[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: From Science New, and more (long... I did it again...)



Original Message by John Bois Monday, 11. November 2002 03:32 

> > 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.
>
> Again, what kind of "poisonous smoke" was it that allowed some "of
> ecology" to prosper?

I assume that nothing prospered during the acute effects of the impact, when 
the world was acidic and cold at the surface and dark everywhere. The 
survivors later found themselves in the famous empty world practically 
without competitors (which I mean with the inapplicability of much of normal 
ecology) and therefore prospered -- but this phase probably began a 
geologically measurable time later, see below.
        Poisonous smoke? Is what you get when you burn biomass in air as 
opposed to 
pure oxygen. The so-called pyrotoxins may well have contributed to the 
extinction, and maybe they even explain some of the so-called selectivity, 
though the only book in which I've read about different animal groups having 
different sensitivities to pyrotoxins doesn't cite anything on this and 
doesn't give examples or any further explanation.

> You must accept this burden. [...] without accepting the burden of
> demonstrating/making testable hypotheses, etc., etc., why should this
> idea be taken seriously?

A very good fossil record could offer enough evidence to decide this. For 
some places and clades we have such a thing. An example is IIRC Maastricht 
where the rocks are made of, what was it, haptophytes, forams or both, 
sedimentation rates stay constant up to the boundary, drop abruptly and stay 
low for 5000 years or so -- which means that there were few of these 
organisms in that time. I forgot how this date was determined, probably 
through cyclostratigraphy... I should have the pdf lurking somewhere on my 
harddisk. The author was Jan Smit. Not a very new paper, late 80s or early 
90s probably.

> > And when paleontologists in general then find evidence for a catastrophic
> > mass extinction...
>
> As far as I know this is still an open question.  Terrestrially speaking,
> _no_ vertebrates are known to have suffered a
> "catastrophic" extinction.  Even dinosaurs are still in question, no?

"Even" dinosaurs? The rarest vertebrates of their time except champsosaurs 
and sphenodontians (off the top of my head)? The fewer fossils there are, the 
harder it is to tell, isn't it? -- Last I've read are some pages of Lucas: 
Chinese fossil vertebrates, which I found today in the geosciences library. 
There it says that in the Nanxiong basin dinosaurs were laying large 
quantities of eggs even just before the end, no gradual reduction is in 
sight, there is no unconformity and no overlap of dinos and Paleocene mammals 
(among which, just 10 m above the last dinos IIRC, is the world's oldest 
carnivoran). So currently the record there -- the only terrestrial K-T site 
in Asia -- supports catastrophic extinction, but Lucas hopes for a lot more 
fossils to decide.
        Are there any terrestrial vertebrates known to have suffered a gradual 
extinction? Several groups have been suggested, but is there any for which 
this still holds? I can't think of any, but I know much too little about 
fish, and fish leave lots of fossils, compared to dinosaurs at least, so I 
expect something relevant is known.
        If we leave the K-T, several vertebrate extinctions look gradual, such 
as 
that of a lot at the P-Tr, that of rauisuchians and the last procolophonids 
at the Tr-J... but most of these are underresearched.

> > I really don't think the answer to why most of
> > dinosaur diversity was eliminated will come from studying dinosaurs.
>
> This should be on a plaque somewhere.

It is written. In a book -- I forgot which one. Probably Night Comes to the 
Cretaceous. Haven't I seen that phrase in the list archives?