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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.
... evolution didn't go into high gear until the "Cambrian Explosion", ...
I'm not sure I believe that - one could reasonably argue that the growth in complexity from a soup of ribozymes to the first cell, was comparable to the leap from single-celled organisms to multicelled; or possibly far more involved than that. Another major leap was from prokaryotes to eukaryotes, a necessary precondition for (most) multicelled life, it would appear. What happened at the Cambrian explosion was probably just that now the organisms got big and touch enough to leave fossils.
More you read about this, more it looks like terraforming. Sure, it all could have happened by chance, but if I was a spacefaring civilization trying to turn Mars-with-water planet into something more suitable for life this is how I would likely do it.
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.
Thank you, Bradley Manning, Edward Snowden and so many others, for courageously defending humanity, my freedom and more!
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.
Second lack of evidence is not the evidence of lack. Before the Cambrian "explosion" the organisms had not developed bones and shells that would fossilize. It is very hard for soft bodies to fossilize and for the indirect evidence to stick around. There are very few places where the original primordial earth crust still survives without change. Almost the entire seafloor is new. Constantly being melted into the magma in the subduction zones and being reformed in the expansion zones. No evidence of anything would survive that. So it is totally incorrect to say that earth was not teeming with life or that the competition was absent.
Today multi-trillion cell agglomerations are sitting on keyboard and typing follow up responses to pointless postings in slashdot. Many trillion cell colonies of micro organisms live symbiotically with these agglomerations which call themselves human. Trillions of these cells commit suicide promptly when the signal arrives, to be replaced by new copies. They know they are not in the gonad and they will never reproduce. Still they all tick along doing their stuff. The foundations for such a way of life for these cells were laid down before the Cambrian "explosion".
And we become time traveling mind readers and state confidently "Darwin was plagued by the mystery...". Darwin was constantly complaining of so many illnesses he was such a strain on Emma. He had lot more than a mystery plaguing him.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
which may have been five times the evolutionary rate seen today.
Look up epigenetics, and a few other factors, evolution is not slow.
"If any question why we died, Tell them because our fathers lied."
I would love to Evolve...but every time I try, these hunters show up and try to lock me into a mobile arena. It is seriously annoying!
I only look human.
My mother is a halfling and my dad is an ogre, so that makes me an Ogreling
"They are suggesting that higher O2 sparked the explosion"
That sounds logical from the chemists perspective
So did the oxygen simply appear out of nowhere (he asks rhetorically)? Of course not. If it was somehow trapped in the oceans or underground, and then released as postulated by these papers, then one must explain the mechanism that would have dissolved and/or trapped the O2 to start with. What was different about Pre-Cambrian oceans that allowed for more oxygen to be dissolved in it than modern oceans? What caused the release and the change to what we have now? Likewise, what mechanisms in tectonic plates shifting would account for a massive release of oxygen and from where?
I am not saying these hypothesis being presented are incorrect, but they need to be able to explain the before as well as the after.
The Cambrian explosion is more likely explained in terms of genetic software. At some point, a collection of genes evolved that could reliably control and pass on complex growth patterns. Before those existed, multi-cell organisms had very simple forms and limited functionality. Once that morphological operating system was in place, a vast variety of organisms could evolve.
Rather than sparking rapid evolution, maybe the high O2 concentrations led to (or allowed) the development of hard tissue in existing complex organisms. Ocean acidification dissolves the shells of clams, corals, etc. and increased O2 levels could coincide with decreased CO2 levels (probably because the organisms creating all the O2 had to get it from somewhere).
This being Slashdot (and the link being paywalled) I have not bothered to read the linked article. Hell, I've barely bothered to read the summary.
just a ghost in the machine.