Posted on 10/24/2006 10:21:07 PM PDT by SunkenCiv
Vertebrate creatures first began moving from the world's oceans to land about 415 million years ago, then all but disappeared by 360 million years ago. The fossil record contains few examples of animals with backbones for the next 15 million years, and then suddenly vertebrates show up again, this time for good. The mysterious lull in vertebrate colonization of land is known as Romer's Gap, named for the Yale University paleontologist, Alfred Romer, who first recognized it. But the term has typically been applied only to pre-dinosaur amphibians, and there has been little understanding of why the gap occurred. Now a team of scientists led by University of Washington paleontologist Peter Ward has found a similar gap during the same period among non-marine arthropods, largely insects and spiders, and they believe a precipitous drop in the oxygen content of Earth's atmosphere is responsible... He notes that atmospheric oxygen rose sharply at the end of the Silurian period about 415 million years ago, to reach a level of about 22 percent of the atmosphere, similar to today's oxygen content. But 55 million years later, atmospheric oxygen levels sank to 10 percent to 13 percent. The level remained low for 30 million years – during which Romer's Gap occurred – then shot up again, and vertebrates and arthropods again began moving from the sea to land.
(Excerpt) Read more at eurekalert.org ...
In the book, Ward argues that dinosaurs became the monsters that ruled the Earth for more than 60 million years – and survived mass extinctions that destroyed many other species – because they developed respiratory systems far more efficient than other terrestrial creatures.
Out of Thin Air:
Dinosaurs, Birds, And
Earth's Ancient Atmosphere
by Peter Douglas Ward
I had read somewheres that O2 content might have been as high as 30 percent during the time of the great lizards.
I had an email contact last week with a scientist who studies these things and asked him about dissolved O2 in the oceans. He said that's fairly negligible amount. But water high in the atmosphere gets broken up into Hydrogen (which escapes) and Oxygen which stays behind.
Don't know if there is any reliable estimate of how much. But it's interesting that solar weather can have that kind of effect.
And you mentioned 30 percent.
What can we say about the O2 fluctuations except:
Bush's FaultTM!
Cheers!
:') Oxygen in the oceans is replaced at depth by, hmm, hydrogen sulfide I think, which is (if memory serves) a byproduct of bacterial activity at depth (land and sea). Oxygen is pushed into and out of compounds (such as water and various sugars, both of which are produced in photosynthesis; and CO2 through respiration) by biological activity.
Heh...
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