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

Re: extinction



> Dear Phil, your suggestion on use of falsification (albeit on
> stratigraphy) in K-T science really struck close to home.
>
> The K-T impact versus volcanism debate began at the May 1981 K-TEC II
> meeting in Ottawa, Canada, when I first encountered the Alvarez
> impact team. At that time, the K-T iridium was the sole basis for a
> K-T impact event.
>
> [...]
>
> To make a long story short, I felt that for Alvarez to continue his
> claim that the K-T iridium was "proof" that an impact event had
> triggered the K-T extinctions, he would have to falsify my argument
> that the Deccan Traps might have been the source of the iridium.

Well then. You were fully right (as far as I can judge events a year before
my birth), and meanwhile the work has been done -- Deccan basalt has a
negative Ir anomaly, not a positive one, so it's difficult to see how it
might have been the source of that stuff elsewhere.

Those platinum nuggets are interesting, though!!! If the Ir is in them -- 
and that wouldn't be surprising at all --, then "diffusion" can only have
happened via bioturbation, if I'm not overlooking something big here.

"_Chemical properties:_ Iridium is the chemically most inert of all metals,
it can be attacked by no acid, but can be dissolved at 150 °C in
hydrochloric acid containing sodium chloride, also in molten sodium chloride
and [sodium] cyanide."

But:

"_Iridium compounds:_ The _iridium(IV) oxide_, IrO2, is formed in heating
iridium dust in the presence of air, it is a black, tetragonally crystalline
substance."

Ref: Bertelsmann Lexikon Chemie. Grundlagen, chemische Elemente -- 
Organische Chemie -- Grundstoffe und Verfahren, Bertelsmann Lexikon 1995, p.
228, my translation

Sounds like the Ir delivered into the air by an impact would immediately
burn down and reach the ground as its dioxide. I've done a google search on
"IrO2":
        According to http://www.finishing.com/240/86.html it isn't soluble
in water, but see below. An acid H2IrCl6 exists in any case, and is
water-soluble
http://www.arofe.army.mil/Conferences/Recent_Abstract/200th_Meeting/symposia/f1/0829.pdf,
http://www.arofe.army.mil/Conferences/Recent_Abstract/200th_Meeting/symposia/m1/1337.pdf;
the impact must have vaporized loads of seawater, so the presence of
chlorine atoms/ions in the fireball which also contained the iridium is
expected.
        The last of the 3,480 results I've checked out is
http://www.pse.pbf.hr/hrvatski/elementi/ir/spojevi.html. Problem is, I don't
speak Serbocroatian, just some Russian... but this page seems to describe a
reaction where Ir is oxidized to IrO2 by _potassium nitrate_ without drastic
conditions. "Chemically most inert of all metals"? Not in this respect!!!
The next line shows what happens when IrO2 is treated with hydrochloric
acid: the water-soluble acid mentioned above comes out. Further down Ir(OH)4
is mentioned; I wonder if this is water-soluble, too.

In short... diffusion of Ir through waterlogged sediments doesn't seem
impossible to me.