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Re: "Oxygen Helped Mammals Grow, Study Finds"



At 8:55 PM +0000 9/29/05, Phil Bigelow wrote:
>
>Large mass synapsids (active mega endotherms??) existed in the Triassic. 
>And then there are those annoyingly puzzling Triassic red beds (Why are
>there so many of them?  And why are they red?  Excess oxygen???).     I
>don't know how (or if) either phenomenon fits into the discussion, but I
>thought I'd bring them up anyway.
>
>It's frustrating that the authors didn't also do the Triassic numbers.

As I recall, oxygen levels are generally thought to have been low at the time 
of the Permo-Triassic extinction, with one theory for the slow recover in the 
early Triassic being low oxygen levels. Low oxygen would be more credible at 
the start of the Triassic than in the middle when there was widespread 
diversification of archosaurs and the emergence of pterosaurs. 

It's important to remember that there are a number of steps of inference 
between the raw geological data and the calculated paleo-oxygen levels, so 
errors can accumulate in estimates.  
>
>Uhhh...yeah.  That part really freaks my freak.  If we model the system
>using altitude as our test chamber, we find that there isn't a whole
>lotta biologic diversity currently goin' on at 5 km elevation.  Even the
>lichens and the marmots and the alpine firs haven't gone on a speciation
>spree.  Of course it probably has more to do with decreased temperature
>and a lower air pressure than it does with decreased O2 (see next
>paragraph).
>
>The authors' point about calibration with 5 km altitude is only a rough
>analogy. 

That was my analogy, not theirs. To be fair, Science papers are of necessity 
brief, and they couldn't include much explanation, interpretation, or 
supporting evidence in covering this much ground.  

[clipped]>
>Here's another interesting corrolary.  I wonder if the authors considered
>it as they were preparing their manuscript:
>
>If the 10% O2 figure is correct (for SEA LEVEL), then the anoxic altitude
>would have been vastly lower than it is today.  Meaning that even
>moderate elevation mountains in the early Jurassic may have been totally
>devoid of all animal life. (We REALLY need an O2 vs. altitude graph for
>the early Jurassic, using as a starting point a 10% O2 concentration at
>sea level (1 atm).  Is anyone up to the task?).
>
Marine oxygen levels also depend on atmospheric concentrations, so some effect 
should be visible in the ocean. Given the nature of the fossil record, that 
would be easier to see than the effect at high elevations. 


-- 
Jeff Hecht, science & technology writer
jeff@jeffhecht.com
Boston Correspondent: New Scientist magazine
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