is better than my French. Many believe the iridium came from the meteor itself.
    Nombreux sont ceux qui croient que l’usage de l’iridium provenaient de la meteor lui-même

  56. “The change GCR flux due to the solar system moving into the region between the galactic arms, would have taken millions of years. Both coming out and going back in. Plenty of time for life to adapt.”

    MarkW, you are missing the forest for the trees. The geologic time record of ocean temperatures are averaged over thousands of solar cycles and scores of glaciations. The six or seven degree C *ocean* temperature differences from peak snowball earth to peak hothouse earth ocean temps are merely the dance floor for the Solar Samba and the Milankovich Mambo to take to new heights and new lows of atmospheric temperatures.

    The *oceans* were, on average, six or seven degrees warmer during the entire period of the Great Warming, over many millions of years. Add all the variations due to solar cycles, orbital dynamics, vulcanism and chaos, and the air temperatures did what they did.

    This effect can’t just be ignored because the average background flux, before solar modulation, is slowly varying. It takes time for a minor variation in average cloud condensation nuclei numbers to raise the world’s ocean temperatures by 6C and, eyeballing SV03, it would seem to be about an 80 million year process to complete to the limit of the GCR’s effect on climate.

  57. These ‘acid trips’ just keep on going.
    I was given to understand that surface seawaters are supersaturated in carbonates, and that was how exoskeletons grow by catalytic precipitation. Anybody? So calcites, aragonites etc. won’t dissolve because they are actually precipitating [very slowly]. I doubt that could change much in tropical locations where coral grows, because CO2 is probably not dissolving significantly at these locations. Much more dissolves in the colder oceans. And at these pH values it’s also not just thermodynamics that are pointing in the wrong direction, but kinetics too.

    Yes, rainwater, I think, can get below pH 5 with atmospheric CO2. That’s how the lime-water-goes-clear-again-if-you-bubble-lots-more-CO2-through-it-at-school experiment works if you are patient enough. Isn’t going to happen in the oceans. Didn’t limestone and chalk deposits actually form by precipitation in warm oceans? So do carbonates dissolve in the colder oceans where coral doesn’t grow, but more CO2 dissolves? Who cares. But the last time I checked, the White Cliffs of Dover were still there in the English Channel.
    .

  58. This got me thinking about clams, and acid rain… That led to this article:

    http://chiefio.wordpress.com/2012/03/08/clams-do-fine-in-acid-water/

    You will find the Asian Freshwater Clam in the USA with a range that includes areas down to about 4.3 pH. I think that pretty much shows that a tiny bit less alkaline ocean, or even one that actually DID cross to the acid side of 6.x pH still has a long ways to go before clam shells are an issue… Crayfish too (so their cousins the lobsters and crabs ought to do fine…)

  59. The likely cause of the >95% extinction of marine organisms at the PT boundary (more acute than the extinction of terrestrial animals) was anoxia in the oceans – a large scale loss of oxygen.

    Something to do with ocean circulation brought this about. THC might have broken down.

    The CO2 and calcification thing is a total red herring (a politically mandated one) – as has been argued by several here, 3-4000 ppm CO2 is not a threat to calcified organisms that evolved in the Cambrian-Ordovician when CO2 levels were 5-10,000 ppm.

    It is truly pathetic to see the research community manackled to the narrow dogma that nothing in climate and geology is explainable except by CO2.

  60. “It is truly pathetic to see the research community manackled to the narrow dogma that nothing in climate and geology is explainable except by CO2.” – phlogiston

    Bringing that back to my hobbyhorse, geochemist Jan Viezer is on the record as stating he was considering halting his line of research in the oxygen isotope temperature proxy because it wasn’t matching the CO2 record which was presumed to be reasonably well correlated with temps, or anything else he ccould find. Then he got the email from astrophysicist Nir Shaviv with a possible match…

    It takes time for an established paradigm to fade away and CO2 is the chemical du jour. The Triassic, when we (as mammals) evolved, had an average CO2 close to 2000ppm, and we’ll run out of economical fossil fuels long before we get there.

  61. gloccamorra says:
    March 7, 2012 at 8:56 am

    Could a perpendicular meteor strike create a shock wave that triggered the traps? Then you would have two consecutive events, explaining the double spike and extended period of extinction. I’ve suspected the Scotia Plate near the Falklands, since it was near the southern tips of South America and Africa, and the upwelling from a nearly perpendicular strike could explain the deposits of heavy metals in South Africa. Whether a meteor strike could trigger the traps halfway around the world at a later date, I’ll leave up to experts to debunk.

    If it was exactly halfway (i.e., on the mirror lat/long co-ordinates) it would be quite likely to. The globe would “lens” the shock waves and produce an impact from below at a significant fraction of the original impact from above.

Comments are closed.