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Re: "Oxygen Helped Mammals Grow, Study Finds"
I had posted some things relating to this idea some time ago
[http://dml.cmnh.org/1998Dec/msg00575.html]
RE-POST FOLLOWS:
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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:
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"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."
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" Hengst and others (1993, 1996) demonstrated that a large long necked
sauropod suchas 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."
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" WHY DID DINOSAURS AND NOT MAMMALS GO EXTINCT?
Hengst has shown that Dinosaurs could not venilate 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."
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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%
Of course, some recent work (using new techniques) indicates that the O2
levels in amber may have been equal to current levels. 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).
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RE-POST ENDS.
Now:
Some more recent work indicates that amber is more porous than previously
thought for some molecules (O2, CO2, CO, N, NOx, N2H2, H2 among others).
Some people have speculated that any O2 above 35% would enable spontaneous
combustion of the atmosphere. (This was also thought would happen when they
tested the first atomic bomb - but they tried it anyway).
I think the percentages shown in this older study are higher than reality,
and you probably should subtract 5-10 percentage points off each of the
numbers shown. (Except for our current percentage).
Allan Edels
From: Tim Williams <twilliams_alpha@hotmail.com>
Reply-To: twilliams_alpha@hotmail.com
To: dinosaur@usc.edu
Subject: Re: "Oxygen Helped Mammals Grow, Study Finds"
Date: Fri, 30 Sep 2005 10:04:36 -0500
Mike Taylor wrote:
On the Internet, no-one knows who you are. How can you tell that I'm
not an algae colony with unusually developed typing skills?
(I'm not really an algae colony, of course. I'm a lobster.)
I'm a slime mold!
David Marjanovic wrote:
One more quote (refs removed):
"Whereas the relatively rapid decline in oxygen at the end-Permian and
early Triassic is suggested to have been a major factor contributing to
the extinction of terrestrial animals (mostly reptiles) at this time, the
rise of oxygen over the ensuing 150 My almost certainly contributed to
evolution of large animals.
This may be a daft question, but I had heard/read that oxygen levels were
relatively high during the Permian. This allowed large flying insects
(_Meganeura_) to thrive during this period, owing to the higher oxygen
tension in the atmosphere. The end-Permian drop in O2 may have contributed
toward their extinction too.
Interesting how the authors use "secular" -- apparently for "long-term".
As in "The data presented here provide evidence of a secular increase in
atmospheric oxygen over the past 205 My that broadly corresponds with three
main aspects of vertebrate evolution, namely endothermy, placentation, and
size."
I think we need to know more about the religious beliefs of marsupials
before we can draw any firm conclusions.
Cheers
Tim