"Oxygen Helped Mammals Grow, Study Finds"

[Allan Edels <edels@msn.com>]

> From Yahoo (around 2:00 PM EDT):

http://news.yahoo.com/s/ap/20050929/ap_on_sc/oxygen_mammals


The text follows:
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WASHINGTON - Mammals, once tiny creatures scampering on the forest floor, 
grew larger as the amount of oxygen in the air increased over millions of 
years, a new study says.

Today mammals, ranging from dogs and cats to elephants, dolphins and people, 
dominate the planet.

It's a success story Paul G. Falkowski of Rutgers University and colleagues 
say was helped by the more than doubling of oxygen in the air over the last 
205 million years. Their findings are published in Friday's issue of the 
journal Science.

The researchers measured samples of material deposited on the seafloor going 
back millions of years. By measuring the amount of carbon-13 in the samples 
they were able to estimate the amount of oxygen in the atmosphere at a 
particular time.

They found that the air contained only about 10 percent oxygen at the time 
of the dinosaurs.

By 50 million years ago the oxygen level had risen to 17 percent and it was 
23 percent 40 million years ago, they reported. Currently the air contains 
about 21 percent oxygen.

The rise of oxygen "almost certainly contributed to evolution of large 
animals," the researchers reported. The oxygen needs of mammals and birds 
are three to six times as high as reptiles.

The impact of an asteroid or meteorite about 65 million years ago is thought 
to have contributed to the demise of the dinosaurs. Their elimination also 
created an opportunity for the rise of mammals.

There was an increase in small and medium-sized mammals in the first few 
million years after the end of the dinosaurs, the researchers reported. A 
second surge, from medium to large sizes, was seen between 50 million and 40 
million years ago, they reported.

The research was funded by the National Science Foundation.

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My comments:

This goes against earlier (somewhat flawed) studies that showed the O2 
levels were very much higher during the Mid to Late Jurassic.  I have 
suggested that the increased O2 levels enabled (or "eased") the dinos to 
growing larger, since you can generate more energy with more O2, easier.

I'd need to see the details of how amount of C13 in OCEAN deposits 
correlates to O2 levels in the atmosphere.

Oh, well....

Allan Edels