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Re: Mystery of Mass Extinctions Is No Longer Murky



Two points in reference to the Gradually Declining Air Mass (GDAM) hypothesis; 

1) to my knowledge, no N2 analysis of crust has been done away from mid-ocean 
rift zones. Also, N analysis of ocean crust/sediments is deliberately done in 
such a way as to exclude N2 of atmospheric origin. In other words, we have NO 
IDEA how much N2 is subducted over time. This is somewhat incredible, but true, 
as far as I have been able to determine...

2) considerably less seriously, but logically, GDAM creates the opportunity to 
speculate that the reason avian dinosaurs are still w/ us, and non-avians are 
not, is that non-avian dinos, unlike birds, did not have the ability to adjust 
the porosity of their eggs to changing (ie, declining) atmospheric pressure. 
This is a novel and new dino extinction mechanism... }:D

Don

--- On Sat, 7/5/08, don ohmes <d_ohmes@yahoo.com> wrote:

> From: don ohmes <d_ohmes@yahoo.com>
> Subject: Re: Mystery of Mass Extinctions Is No Longer Murky
> To: dinosaur@usc.edu
> Date: Saturday, July 5, 2008, 2:54 PM
> > From: David Marjanovic <david.marjanovic@gmx.at>
> > Subject: Re: Mystery of Mass Extinctions Is No Longer
> Murky
> > To: "DML" <dinosaur@usc.edu>
> > Date: Saturday, July 5, 2008, 1:12 PM
>  
> > I don't see what could have happened to the
> chemically
> > extremely stable 
> > nitrogen...
> 
> I do, at least on a qualitative basis.
> 
> 1) seawater that contains N2 circulates through ocean
> crust*. Near 0 C at entry into the crust*, it is subjected
> to heat, pressure, and extreme changes in ph/chemical
> environment* as it circulates through the crust. Abiotic
> fixing has been shown to occur in lab under such
> conditions*. 
> 
> 2) thermophilic N-fixing bacteria (the newest one fixes at
> 98 C) have been found*; my impression is 'everywhere
> we've looked', including deep in crust.
> 
> 3) when subduction occurs (at a rate of 25-35 km^3/a?)*,
> atmospheric N (fixed and physically combined N2) goes down
> w/ the crust. 
> 
> Obviously return mechanisms exist (e.g., slab de-watering,
> back-arc volcanos), but balance is an assumption. The only
> analysis I could find of upwelling crustal waters in a cold
> subduction zone were N-depleted*.
> 
> Here is one test**; chickens adjust egg porosity to nest
> altitude (inverse correlation). Move a laying hen from
> sea-level to 2000m, and the eggs from the respective
> altitudes can differentiated by microscopic examination*.
> 
> In other words, if Cretaceous bird eggs were more porous
> than extant, and by implication, eggs generally, then this
> could support the idea of a higher Cret. atmass. This might
> be fairly accurate if sealevel fossils and nlr's could
> be used. Mound nesting is a potential confounding factor.
> 
> BTW, Roger Seymour found that dino-eggs were very porous
> (4x-100x over extant crocs, IIRC)*.
> 
> M. Javoy states that the N2 mass at end-Archean was as much
> as 3x present.* <== IIRC!!!
> 
> *Yes, there are references. Give me a request, and a week
> or ten days.
> 
> > > You seem to be saying that even a 97% CO2
> atmosphere
> > (er, from some 
> > > totally hypothetical extraterrestrial CO2 source
> for
> > example) wouldn't 
> > > start a runaway on Earth. This aroused my
> curiosity.
> > Is that what you 
> > > meant?
> > 
> > Oh, no. I'm saying we have no chance of getting a
> 97 %
> > CO2 atmosphere unless 
> > we somehow dissolve all limestone in the world. 
> 
> Agreed.
> 
> Don
> 
> > Even the
> > worst-case scenario 
> > (the whole world turns into a tropical paradise) is
> about
> > 0.1 %, and that 
> > would require a massive methane burp that is, judging
> from
> > the last 55 
> > million years, not very probable.