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RE: Oxygen level in Mesozoic - LONG
I have posted several times on this. Here is one of the most complete
versions, from Dec. 1998 (see the Archives).
RE-POST:
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A specific reference:
"Plate Techtonics and the Radiations/Extinctions of Dinosaurs, the Pele
Hypothesis" by Robert E. Sloan (Dept. of Geology and Geophysics,
University
of Minnesota, Minneapolis, MN 55455), from "DinoFest International:
Proceeding of a Symposium sponsored by Arizona State University"
pp.533-539. This was originally presented at the DinoFest in 1996, and
published for the DinoFest in 1998 (March).
The overall thrust of the paper is that changes in oxygen levels
caused
an extinction of dinosaurs (64%) by the early Cretaceous, with 100%
(excluding birds) at the end of the Cretaceous.
Just a few quotes:
-------
"A few of the arguments that the gas in amber bubbles is really
fossil
air are given here, for the others see Landis and others 1996.
* Gases released from deep and surface bubbles of the same piece of
amber
are the same.
* Gas in primary bubbles in highly fractured amber is the same as
from
unfractured amber from the same locality.
* Primary bubbles must be present to yield air.
* Argon 39 produced by neutron irradiation doesn't leak out in 3
years at
VERY high vacuum.
* All Cretaceous ambers show high oxygen. Miocene and Late Eocene
ambers
are low in oxygen with respect to modern air. Oxygen doesn't leak
through
unfractured amber. Modern resin shows modern air."
-------
"1. A high carbon dioxide generated extinction at the end of the
Jurassic and beginning of the Cretaceous with the introduction of large
amounts of carbon dioxide released from the mantle which triggered the
onset
of the Cretaceous greenhouse and, 2. Falling oxygen levels, in the
presence
of elevated carbon dioxide, cause respiratory stress in the exact time
interval when metabolic needs were increasing because of falling global
temperatures. The second type may have been the ultimate cause for most
of
the terminal Cretaceous extinction."
-------
" 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 slow
walk,
slower than the rates deducted from trackways. Our measured levels of
Narremian and Aptian oxygen are 28% and 29% respectively. It thus is
not
very surprising that our only surviving Aptian sauropods are both small,
and
short-necked, clearly adaptations to these low Early Cretaceous oxygen
levels.
THE LATE CRETACEOUS DINOSAUR RADIATION
There are four major factors involved in the Late Cretaceous
radiation
of dinosaurs, all are important. The first is the breakup of Pangea
documented in Figure 1, which permitted the development of endemic
faunas.
The second was the great increase in carbon dioxide and oxygen in the
atmosphere (to 35%), the former favored plant production and diversity,
the
latter permitted an increase in dinosaur size. The third was the
Angiosperm
radiation which greatly increased the food supply. Lastly, the
superplumes
and continental breakup caused a high sea level, and more importantly a
great variation in sea level. ..."
------
"* The increased Carbon Dioxide (up to 6 times the present value)
caused
the Cretaceous Greenhouse effect, and major global warming."
------
" WHY DID DINOSAURS AND NOT MAMMALS GO EXTINCT?
Hengst has shown that Dinosaurs could not ventilate their lungs as
easily
as Birds or Mammals (Hengst et al '93, '96). Figure 3 diagrams these
differences.
* Dinosaurs required 40 breaths to fully replace the air in their
lungs.
* Mammals and Birds only require 7 breaths to completely replace the
air
in their lungs.
* Large Dinosaurs required elevated levels of O2 in the air to
diversify."
-------
Some additional notes:
The paper indicates that the O2 level during the Permian was 14%,
35%
during the Pennsylvanian (and most of the Cretaceous), and is currently
21%.
Barremian 130 mya 28%
Aptian 115 mya
29%
Cenomanian 95 mya 35%
Turonian 88 mya
33%
Judith River Formation 75 mya 35%
Basal Hell Creek 70 mya 35%
Hell Creek (Maastrictian) 68 mya 35%
Top-most Hell Creek 65.2 mya 31%
AFTER K/T Boundary 65 mya 29%
Eocene 50 mya
16%
Miocene 20 mya
14%
NOW NOW
21%
Hope this proves useful.
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RE-POST ENDS.
Of course, more recent work indicates that the O2 levels in the
Mesozoic
may have been equal to current levels.
GROSS SPECULATION:
If the higher O2 rates ARE CORRECT, then dinosaurs might have
grown large simply because their muscles would allow them to
lift more (because they are easily replenishing their O2).
END OF GROSS SPECULATION!
Allan Edels
-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf
Of David Marjanovic
Sent: Monday, August 05, 2002 6:41 PM
To: The Dinosaur Mailing List
Subject: Re: Oxygen level in Mezoic
> Maybe big dragonflies were extinctified by
> competition from/predation by pterosaurs or dino-birds; any idea as to
the
> timing of the appearance and disappearance of these groups?
Yes... big dragonflies didn't live to see the Triassic, it seems (I
suspect
the P-Tr mass extinction). Ptero- and dinosaurs probably appeared quite
some
time later, as their oldest fossils are LTr and their closest relatives
MTr.
There once was a short article in New Scientist (maybe I can find it) on
atmospheric oxygen through time. Says 35 % in the Carboniferous and
Permian,
then around the normal 21 % until the mid-Jurassic, then 26 % until the
Eocene, then 21 again. I recall amber being mentioned... is there any
Carboniferous amber? In any case everything is tentative. :-)