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Re: Mystery of Mass Extinctions Is No Longer Murky



> 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.