Oxygen Increase Caused Mammals To Triumph

[phantom power]

Notice that the peak oxygen was 23%, 2 percent higher than today. Their theory about the decrease is some world-wide forest fires around 10 million years ago. (on edit) That would be a nice example of negative feedback. As oxygen concentration rises, things burn more easily.

NEW BRUNSWICK/PISCATAWAY, N.J. – The first, high resolution continuous record of oxygen concentration in the earth's atmosphere shows that a sharp rise in oxygen about 50 million years ago gave mammals the evolutionary boost they needed to dominate the planet, according to Paul Falkowski, Rutgers professor of marine science and lead author of a paper published Sept. 30 in the journal Science.

From a steady 10 percent – the level at which dinosaurs flourished – the oxygen percentage rose to 17 percent 50 million years ago and then to 23 percent by 40 million years ago.

"In the fossil record, we see that see that this rise in oxygen content corresponds exactly to a really rapid rise of large, placental mammals," Falkowski says. "The more oxygen, the bigger the mammals. We argue that the rise in oxygen content allowed mammals to become very, very large – mammals like 12-foot-tall sloths and huge saber-toothed cats. They paved the way for all subsequent large mammals, including ourselves."

There were placental mammals on Earth at the time of the great extinction of dinosaurs about 65 million years ago, Falkowski says. They were, however, tiny, limited creatures; the extinction event itself, while eliminating the dinosaurs, did little to further the mammalian domination of the planet. It was the subsequent spreading of shallow seas, the increase in plant life – and photosynthesis – in addition to the consequent increase in oxygen content that gave the mammals the boost they needed, according to Falkowski.

http://www.sciencedaily.com/releases/2005/10/051003080102.htm

[bemildred]

1. Why forestfires?

Why not all those oxygen greedy life forms
sucking it down and breeding like mad? Maybe
we are past "peak oxygen" and it's all downhill
from here?

[phantom power]

2. I assume they found evidence of forest fires. Just assuming away...

I'm sure there's no reason it couldn't be both. And let's not forget the very large fungus population, which is also a oxygen sink.

It's pretty interesting to think that the oxygen level was half the modern level, for so long. Climate conditions we take for granted have varied quite a lot over geologic history. Sort of emphasizes how much thing could change in the future. From our standpoint, not in a good way.

[bemildred]

3. Sounds rather deus ex machina to me.

If there were giant 10 million year old ash beds maybe.

On the other hand, you would EXPECT an equilibrium
process to occur with the new high-oxygen lifeforms and
the atmospheric oxygen level, especially the ones that
eat plants.

That is an interesting idea about the fungi. I wonder if
the oxygen rise led to a rise in the global protoplasmic
mass, and if so how much?

I do agree that climate change does not get the attention
it deserves in the evolution of life. Were all those giant
mammals dependent on the extra oxygen?

Worry worry worry.

[macllyr]

4. Oxygen levels reached 35-36 % during the paleozoic

High oxygen levels allowed large body-size insects to "breath" through their longer trachea-like tubes (which replace lung and alveoli in insects).

"there was much more oxygen in the atmosphere 300 million years ago than there is today. During this period, the oxygen concentration in the air reached 35 percent, almost double the present level of 21 percent. Oxygen concentration stayed high for about 100 million years, then dropped precipitously to about 15 percent."

researchmag.asu.edu/stories/bugs.html


However, it is not sure (impossible to demonstrate !) that the paleozoic oxygen pulse was the unique cause for the development of giant insects.

Mac L'lyr

[NNadir]

5. In modern times it does seem that we're starved for oxygen.

This would account for some of the thinking we see these days.

[Johonny]

6. I don't know

Mammals were in good shape only 5 million years after the Dinosaurs went bye bye. So I can't see how oxygen levels had a lot to do with it.

[phantom power]

7. They seem to be referring specifically to large mammals

I recently read Loren Eisley's "Immense Journey", and he had an essay describing another such event: the appearance of flowers and seeds. His take was that the availability of concentrated energy in seeds allowed higher-wattage animals to flourish, as well as higher-wattage brains.

More oxygen, higher-octane fuel.

[Johonny]

8. Mammals

started getting big soon after the Dinosaurs left town. They also tend to get bigger during the ice ages. Because bigger bodies retain heat easier. There is at least some evidence that when O2 levels went down mammals simply employed larger lungs. Birds and Dinos went a different route by using internal air sacs.

[NickB79]

9. Dinosaurs flourished on only 10% O2?

That doesn't jibe with theories of at least some dinosaurs being warm-blooded and active, though. And even very large dinosaurs migrated large distances, from fossilized footprint evidence of herds moving from area to area to graze. A metabolism needed for these migrations would have required copious amounts of O2, no?

I'm baffled by the idea that even a cold-blooded 50-ton Brachiosaur, or a 75 to 90-ton Seismosaur, could have done more than stand at only 10% O2.

[Ediacara]

10. This is a little screwy

Mesozoic and especially Paleozoic O₂ levels are known to have been substantially higher than anything in the Cenozoic. I have no idea where they are getting the "dinosaurs flourished in 10% O₂" figure...

[bemildred]

11. Says it's from Carbon13 levels in mud on the seabed. nt