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Re: From Science New, and more (long... I did it again...)
My most naïve questions are really just that. I've tried to keep sarcasm out
of this post... honestly. :-) "Get a bigger head" near the end refers to bone.
Original Message by Sean Carroll
Saturday, 9 November 2002 23:17
> How many physicists,
> chemists, botanists, and other scientists have stumbled on something in
> their own field that just happened to relate, time-wise, to the K-T
> extinctions and lost all sense of objectivity in boldly announcing that
> they have 'explained' those extinctions?
Mmm... I can't think of any, actually. I don't know literature well that is
older than I (born 1982), but all I can think of besides Alvarez & Alvarez
1981 are various findings of poisonous trace elements in end-K fossils in
China (diagenesis), pathological eggshells in France (statistically
insignificant)... and the famous regression which may have been rather local
and took 4 Ma. Is it correct that all evidence for the famous K-T climate
cooling is the huge drop in diversity of planktonic forams (which can also be
explained by a Strangelove ocean)?
Er, botanists? Botanists have found an impressive extinction among
that should be considered part of the K-T mass extinction, shouldn't it?
> The only way to explain a phenomenon like mass extinction is to
> understand its pattern throughout natural history, and the only way to
> understand the extinction of dinosaurs is to have a grasp of the greater
> biological, ecological, and geological picture in which dinosaurs lived,
> died and evolved.
Means, if an impact really did it, we can't possibly find out? -- OK, a less
sarcastic-looking answer: add "and astronomical" before "picture", and I
> Understanding the amount of energy released by a
> bolide impact may be enough to let you create an idealised mathematical
> model *suggesting* that such an impact *might hypothetically* have
> contributed to a particular extinction,
I prefer to look at it the other way around, differently from the historical
sequence in which the hypotheses were built:
We have here a mighty big crater in Yucatán. The only known way to make
a thing is a mighty big explosion, how many 1000 times the whole world's
nuclear arsenal at the height of the Cold War was it. The only known way to
trigger such an explosion is the impact of a mighty big rock or snowball.
Hooray, we find extraterrestrial markers that coincide in time with the
crater -- this shows that something came down at the time the crater was
formed. What effects would such an explosion have had? Can be calculated.
There are numbers like "a magnitude 13 earthquake as far away as California",
"km-high waves" and so on, as well as computer simulations about what would
go up in flames, not to mention the smoke, the noxious gases and so much
more. On the whole, we'd expect a catastrophe comparable to several myths on
how the world is going to end. From this, we'd expect a catastrophic mass
extinction. Yeah fine! We find evidence for a catastrophic mass extinction
that coincides with the formation of the crater, we find evidence for huge
tsunami, global forest fires and so on. So the hypothesis _that the crater
was made by an explosion_ is corrobated. Had we _not_ found a catastrophic
mass extinction at that time, and of course there are still a few people who
think that this is the case, the we would be in serious trouble concerning
_how to explain the existence of the Chicxulub crater_. If, of course, a) all
the math were correct, b) all the datings were correct (and the crater didn't
correspond to another big catastrophic mass extinction!), c) we hadn't
overlooked some factors that somehow dampened the effects of the impact, so
while the math were correct as such, it wouldn't describe reality. I can't
think of another possibility.
Those who think impacts are not alone to blame for the K-T mass
should IMNSHO concentrate on c). I can't recall any ideas that address c).
May just show my inadequate knowledge of geology journals... or the fact that
it's half past 11 pm.
> but that hypothesis then has to
> be integrated into the knowledge we already possess about various
> relevant fields: the way that dinosaurs lived, [...]
Will likely tell us something about the details, the selectivity of the
> the historical
> pattern of extinctions throughout geological time,
Which includes finding out if there is a pattern.
> and the observable
> statistical tendencies of evolution in various populations,
I'm not sure if this is enough. I'm not sure if it would be enough to
consider whole ecosystems instead, or if whole biospheres are required (which
would make the whole thing de facto untestable...)
> Too often scientists, seduced by the popularity and grand
> scope of the subject, get tunnel vision and think of just
> one minor aspect as if it were the solution to everything.
Really?!? Most of the few scientists I've seen in person had, and
largely still have, the following attitude: "Yuck. Not only is spectacular,
it is popular. What more _PROOF_ do we need that it is dead wrong, period. --
It is a fashion (bloated by the evil, evil media) that will go away."
> People [...] who come in from a distant field like chemistry
> or astrophysics [...] are inherently at a disadvantage [...] because
> they have learned a different constellation of facts in their field than
> the constellation that is relevant to the subject.
And at the same time, they are at an advantage because they have not learned
the constellation of factoids and other preconceived notions that are
commonplace in the subject in question, whichever that is. Usually the
disadvantage is bigger. Is it always? I doubt this.
> and fail to know a lot of things that *are* relevant, like the
> historical pattern of large and small extinctions throughout the Mesozoic.
Is it really relevant?
> People who are actively studying dinosaurs and specialise in them have
> a far greater chance of having the right toolbox [...] to make a sober,
> unbiased [...] assessment of the bolide-impact
> model in the view of *all* the relevant evidence,
which includes _not just dinosaurs_ but the whole biota of the time in
question. Otherwise we can't test if the extinctions of different groups at
the same time are similarly gradual or not and so on.
> including especially the
> historical and ecological patterns that physical scientists are most
> likely to be completely ignorant about,
Most of ecology, certainly not all of it, is expected to go up in poisonous
smoke after such a big impact... which makes it IMHO rather easy to give the
physicists some credence.
> The statement of physicists that a bolide impact could release
> enough energy to cause extinction,
Not "could". "Had to".
> [...] is enough to put the bolide-impact-as-cause-of-the-K-T-extinctions
> hypothesis on the ballot, as it were, and open to serious investigation.
> It is *NOT* enough to verify the hypothesis
> and make it acceptable for
> use as a 'standard model' without significant challengers. That can only
> be done by bringing to bear biological, ecological, and historical
> evidence that dinosaur scientists have easy access to, but that are
> foreign and unfamiliar to astrophysicists, for example.
And when paleontologists in general then find evidence for a catastrophic
mass extinction, then I think the whole picture fits together. Doesn't prove
it's true, but any alternative picture must fit at least as good. In the
apparent absence of one, respectively my blindness, this is enough to make
the impact hypothesis the standard model, the working hypothesis that I'd
start from if I did paleontological research on the K-T boundary.
> In point of fact, I believe this larger picture renders the
> direct-causation hypothesis rather silly and at best makes bolide
> impacts a minor contributing factor to the K-T and other mass
I'm interested in your evidence. Can I read it somewhere?
> I find it hard to take such a direct causal 'explanation'
> of extinctions seriously when no one has yet produced any evidence
> that I know of that it would be possible for a planet-wide biological
> community to ever exist *without* rare quasiperiodic mass extinction
Wait a minute. Or two. Are you working from the hypothesis, or rather
speculation, that is advocated in the book "Jurassic Park"? "The Science of
Jurassic Park (and The Lost World) or, How to Build a Dinosaur" has, IMHO
rightly, criticized it: it would only work in a world of perfectly adapted
specialists that had ceased evolving! So I don't see any reason to assume
that a biosphere must exist _with_ any self-made catastrophic mass
> why are we accepting an explanation of a phenomenon as
> 'generally accepted truth' when it has not even been established that
> the phenomenon *needs* an explanation?
Because it has not been established that the phenomenon does _not_ need an
explanation; because if we can find an explanation and can not falsify it, we
have established that it _does_ need an explanation; and because it should
hold the other way around, too. We have a mighty big crater, _therefore_ we
expect a mass extinction of the same age. Too bad we found the mass
extinction long before we found the crater. (the "literary we"...)
And because the pattern of extinction and survival, e. g. ammonoids vs.
nautiloids, surface vs. deep sea and so on, fits more and more what is
expected of a big impact.
> [...] several seriously contending
> models for what happened at the end of the Cretaceous,
...what are the others? I have seen several dying in my life so far... are
there any left?
> And among [...]
> (dinosaur scientists) one finds the widest controversy on the topic,
> while among those likely to have tunnel-vision and proprietary interest
> in a particular ad hoc hypothesis (scientists from other fields) one
> finds the more common 'acceptance' of the hypothesis as an 'agreed
Works the other way around, too. Dinosaur scientists are -- check the
archives from mid-late 1994 on -- likely to concentrate on, say, whether the
Hell Creek Fm. supports a catastrophic or gradual mass extinction of a few
species of dinosaurs, or both respectively neither, instead of whether the
whole picture -- dinos, mammals, rudists, forams, plants, trace elements,
extraterrestrial amino acids, soot, everything, and that around the world --
supports any alternative. I really don't think the answer to why most of
dinosaur diversity was eliminated will come from studying dinosaurs.
Proprietary interest in a particular ad hoc hypothesis? Are you
them of... :-X
> I'm hardly untutoured in physics, not that I would say I have a direct
> intuitive feel for bolide impact energies. But I *do* have an intuitive
> feel for the pattern of speciation and extinction throughout the course
> of biological life,
I can't imagine. How does it work?
> [...] the probable continuity in large and small extinction patterns
When I look at probably the same famous curves, I see different sizes of mass
extinctions that clearly stand out from a pretty continuous background. IIRC
class I (P-Tr), class II (K-T, O-S IIRC), class III (Eocene-Oligocene,
Early-Middle Jurassic, lots more), maybe class IV (mid-Miocene or something)
and probably not more, see below.
> [...] is just ramming one's head against a
> brick wall and declaring 'It will fall if only I hit enough individual
> bricks with enough brute force!' Perhaps it would be better to forget
> the physics of impulse and momentum for a moment and look for a
> way to topple the *whole* wall.
Get a bigger head. :-) It's so simple. Get a bolide that is big enough, if
you are already bringing up this picture. It really looks like if that one
was big enough to topple most of the whole biosphere with nothing but
potential & kinetic energy. Of course craters that are "just" a few km in
diameter aren't connected to global or even continent-wide mass extinctions.
There appears to be a threshold. Like there is a threshold for the size of
the pachycephalosaur needed to destroy a wall of given thickness and
material. (Together with the speed. Comets are a lot faster than asteroids,
so they have the same kinetic energy at much lower masses.)
> But they *did* show a group of Japanese tourists, just before the Rex
> eats that tall whiny white dude. In fact, I've read that the one is
> shouting in Japanese, 'I left Tokyo to get AWAY from this!!' ;)
Really? Cool. :-) Too bad that not many more people can have understood this
gag, if it's real, than those who understood why Dr. Evil and Mini-Him are
playing a Bösendorfer piano and not another firm's -- evil is böse in German.