[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Oxygen level in Mesozoic
Agreed that this is an enticing subject, and crucial to our understanding
of the workings of Cretaceous ecosystems. More fuel for the fire also
includes confounding factors for which we still little constraining
evidence but lots of tantalizing possibilities, such as the incidence of
storms, alternate and potentially enormous nitrogen sources, changes in
insolation and other physical parameters, weathering uptake of O and
others... even if we knew that O2 pushed past 30% we are ignorant of the
composition of the rest of the atmosphere! Even a simplified high O2 -
high CO2 system has interesting, unexpected consequences on primary
productivity and metabolism, as recent experimental results have shown. --
Lots of factors to consider, so I would not blow up the atmosphere quite
yet [nor even be sure that this combustion limit applies to the past]. But
would not be surprised to find the dynamics were rather different for our
dear vertebrated friends.
On the side: Ralph Taggart has had interesting things to say about
incidence of fire/charcoal as an O2 proxy, I believe... and R Berner and
his students have done much to improve/finesse their models in recent
papers, reaching oxygen as well as the carbon cycle.
Jeffrey Alan Bartlett
Graduate Student in Paleoecology
Assistant to the Director
Center for the Exploration of the Dinosaurian World
North Carolina State University | North Carolina State Museum of Natural
Box 8208, Department of Marine, Earth and Atmospheric Sciences
Raleigh, North Carolina 27695-8208
Allan Edels wrote:
> Jim (et al):
> We've had this discussion before on list (AND I QUOTE MY REPLY TO YOU
> [Jim] THEN  :-) ):
> " I guess that 35% would be the upper limit, since any
> references I've
> ever seen regarding potentially higher Oxygen levels all use
> that as the
> highest level (I know - pure speculation).
> Of course, the "spontaneous combustion of the biosphere" is
> speculation (since there is no known occurrence of it). It
> reminds me of the
> fear that some of the Manhattan project scientists had, namely
> that the
> detonation of the Atomic Bomb would cause a chain reaction
> leading to the
> entire atmosphere combusting. They still exploded it
> Quoting from The Journal of Experimental Biology 201, 1043?1050 (1998):
> "ATMOSPHERIC OXYGEN, GIANT PALEOZOIC INSECTS AND THE EVOLUTION OF AERIAL
> LOCOMOTOR PERFORMANCE" ROBERT DUDLEY, Department of Zoology, University
> of Texas, Austin, TX 78712, USA and Smithsonian Tropical Research
> Institute, PO Box 2072, Balboa, Republic of Panama;
> e-mail: firstname.lastname@example.org ; Published on WWW 24 March 1998.
> "Concomitant with this reduction in carbon dioxide
> concentration, the oxygen concentration of the late Paleozoic
> atmosphere may have risen to as high as 35 % (Berner and
> Canfield, 1989; see Fig. 1), a remarkable value compared with
> the 20.9 % of the contemporary atmosphere. This elevation of
> oxygen partial pressure occurred against the background of a
> constant nitrogen partial pressure (Hart, 1978; Holland, 1984),
> yielding an increased total pressure of the atmosphere.
> Atmospheric oxygen concentrations are unlikely to have
> exceeded 35 %, as this value represents an approximate
> threshold for spontaneous combustion of the biosphere (Watson
> et al. 1978; Kump, 1989). "
> You [Jim] had referred to this article back in 1998.
> Even though the data from amber is questionable, the speculations are
> still enticing.
> Allan Edels
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org] On Behalf
> Of James R. Cunningham
> Sent: Monday, August 05, 2002 11:51 PM
> To: edels@msn.Com; email@example.com
> Subject: Re: Oxygen level in Mesozoic - LONG
> Isn't 35% about the fraction at which spontaneous combustion of the
> biosphere would be expected?
> Allan Edels wrote:
> > " Hengst and others (1993, 1996) demonstrated that a large long
> > necked sauropod such as the Tithonian _Apatosaurus_ required an oxygen
> > content
> > in the atmosphere of about 35% to function at any level above a very
> > walk, slower than the rates deducted from trackways.