Exploring abrupt climate change induced by comets and asteroids during human history

Another requiem: Holiday-Meltzer doth protest too much

4 Responses

  1. The Daulton Gang is at it again.

    They are kibitzing again. Instead of doing their own science, they opine about others’ work. AGAIN.

    In this paper, in the section titled “Cratering and Comet Physics”, here are the starts to its paragraphs:

    The YDIH impact mechanism has variously been described as an airburst, a cluster of airbursts, an ice sheet impact,multiple continent-spanning impacts (Firestone et al., 2007;Boslough et al., 2012) and ‘a swarm of comets or carbonaceous chondrites [that] produced multiple air shocks and possible surface impact’ (Kennett et al., 2009b, p. 94).

    Firestone et al. (2007) estimate the impactor size by assuming that it had effects over the entire continent.

    Wittke et al. (2013) provide a ‘Preliminary Impact Model’that diverges significantly from the original of Firestone et al.(2007), but still lacks any physics-based argument.”

    Wittke et al. (2013, E2096) propose that fragments of theYDB impactor entered Earth’s atmosphere, fragmented evenfurther and yielded ‘multiple atmospheric airbursts that eachproduced shock fronts’.

    Wittke et al. (2013, E2096) also suggest that ‘thermal radiation from the air shocks was intense enough to melt Fe-rich and Si-rich surficial sediments … at >2,200 ˚C’, a temperature only briefly exceeded in an air shock over a small area near the ablating impactor as it traverses the atmosphere (Nemtchinov, 1995).

    Many of the YDIH papers appeal to airbursts as amechanism by which surface materials can be combusted ormelted by a non-crater-forming impact.

    First of all, notice that NONE of this addresses ANY orginal work by Holliday et al. In reading each paragraph, the clear understanding is that Holliday is drawing no the work of the YDIH team and other papers, but at no point does Boslough get in and show HIS OWN work contradicting ANYTHING that the YDIH papers has stated as fact.

    This is science by Internet, sitting behind a desk.

    Now THIS is the section that is supposed to rip the YDIH a new anal fissure on the grounds of physics.

    As they stated in the Abstract, “The basic physics in the YDIH is not in accord with the physics of impacts nor the basic laws of physics.”

    One would expect this to get VERY precise, very particular – as in, hypothetically, “Wittke did this, and I ran experiments that show this falsifying evidence. Therefore Wittke was wrong on this, because of X, Y, and Z.”

    I mean physics as ALL about NUMBERS – forces, masses, momentums, etc.

    They MENTION Boslough (2012), but don’t they have anything NEW to add to the discussion? They mention that paper in every paper, but they don’t show any new evidence.

    The following “physics” passage is their usual shameless plug for Boslough’s LDG papers, but it doesn’t SAY anything NEW in this paper. It is all re-hash. He is Johnny oOne Note, as we used to say. Where is the NE evidence?

    How do they get away with papers that don’t even have anything new in them?

    Wu et al. (2013)propagated misunderstandings of airburst physics by citing
    Bunch et al. (2012) instead of the original publications which used physics-based models to suggest that layered tektites and Libyan Desert Glass are products of airbursts (Boslough, 1996; Boslough and Crawford, 2008).

    And then there is THIS, “Which I swear is taken word-for-word from earlier papers:

    The airbursts proposed by Bunch et al. (2012) are not consistent with
    the physics of either published mechanism.

    Right, but at the same time, Boslough’s work is all models, NOT REAL WORLD, not empirical evidence. I would put up (YDIH team’s) Peter Schultz’s hyper-velocity experiments against Boslough’s models any day.

    FOLKS, if there is ONE field that is supposed to be about real world and nothing but real world it is non-cosmological physics. Hell, even particle physicists actually do REAL experiments.

    Does Boslough have ANY real experiments? Or are they all cyberspace models?

    * * *

    OKAY, evidently that is all the “physics” in the paper. WOW, a lot of nothing.

    After the buildup in the Abstract, I was expecting SOMETHING tangible, not just a bunch of vague “Your physics sucks!” claims.

    * * *

    Note: I will attempt to comment on each section of the skeptical paper this week.

  2. BTW, the Daulton Gang talks almost exclusively about airbursts.

    As far as I know, no one involved in the YDIH has declared that an airburst “did it, 100%.”

    The Daulton Gang seems fixated on airburts. One is tempted to assign that blame to Boslough, from whom I’ve NEVER heard one word about actual impacts.

    After the Chelyabinsk airburst, I have revised my opinion about airburts, and I don’t think they would have been sufficient. I think that even a very low-angle (radiating infra-red along its path) and then a low altitude airburst just seems to waste its energy.

    Maybe Boslough’s 10-foot-altitude airburst might have been sufficient, because it is damned near an impact anyway. But at hyper-velocity an object isn’t at that height for more than a millisecond or two, and if an object gets that close to the surface, IMHO, it is going to impact, not airburst.

    I think it is wishful thinking to believe that a magic wand is going to get the object down that low and then, instead of impacting, it airbursts.

    I also think that no 4-km object is going to airburst before impacting. I am certain that the unit stresses (pressure) from the resistance of the air is basically the same for 4-km and for 0.1-km objects – and that a much larger object simply cannot ablate enough material in a 30 or 50 second flight in the atmosphere to weaken the body enough to airburst. I could be wrong on that, but my engineering spidey-sense tells me I am not.

    Chelyabinsk had to get down to about 2-5 meters across before it disintegrated and flared. The finally size that hit the lake was only about 1 meter, from an original 17 meters (about 0.2% of the original object). In my thinking, a 4-km object on the same flight path will lose essentially the same amount of mass to ablation as the 17-meter one did. But that much mass burn-off from a 4-km asteroid still leaves 99%, not 0.2% to disintegrate.

    I am not sure about whether it/the object(s) would have been cometary or asteroidal, but I think there were one or more impacts, with a good chance that any other(s) – non-North-American one(s) – were ocean impact(s). My bet would be on asteroids, though.

  3. David –

    I’d seen that, too. But they are drawing conclusions that are not warranted by their paltry number of tusks.

    There are tens of thousands of tusks out in the world. Why are these people only sampling 15 tusks and thinking that that can tell them anything?

    In addition, their assumptions about the weaning age is bull. They are assuming that to be true, and they base it on basically their interpretations, not on what was.

    Add to that the fact that Grayson and Meltzer and Surovell (among others) have long since shot down the Overkill Theory:

    http://faculty.washington.edu/grayson/jwp02.pdfClovis Hunting and Large Mammal Extinction: A Critical Review of the Evidence – Grayson and Meltzer (2002)

    http://www.uwyo.edu/nmwhomepage/pdfs/qi%202008.pdfHow many elephant kills are 14? Clovis mammoth and mastodon kills in context – Surovell and Waguespack (2007)

    The first argues that CHarles C Martin was not only WRONG about Overkill, but that there is essentially almost NO EVIDENCE to support it. They even accuse the followers of Overkill of making an almost religious thing out of it. They also point out that NOT ONE other megafauna that went extinct at the same time has had a kill site connected with it. ZERO.

    They point out that though there are many sites that CLAIM to be kill sites, and they go through them one by one and show why the claims for most of those sites don’t really hold up under scrutiny.

    A very pertinent paragraph:

    In all cases, the extinctions that occurred on islands after prehistoric human colonization are attributed, even by Martin (e.g., Martin, 1984), to a complex set of anthropogenic alterations to the landscape. In no case has the extinction of any island vertebrate shown to have been the result of hunting alone, yet it is only hunting that Martin targets as the cause of the North American continental extinctions. We also note that there is no evidence for widespread human-caused landscape alteration at the time of the Clovis arrival—no massive burning, no rats, no pigs, no chickens, and, although they might have been present(Walker, 1982), no secure evidence for dogs. Finally, the geographic conditions that make island faunas especially vulnerable to extinctions are simply irrelevant to a continent the size of North America.

    The second argues that the few (14 – pointed out by Metzler and Grayson) mammoth/mastodon Clovis kill sites is inadequate to support an overkill theory.

    Now, if Overkill is dead, WHY are people still writing about it as if it is real? Because they simply don’t KNOW about these papers and the facts that are laid out in them.

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