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

Unseen evolution

[Roodvlees]

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.

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.

Re:Terraforming

[gurps_npc]

1) Yes this looks like terraforming - the process of taking a lifeless world and making it suitable for life.

2)That in no way at all implies aliens did it because....

3)All living worlds (hopefully Earth is just one of many) start out as lifeless and then develop life. So all living worlds MUST undergo terraforming.

4) If aliens did it, it would have taken a LOT LESS time then it did. These studies pretty much prove your wrong about aliens doing it.

Whens starting up, a living world's major problem is fuel. It's very hard to eat generic dirt and gasses. So first they need something that can take whatever inorganic raw materials exist and transform it into something more easily digestible. That means taking the atmosphere and turning it into oxygen rich (or whatever other gas the complex life needs) and taking inorganic dirt and turning it into organic fertilizer (i.e. manure). Then more complex life can come along and live off the manure and atmosphere. Then once life fills the planet, multi-celluar life forms can come along and start eating the single celled life forms, which has become good food.

That is how life takes over a world naturally. Intelligence simply speeds up the process, it doesn't change it.