Monday, August 13, 2007

Fascinating Theory May Explain Great Dino-Mysteries

University of Washington Paleontologist, Dr. Peter Ward, has a fascinating new theory on how dinosaurs evolved, got so big and managed to survive as other forms of life were being wiped out around them.

The controversial theory? It revolves around one thing: oxygen.

In his recent book, “
Out of Thin Air,” Ward argues that oxygen levels in the atmosphere have been slowly guiding the evolution of life on Earth. For example, 300 million years ago, oxygen levels in the atmosphere peaked at 31 percent (today we’re around 21 percent). At that time, insects grew to their biggest sizes, according to the fossil record. Insects have very primitive respiratory systems.

But it’s not just insects, (almost) all life seems to have a relationship with oxygen levels.

According to Ward (
who appeared on CBC Radio’s Quirks & Quarks late last year), when you overlay the fossil record with charts showing oxygen levels in the atmosphere, we see the following:
  • Very few new species develop during periods of high oxygen levels
  • When oxygen levels crash, mass-extinctions occur
  • Periods of low oxygen levels (shortly after a crash) correspond with the appearance of new species
What’s going on here? When oxygen levels are high, life is good. Food is plentiful and it’s easy to pull oxygen out of the air. In other words, species don’t have a dire need to improve (evolve) to survive. It’s when oxygen levels crash that things get interesting. Following one such crash, the
    Permian extinction, 96 percent of marine life and 70 percent of land vertebrates were wiped out. And it wasn’t just animals dying off in large numbers; plant life was severely affected to. Across the wasteland, fungus proliferated and ruled the landscape. But within a million years, while oxygen levels were still low, the first dinosaurs appeared.

    It could be that the dinosaurs appeared in the vacuum left by dominant species, wiped out by plummeting oxygen levels. But that probably wouldn’t prepare dinosaurs to live on for another 150 million years, especially when you consider that other forms of life were wiped out during oxygen crashes in that time period. What seems to have given rise to dinosaurs and saw them through the millennia, Ward suggests, was an innovative new respiratory adaptation: air sacks.

    All vertebrates have lungs, but some (namely birds) also have air sacks attached to those lungs. These air sacks allow birds to extract 30 percent more oxygen from the air than you or I. And in areas where oxygen levels are lower than normal (for example, high altitudes), air sacks help birds pull double the amount of oxygen out of the air than humans.

    “Birds have the most superb respiratory system of all vertebrates,” said Ward on Quirks and Quarks. But how do we know dinosaurs had them? It seems dinosaurs had air sacks because of similarities between modern bird skeletons and dinosaur fossils.

    No comments:

    Pound360 Archive

    About Me

    My photo
    I started pound360 to channel my obsession with vitamins, running and the five senses. Eventually, I got bored focusing on all that stuff, so I came back from a one month hiatus in May of 2007 (one year after launching Pound360) and broadened my mumblings here to include all science.