Earth's Oxygen History Could Explain "Darwin's Dilemma" In Evolution

TaleSlinger (3080869) writes Scientists following two different lines of evidence have just published research [Here's the abstract to the paywalled Science paper] that may help resolve "Darwin's dilemma," a mystery that plagued the father of evolution until his death more than a century ago. Life appeared when the earth was tens of millions of years old, but evolution didn't go into high gear until the "Cambrian Explosion", nearly a billion years later. The two papers propose complementary theories that help explain this. The first suggests that scientists have long overestimated the amount of oxygen in the earth's atmosphere in the pre-Cambrian era just before the "explosion." The second suggests suggests that very dramatic changes driven by the tectonic breakup of the so-called "supercontinents" of the pre-Cambrian era could have caused an extraordinary leap in oxygen levels of both the ancient oceans and the earth's atmosphere. These two studies fit neatly together, suggesting that a world deprived of oxygen could have changed relatively quickly into an incubator for new life in shallow ponds spread across the continents and fed by waters rich in nutrients. Perhaps that set the stage for the explosion, which may have been five times the evolutionary rate seen today.

Comments

Re:Cause or Contributor?

[Muros]

I think you missed the point there. Low O2 was the norm until the Cambrian explosion. They are suggesting that higher O2 sparked the explosion, as it opened up new ways for plant and animals to metabolize.

Re:Unseen evolution

[lgw]

Or there was plenty of evolution before this 'explosion', but we don't see fossils of that time because the animals had such soft bodies that don't fossilize well.

Sorry, you just don't get that much size happening with anaerobic microbes (I guess it's possible there were larger fungi - we know so little about fungi anyhow), but there's still plenty of complexity in bacteria. There was a vast amount of evolutionary "work" to get from the RNA sea (or however things started) to bacteria, which today are really quite complex and diverse despite being single-celled. But the major milestone was cyanobacteria.

Once cyanobacteria got going, poisoning the air with deadly oxygen, the doom of almost every other species was written. The Oxygen Catastrophe, was the largest extinction event that we're sure happened. From 2.5 to just under 1 billion years ago, they poured Oxygen into the air, but O2 levels didn't rise much - this is the mystery. One theory is tectonic, as mentioned in TFS, another is the "nickel famine": methane reacts with O2, leaving CO2 and water, so if something happened to the methane-producing bacteria (which need nickel as a catalyst) you'd get a sharp rise in O2.

For whatever reason, O2 spiked, nearly every species died, and the slate was wiped clean. On the up side,O2-based metabolisms have so much more energy available, it opened the door to complex multicellular life.