The Cambrian Explosion
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05-07-2017, 09:20 AM
RE: The Cambrian Explosion
(05-07-2017 09:17 AM)unfogged Wrote:  Answers in Genesis... Laugh out load

You funny

I'm glad I made you laugh. Laughing is good for health. Smile

The information in ancient libraries came from real minds of real people. The far more complex information in cells came from the far more intelligent mind of God.
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05-07-2017, 09:22 AM
RE: The Cambrian Explosion
(05-07-2017 09:14 AM)theophilus Wrote:  
(05-07-2017 09:07 AM)TheBeardedDude Wrote:  Translation: here is some anti-science religious propaganda from some morons who think they know science better than scientists

We don't claim to know science better; we claim we know history better. Those who deny evolution do so because we accept the first answer.

Well, you don't know history better and are complete imbeciles for thinking otherwise. Please keep your garbage away from those who follow history/science and life generally.

Stuff like this is dangerous, especially when presented to people having a crisis of faith or, in seajays case, worrying about eternal damnation so much it's given him anxiety problems.

Your whole motto of "We don't claim to know science better; we claim we know history better." is so wrong, I don't even know where to begin. Using the scientific method we can distinguish between what is just bullshit stories and FACT. There is NO, and I repeat NO evidence what so ever for a global flood happening, EVER. It did not happen, please understand that. The website you posts, reads like a nervous teenager trying to think of things, "Well...um...It could have been the great flood, you know?". WRONG, it wasn't, because that NEVER happened.

History is full of bullshit, especially in the era's of people themselves being too dense to comprehend what is real and what is make believe, so that's where science comes in to see if these claims actually have any evidence. And guess what, they don't.

So please take your garbage can full of lies, and post it somewhere else please.

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05-07-2017, 09:27 AM
The Cambrian Explosion
(05-07-2017 09:14 AM)theophilus Wrote:  
(05-07-2017 09:07 AM)TheBeardedDude Wrote:  Translation: here is some anti-science religious propaganda from some morons who think they know science better than scientists

We don't claim to know science better; we claim we know history better. There is one historical question that must be answered before we try to understand nature. Was the universe created by God or did it come about entirely as a result of natural processes? The belief that the earth is billions of years old and that life came about by a process of evolution is the result of accepting the second alternative. Those who deny evolution do so because we accept the first answer.

https://clydeherrin.wordpress.com/2014/0...t-science/


That's some extra smelly bullshit.

Geology is the scientific discipline that studies the earth AND its history. Denying basic scientific facts from geology, is anti-science propaganda. And AiG doesn't know history better. It is a religious propaganda organization with an anti-science agenda


Cheers
TheBeardedDude

Being nice is something stupid people do to hedge their bets
-Rick
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05-07-2017, 09:42 AM
RE: The Cambrian Explosion
(05-07-2017 01:55 AM)SeaJay Wrote:  I also posted this on the 'Ex Christian' website.

I hope you believe me by now that I'm not here pushing agendas, I come here looking for answers to questions I have. Not sure if anyone remembers but my story is a complicated one (http://www.thethinkingatheist.com/forum/...-Believe).

I've been reading up on the Cambrian Explosion 543 million years ago, and it's worrying me, quite a bit. Reason being, the science community does not know why the CE took place the way it did. The following is taken from this website:

http://burgess-shale.rom.on.ca/en/scienc...hp#explain

"Why did the Cambrian explosion happen when it did, and why was it such a unique event? While there is no current consensus among scientists, most researchers agree the explosion cannot be ascribed to a single, simple causal mechanism. The potential triggers can be classified in three main categories: environmental, genetic, and ecological. Deciphering the impact of each of these factors remains one of the most important challenges faced by palaeontologists today."

I read about the three main triggers but none of them are convincing and/or believed with any real conviction by the scientific community. :/

This is worrying. I thought the evolutionary fossil record was such that, whilst it never claimed to be 100% undeniably correct, it was a pretty solid explanation for life on earth. I believe to some extent it still is; it definitely shows us 'how' life evolves over time, but this sudden emergence of simple bacterial life forms to hard-shelled complex organisms during the Cambrian Explosion of 543 million years ago is problematic for me because the science community cannot explain it. It's like my faith in science just took a nosedive and suddenly all those things you hear in Christian circles about God exposing the hubris of learned men start flooding back.

Up until this moment, science had the answers to everything I looked for, and in that respect, it gave me answers to questions the Bible proposed. That's a naive statement of mine (to believe science had all the answers), but for me, personally, that was the case.

Now though, in the lack of any real evidence agreed upon by the scientific community, it takes as much faith to believe the Cambrian Explosion was not initiated by God than to believe it might have been. It's almost like 50%-50% odds.

21 So God created the great sea creatures and every living creature that moves, with which the waters swarm, according to their kinds, and every winged bird according to its kind. And God saw that it was good.

Looking at the above verse I'm sat thinking, what if the creation story in the Bible isn't supposed to be read like a science paper, but is just a way to get across to us the knowledge that God created life?

To put it another way, I'm reminded of Galileo's quote: "The Bible shows the way to go to heaven, not the way the heavens go."

Whilst "most researchers agree the explosion cannot be ascribed to a single, simple causal mechanism", and whilst there's evidence of life before the Cambrian Explosion, it is different enough that science can't explain how it got from A to B and that causes me anxiety because now, my leaning is more toward the belief that Christianity is true and that means hell is again a real possibility. That's an overly simplistic way of looking at it, I know some might say I'm just invoking a 'god of the gaps' point of view, but I can't help it. That's how I feel right now.

This is the first time science hasn't had an adequate explanation for me and it's quite worrying. I feel I am on very shaky ground here.

Any suggestions?

Thanks all.

EDIT: Ironically, the best explanation I've read (currently) about the Cambrian Explosion, comes from this Christian website who uphold the theory of Evolution.

http://biologos.org/common-questions/sci...-explosion

Science doesn't owe you anything.

http://evolutionid.wordpress.com/2010/06...explosion/
Kenneth R Miller "Finding Darwin's God" (a molecular biologist / Roman Catholic / PhD from Brown University) has a very complete chapter refuting ID/creationist claims about the Cambrian ("explosion") Period.

Basically, (even though there are NOT), even if there might be some unanswered questions about this period, it's still an argument from ignorance, an argument from personal incredulity, and "plugging in" (some -- any ??) undefined god, is the LAST possible reason one would resort to.

Insufferable know-it-all.Einstein God has a plan for us. Please stop screwing it up with your prayers.
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05-07-2017, 09:50 AM
RE: The Cambrian Explosion
(05-07-2017 08:48 AM)TheBeardedDude Wrote:  The Cambrian Explosion?!
[Image: vJCUaItP2rgBwso3rfaTJzqLQ2TG1S-1N5PlmWM7...fda8e18bc6]

Now that is a subject worth discussing!

The Cambrian Explosion is quit the interesting event and it is indeed a subject where you won't find a ton of consensus among paleontologists about the primary mechanisms driving it. What you will find is a consensus that it isn't a problem for evolution or the history of life and probably also a consensus that the word "explosion" is a huge misnomer that has inadvertently given the impression of an instantaneous appearance of life on Earth. It isn't so.

Some basic facts about the Cambrian Explosion:
1) It occurred over millions of years (maybe 10 million years or more). The beginning of the Cambrian is defined based on the appearance of vertical burrows, which indicate that animal life had evolved a new behavior for burrowing through sediment for food and/or shelter. The faunas of the Cambrian Explosion won't appear for several more million years, but...
2) animal life was already going strong and had been for tens of millions of years. The animals that had been alive from the Ediacaran (and probably back to the Cryogenian) up to the Cambrian were quite weird (the Ediacaran Faunas are very bizarre) and mostly soft-bodied. The soft-bodied nature of animal life meant...
3) most animals up to the early Cambrian would have been extraordinarily difficult to preserve. That is because they are soft-bodied and because...
4) the depositional environments on Earth weren't quite like they are today. The Ediacaran faunas, for instance, are preserved in a way (sometimes called a "death mask") that doesn't really happen again after the Phanerozoic Eon begins (the Eon that starts when the Cambrian starts. The Eon we are currently in). The reason those environments were so different is probably because life wasn't as abundant or diverse as it is today (or during the bulk of the Phanerozoic). Life interacts with its environment and can change the physical and chemical parameters. For instance, organisms burrowing into the sediment can mix it up and help bury organisms and also oxygenate the sediments for organisms to live in (where they can then die and become preserved or leave behind traces). Back to those...
5) trace fossils that define the beginning of the Cambrian. They tell us that the same vermiform organisms alive in the oceans today, were there around the beginning of the Cambrian. Meaning that their ancestors were alive in the Ediacaran. And fossils like Kimberella are similar enough to molluscs that many consider it to be an ancestral mollusc (not everyone is convinced of this because it lacks a radula, but its other characters are very similar to many molluscs). So animals that were primarily soft-bodied were doing just fine before the Cambrian Explosion. That's because...
6) the Cambrian Explosion is primarily about the appearance of hard-bodied organisms in the fossil record (organisms with an exoskeleton mainly). With the beginning of the Cambrian, animal life was becoming more diverse. That increase in diversity meant an increase in predation (for the moment we can also consider grazing organisms to be "predating" another organism too). That selection pressure would have driven an evolutionary arms race between predator (who would have also been subject to predation pressures) and prey. The result was an increase in armor and the development of organs for better finding prey and avoiding predators (like eyes). Why did it take so long for this to happen?
7) Before the Cambrian, the oceans were pretty low diversity and very low in oxygen. The concentration of oxygen is directly proportional to the amount and size of respiring life that can survive in it. So animal life was doing well before the Cambrian Explosion, but it was primarily a low diversity fauna of very small organisms. The smaller the organism and the more soft-bodied it is (coupled with environments that had a low preservation potential), the harder it is to preserve and then find in the rock record. But the signs are there in what fossils we do find, as well as in the geochemical record. In fact...
8) the geochemical record probably tells us the rest of the story. During the Cryogenian the Earth went through 2-3 phases of being covered from pole to equator in ice (land and ocean both covered in ice during the Snowball Earth events). One potential side effect of this would have been the grinding up and mass movement of sediment off of the continents into the ocean. This is hugely important because it would have introduced iron (a primary limiting nutrient in the oceans) and phosphorous (another limiting nutrient and one that can only come from the rock record or the remineralizaton of organic matter in sediments). This introduction of large quantities of nutrients seems to have helped life increase in diversity and complexity (as evidenced by the Ediacaran fauna). This is an important precursor because...
9) it would have helped facilitate a massive change to the global carbon cycle. That is because you'd have a brand new standing crop of biomass. This new abundance of organisms would have helped sequester CO2 from the atmosphere into the biosphere (the living organisms) and the lithosphere (organic matter being buried in sediments). This is hugely important because...
10) sequestering the organic matter prevents it from being oxidized back into CO2. Meaning that the concentration of oxygen in the atmosphere and oceans would have begun to increase as the quantity of living organisms continued to increase. More oxygen in the water and atmosphere would have helped facilitate the evolution of larger bodied organisms. And to add to this...
11) sequestering CO2 as organic matter would have also helped lower the overall temperature of the early Cambrian Earth. The Cryogenian is weird and also quite debatable as to how it happened and how the Earth came out of it. But other than these phases of glaciation, the Proterozoic and early Phanerpzoic Earth were very warm. And warm water doesn't hold as much oxygen (or any dissolved gas) as cooler water. So a cooler global ocean that is less variable, would be more conducive to life. That is because it isn't just necessary that oxygen concentrations are high enough for respiring life, but the concentration of oxygen can't get too low due to the diurnal cycles. Meaning that it doesn't do respiring organisms any good for oxygen concentrations to be good at night when it is cooler, only for the oceans to get too hot during the day (which would cause the oceans to become dysoxic to anoxic in places). And on top of that...
12) most macroinvertebrates can't withstand temperatures in excess of ~34°C for prolonged periods of time. So the oceans becoming more thermally stable would have also benefited the very organisms that will eventually begin to diversify during the Cambrian Explosion. And then on top of all of this...
13) the temperature of the water as well as the concentration of CO2 in it, will effect the solubility of aragonite and calcite (each are CaCO3). These are the two primary minerals used in the exoskeletons of organisms (even for some arthropods they use calcite to reinforce their exoskeletons. That is why the claws of crabs are so tough. And early Arthropods present in the Cambrian used calcite to reinforce their shells too, like trilobites). This change in solubility would have made it easier to produce shells. And shells are much easier to preserve than soft-bodied organsims because the shells and skeletons don't decompose. So as long as they get buried before being destroyed, they should produce a fossil (which could later be dissolved away by groundwater but that could still leave behind a mold or cast or a recrystallized fossil or a permineralized fossil or a fossil with a new mineralogy having precipitated out in its place in a process called replacement).

So what that ultimately means is that the "Explosion" of hard-bodied organisms was likely a consequence of:
1) increased nutrient input into the oceans
2) change in the global carbon cycle due to an increase in standing biomass
3) sequestration of CO2
4) increase in O2
5) reduction in global mean temperatures and stabilization of temperatures
6) increased concentrations of carbonate ions in the water and increased alkalinity facilitating the development of biomineralization in animals


Two additional important points:
1) Weird Cambrian preservation has produced a diversity observed in the fossil record that is very rare. The Burgess Shale and the Chengjiang faunas are both early Cambrian and both have exceptionally well-preserved soft-bodied animals (the latter has the oldest known chordate, our direct ancestor). These extremely rare instances of preservation happen to be in the early Cambrian and if not for them, we wouldn't know about the bulk of the animals preserved. We wouldn't know about the early Chordates nor the priapulid worms nor any of the primarily soft-bodied animals. Meaning that if we didn't have these two fossil localities, the Cambrian Explosion wouldn't look anywhere near as sudden or odd with respect to the fossil record. Basically, we got lucky for those preservation conditions to have existed and even luckier someone found them.

The Burgess Shale, for instance, is quite intriguing. It is a locality up in the Canadian Rockies and is only accessible for a few months out of the year in the summer. In the mid-1800's, it was discovered by accident when a horse kicked over a slab that had a weird fossil on it. The Burgess Shale is part of a turbidite, which is an underwater mass slump deposit that occurs on the edge of a continental shelf. The organisms preserved were alive on the upper portion of the shelf when it became unstable and collapsed, taking all of them with it. They were deposited in the debris flow along the abyssal plain and essentially buried alive. Those organisms were deposited suddenly in a debris flow into an environment with very little to no oxygen. This prevented them from decomposing and left us with fossils that are so well preserved, you can still dissect them. And on top of that, different imaging techniques reveal new details. For instance, x-raying the trilobites reveals the antennae, legs, and gills. These are all structures that are almost never preserved with trilobites during the nearly 300 million years they were around. So the Cambrian Fauna is in part weird and extremely diverse because of pure dumb luck (lucky for us but not so much for them).

2) it was never an "explosion." This is pretty much the same story as the tale of it being called the Big "Bang." It is a misnomer. The fossils of the early Cambrian appear "suddenly" with respect to geology. What that means is that it occurred over millions of years. So it wasn't so much an "explosion" because that implies that the diversification would have been observable to a human within a matter of seconds, minutes, hours, days. That was never what it meant. Cambrian "Explosion" really just meant that there is a point in the rock record where the quantity and diversity of fossils increases rapidly over a short stratigraphic distance.
Great post, thank you for sharing it.

What do you make of the info on this site that suggests the oxygen and glaciation theories are not that convincing. If they're not, a lot of your post after points 7 and 8 seem to be in doubt. Sorry if that sounds like a personal attack it's not meant to be. I'm just struggling with words here.

http://burgess-shale.rom.on.ca/en/scienc...n.php#box7

Oxygen
However, there does not seem to be much variation in oxygen levels across the Ediacaran-Cambrian boundary. Earlier increases might have triggered the evolution of large Ediacaran metazoans prior to the explosion, and a subsequent post-explosion rise in oxygen levels may have allowed animals to adopt more active, energy-intensive lifestyles such as swimming and hunting.

Glaciation
Unfortunately for the hypothesis, the last worldwide glaciation seems to have ended around 635 million years ago - nearly 90 million years before the first signs of the Cambrian explosion in the fossil record (which was followed by another major regional glaciation around 580 million years ago).

“I am so clever that sometimes I don't understand a single word of what I am saying.” ~ Oscar Wilde
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05-07-2017, 10:06 AM
RE: The Cambrian Explosion
(05-07-2017 01:55 AM)SeaJay Wrote:  I've been reading up on the Cambrian Explosion 543 million years ago, and it's worrying me, quite a bit. Reason being, the science community does not know why the CE took place the way it did.
By your logic you should be (yet, apparently aren't) worried about abiogenesis as a hypothesis for how life arose.

Science does not have ALL the answers for EVERYTHING. It's still working on some things: life from non-life, aspects of the Cambrian explosion, the existence and provenance of so-called dark matter, the multiverse, and many other things.

This is not cause for concern, it's exactly what you'd expect. And science (1) refusing to provide certitude it doesn't have and (2) being willing to change its conclusions when new evidence presents itself are features, not bugs.

Your problem isn't the Cambrian Explosion, it's that you are still married to the notion that certainty is a requirement for you to determine whether an epistemology is likely to be correct or not. Evaluation of different epistemological systems (religious faith and science, in this case) is not based on how much certitude they (claim to) provide, or how intuitive they seem, but on what sort of track record they have for predicting and explaining the reality that all humans experience together.

Has religion ever invented or innovated anything, or ever corrected errors in science?

Has science ever invented or innovated anything or ever corrected errors in religion?

Has science ever been forced to change because of religion?

Has religion ever been forced to change because of science?

I rest my case.

All that said, evolution strikes me as a process that reaches tipping points where conditions are very favorable for diversification. This favorability may consist of reaching stable / favorable environmental parameters, and/or, simply achieving a fundamental evolutionary feature that so improves survival rates that natural selection is accelerated. It is unsurprising to me that the pace of natural selection would vary, and that as the environment becomes less volatile and more novel adaptations appear in the gene pool, it would tend to accelerate overall and in spurts.

It took a very long time indeed for multicellular organisms to evolve, but once that happened, it took relatively less time for those multicellular organisms to diversify into what we see today. The Cambrian "explosion" is just a tiny part of that relatively short evolutionary time span and itself took tens of millions of years. So it's not even an "explosion" except in certain relative terms and is also part of a larger "explosion".

Another relevant question to consider: even where sure information is sparse, where has the totality of evolutionary knowledge pointed? That is where less-developed understanding is apt to go, too. It is not apt to suddenly validate magical thinking.
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05-07-2017, 10:06 AM
RE: The Cambrian Explosion
I think "suggests" is a weasel word.
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05-07-2017, 10:56 AM
RE: The Cambrian Explosion
(05-07-2017 09:50 AM)SeaJay Wrote:  
(05-07-2017 08:48 AM)TheBeardedDude Wrote:  The Cambrian Explosion?!
[Image: vJCUaItP2rgBwso3rfaTJzqLQ2TG1S-1N5PlmWM7...fda8e18bc6]

Now that is a subject worth discussing!

The Cambrian Explosion is quit the interesting event and it is indeed a subject where you won't find a ton of consensus among paleontologists about the primary mechanisms driving it. What you will find is a consensus that it isn't a problem for evolution or the history of life and probably also a consensus that the word "explosion" is a huge misnomer that has inadvertently given the impression of an instantaneous appearance of life on Earth. It isn't so.

Some basic facts about the Cambrian Explosion:
1) It occurred over millions of years (maybe 10 million years or more). The beginning of the Cambrian is defined based on the appearance of vertical burrows, which indicate that animal life had evolved a new behavior for burrowing through sediment for food and/or shelter. The faunas of the Cambrian Explosion won't appear for several more million years, but...
2) animal life was already going strong and had been for tens of millions of years. The animals that had been alive from the Ediacaran (and probably back to the Cryogenian) up to the Cambrian were quite weird (the Ediacaran Faunas are very bizarre) and mostly soft-bodied. The soft-bodied nature of animal life meant...
3) most animals up to the early Cambrian would have been extraordinarily difficult to preserve. That is because they are soft-bodied and because...
4) the depositional environments on Earth weren't quite like they are today. The Ediacaran faunas, for instance, are preserved in a way (sometimes called a "death mask") that doesn't really happen again after the Phanerozoic Eon begins (the Eon that starts when the Cambrian starts. The Eon we are currently in). The reason those environments were so different is probably because life wasn't as abundant or diverse as it is today (or during the bulk of the Phanerozoic). Life interacts with its environment and can change the physical and chemical parameters. For instance, organisms burrowing into the sediment can mix it up and help bury organisms and also oxygenate the sediments for organisms to live in (where they can then die and become preserved or leave behind traces). Back to those...
5) trace fossils that define the beginning of the Cambrian. They tell us that the same vermiform organisms alive in the oceans today, were there around the beginning of the Cambrian. Meaning that their ancestors were alive in the Ediacaran. And fossils like Kimberella are similar enough to molluscs that many consider it to be an ancestral mollusc (not everyone is convinced of this because it lacks a radula, but its other characters are very similar to many molluscs). So animals that were primarily soft-bodied were doing just fine before the Cambrian Explosion. That's because...
6) the Cambrian Explosion is primarily about the appearance of hard-bodied organisms in the fossil record (organisms with an exoskeleton mainly). With the beginning of the Cambrian, animal life was becoming more diverse. That increase in diversity meant an increase in predation (for the moment we can also consider grazing organisms to be "predating" another organism too). That selection pressure would have driven an evolutionary arms race between predator (who would have also been subject to predation pressures) and prey. The result was an increase in armor and the development of organs for better finding prey and avoiding predators (like eyes). Why did it take so long for this to happen?
7) Before the Cambrian, the oceans were pretty low diversity and very low in oxygen. The concentration of oxygen is directly proportional to the amount and size of respiring life that can survive in it. So animal life was doing well before the Cambrian Explosion, but it was primarily a low diversity fauna of very small organisms. The smaller the organism and the more soft-bodied it is (coupled with environments that had a low preservation potential), the harder it is to preserve and then find in the rock record. But the signs are there in what fossils we do find, as well as in the geochemical record. In fact...
8) the geochemical record probably tells us the rest of the story. During the Cryogenian the Earth went through 2-3 phases of being covered from pole to equator in ice (land and ocean both covered in ice during the Snowball Earth events). One potential side effect of this would have been the grinding up and mass movement of sediment off of the continents into the ocean. This is hugely important because it would have introduced iron (a primary limiting nutrient in the oceans) and phosphorous (another limiting nutrient and one that can only come from the rock record or the remineralizaton of organic matter in sediments). This introduction of large quantities of nutrients seems to have helped life increase in diversity and complexity (as evidenced by the Ediacaran fauna). This is an important precursor because...
9) it would have helped facilitate a massive change to the global carbon cycle. That is because you'd have a brand new standing crop of biomass. This new abundance of organisms would have helped sequester CO2 from the atmosphere into the biosphere (the living organisms) and the lithosphere (organic matter being buried in sediments). This is hugely important because...
10) sequestering the organic matter prevents it from being oxidized back into CO2. Meaning that the concentration of oxygen in the atmosphere and oceans would have begun to increase as the quantity of living organisms continued to increase. More oxygen in the water and atmosphere would have helped facilitate the evolution of larger bodied organisms. And to add to this...
11) sequestering CO2 as organic matter would have also helped lower the overall temperature of the early Cambrian Earth. The Cryogenian is weird and also quite debatable as to how it happened and how the Earth came out of it. But other than these phases of glaciation, the Proterozoic and early Phanerpzoic Earth were very warm. And warm water doesn't hold as much oxygen (or any dissolved gas) as cooler water. So a cooler global ocean that is less variable, would be more conducive to life. That is because it isn't just necessary that oxygen concentrations are high enough for respiring life, but the concentration of oxygen can't get too low due to the diurnal cycles. Meaning that it doesn't do respiring organisms any good for oxygen concentrations to be good at night when it is cooler, only for the oceans to get too hot during the day (which would cause the oceans to become dysoxic to anoxic in places). And on top of that...
12) most macroinvertebrates can't withstand temperatures in excess of ~34°C for prolonged periods of time. So the oceans becoming more thermally stable would have also benefited the very organisms that will eventually begin to diversify during the Cambrian Explosion. And then on top of all of this...
13) the temperature of the water as well as the concentration of CO2 in it, will effect the solubility of aragonite and calcite (each are CaCO3). These are the two primary minerals used in the exoskeletons of organisms (even for some arthropods they use calcite to reinforce their exoskeletons. That is why the claws of crabs are so tough. And early Arthropods present in the Cambrian used calcite to reinforce their shells too, like trilobites). This change in solubility would have made it easier to produce shells. And shells are much easier to preserve than soft-bodied organsims because the shells and skeletons don't decompose. So as long as they get buried before being destroyed, they should produce a fossil (which could later be dissolved away by groundwater but that could still leave behind a mold or cast or a recrystallized fossil or a permineralized fossil or a fossil with a new mineralogy having precipitated out in its place in a process called replacement).

So what that ultimately means is that the "Explosion" of hard-bodied organisms was likely a consequence of:
1) increased nutrient input into the oceans
2) change in the global carbon cycle due to an increase in standing biomass
3) sequestration of CO2
4) increase in O2
5) reduction in global mean temperatures and stabilization of temperatures
6) increased concentrations of carbonate ions in the water and increased alkalinity facilitating the development of biomineralization in animals


Two additional important points:
1) Weird Cambrian preservation has produced a diversity observed in the fossil record that is very rare. The Burgess Shale and the Chengjiang faunas are both early Cambrian and both have exceptionally well-preserved soft-bodied animals (the latter has the oldest known chordate, our direct ancestor). These extremely rare instances of preservation happen to be in the early Cambrian and if not for them, we wouldn't know about the bulk of the animals preserved. We wouldn't know about the early Chordates nor the priapulid worms nor any of the primarily soft-bodied animals. Meaning that if we didn't have these two fossil localities, the Cambrian Explosion wouldn't look anywhere near as sudden or odd with respect to the fossil record. Basically, we got lucky for those preservation conditions to have existed and even luckier someone found them.

The Burgess Shale, for instance, is quite intriguing. It is a locality up in the Canadian Rockies and is only accessible for a few months out of the year in the summer. In the mid-1800's, it was discovered by accident when a horse kicked over a slab that had a weird fossil on it. The Burgess Shale is part of a turbidite, which is an underwater mass slump deposit that occurs on the edge of a continental shelf. The organisms preserved were alive on the upper portion of the shelf when it became unstable and collapsed, taking all of them with it. They were deposited in the debris flow along the abyssal plain and essentially buried alive. Those organisms were deposited suddenly in a debris flow into an environment with very little to no oxygen. This prevented them from decomposing and left us with fossils that are so well preserved, you can still dissect them. And on top of that, different imaging techniques reveal new details. For instance, x-raying the trilobites reveals the antennae, legs, and gills. These are all structures that are almost never preserved with trilobites during the nearly 300 million years they were around. So the Cambrian Fauna is in part weird and extremely diverse because of pure dumb luck (lucky for us but not so much for them).

2) it was never an "explosion." This is pretty much the same story as the tale of it being called the Big "Bang." It is a misnomer. The fossils of the early Cambrian appear "suddenly" with respect to geology. What that means is that it occurred over millions of years. So it wasn't so much an "explosion" because that implies that the diversification would have been observable to a human within a matter of seconds, minutes, hours, days. That was never what it meant. Cambrian "Explosion" really just meant that there is a point in the rock record where the quantity and diversity of fossils increases rapidly over a short stratigraphic distance.
Great post, thank you for sharing it.

What do you make of the info on this site that suggests the oxygen and glaciation theories are not that convincing. If they're not, a lot of your post after points 7 and 8 seem to be in doubt. Sorry if that sounds like a personal attack it's not meant to be. I'm just struggling with words here.

http://burgess-shale.rom.on.ca/en/scienc...n.php#box7

Oxygen
However, there does not seem to be much variation in oxygen levels across the Ediacaran-Cambrian boundary. Earlier increases might have triggered the evolution of large Ediacaran metazoans prior to the explosion, and a subsequent post-explosion rise in oxygen levels may have allowed animals to adopt more active, energy-intensive lifestyles such as swimming and hunting.

Glaciation
Unfortunately for the hypothesis, the last worldwide glaciation seems to have ended around 635 million years ago - nearly 90 million years before the first signs of the Cambrian explosion in the fossil record (which was followed by another major regional glaciation around 580 million years ago).

It doesn't really give much info to respond to other than the author doesn't find either of these hypotheses convincing. I think people are looking for a trigger to the Cambrian Explosion that is within a very close timeframe to the appearance of the fossils in the rock record, but that's a pretty narrow view considering that the build-up of oxygen in the atmosphere would have occurred over a prolonged period of time.

And the author makes a fundamental error in saying that it is photosynthesis that would have caused a rise in atmospheric O2. That isn't what drives long-term trends in oxygen concentration in the atmosphere/oceans.

When photosynthesizing organisms first evolved ~3 or so billion years ago, the oxygen that they produced was consumed by iron in the water column (producing Banded Iron Formations). It wasn't until after the reactive iron in the oceans was effectively removed that photosynthesizing organisms would have started to increase atmospheric O2 levels. That gets oxygen into the atmosphere, but not a lot of it. What would have caused an appreciable increase in the amount of O2 in the atmosphere would have been the global carbon cycle and the sequestration of CO2 as organic matter, leaving more O2 in the atmosphere. So an increase in the standing biomass during the late Proterozoic and early Cambrian, plus sequestration of organic matter into the sediments, would have resulted in a rise in atmospheric O2.

Glaciation during the Snowball Earth events wouldn't have been a direct trigger either. Think of it as a perturbation that upset the status quo by introducing large amounts of nutrients to the ocean. This could have helped spur the radiation of the Ediacaran faunas that in turn gave rise to the Cambrian Faunas (most of the Ediacaran biota went extinct and have no direct ancestors. But among them were the ancestors to sponges and probably molluscs. And the soft-bodied vermiform organisms leaving behind the traces, well they would have probably represented a wide range of animal phyla and/or the ancestors to those animal phyla). The other objections the author has to the Snowball Earth idea is that ecosystems would have been severely stressed during the Snowball Earth events. Leading some scientists to call it a "Slushball" Earth instead so as to allow for open water at the low latitudes. None of these issues associated with the Snowball Earth events are directly relevant to the Cambrian Explosion. They are a separate set of questions related to how life survived and adapted to the extreme conditions of a global glaciation.


Don't get me wrong, I am not saying that the Cambrian Explosion is a resolved issue. Much of this is on-going work and a lot of it has shifted to geochemistry to try and determine what is happening with respect to life, climate, and oceans during intervals where fossils are rare or nonexistent. New techniques are being developed to try and better estimate oxygen concentrations for instance. Right now it is very difficult to say what the concentration of oxygen in the atmosphere was for most of the geologic record. Our accuracy gets better forward in time when we have more proxies that are well preserved.


Here is the big take-home point: The Cambrian Explosion isn't real all that much of an enigma any more. We have several hypotheses that can help explain the diversification of hard-bodied organisms and the most likely explanation is that they are all occurring simultaneously. What the big hang-up is in paleontology and geochemistry is: "What trigger initiated the whole thing?" And the answer to that is incredibly difficult to determine because of a number of things:
1) temporal resolution in the rock record is extremely tough and only gets tougher the further back in time we go. The early Cambrian and Proterozoic are not spans of time that are easy to decipher
2) temporal resolution in the rock record is tough even when not in the early Cambrian and Proterozoic. Rocks and sediments don't directly correspond to spans of time. They represent deposition of material over some span of time, but that can also include periods of no deposition and/or erosion. An error many people make is in trying to look directly at the type and thickness of a rock unit to determine how much time it represents. While you can estimate approximately how much time it could have taken to deposit it, that still leaves you with the issue of disconformities (periods of non-deposition and/or erosion) that can make a section of rock represent more time than you might estimate. Constraining the time a sequence of rocks were deposited in (and therefore the ages of the fossils) requires the ability to use radiometric dating. Sometimes we find ash deposits in the sedimentary rocks, which are great for dating but they aren't always conveniently placed or present. Once we know from the radiometric ages how old different species are, we can use them as analogs to tell time with (biostratigraphy), but that doesn't really work for the Proterozoic since there weren't many fossils there to begin with.

What pts 1 and 2 mean is that the interval of rock that is of interest (the rock below the Cambrian Explosion) is hard to place in the context of time. That makes it hard to correlate units around the globe so as to determine if a geochemical signal in one area corresponds to a similar trend in a different area. The good thing about the geochemical record is that it (depending on what element and/or isotopes you are interested in) is a global signal. What that means is that we can also use geochemical trends as tools for correlating rock units and estimating time (chemostratigraphy).

3) Different sediments accumulate at different rates, and the types of sedimentary rocks have also changed through time. You don't really get the same kinds of sedimentary rocks in the Proterozoic and early Cambrian as you do in the rest of the Phanerozoic. But even still, the coarser the grains, the faster the deposition. So 1 m of sand and 1 m of mud don't represent the same amount of time it took for them to be deposited. You can see this yourself if you take a jar and put mud and sand in it along with some water. Shake it up and watch the sand settle out immediately, followed by the slow settling of silts and flocculated mud grains, but most of the mud will have to settle out over the coming hours to days. The reason I bring this up is that it goes along with how we try and match up the rocks to one another globally to get a better idea of the global signal. Telling time in the rocks is not as easy as it might seem.
4) And on top of this, the majority of rocks exposed at the Earth's surface for us to study are Phanerozoic in age. So much of the rock that represents the time interval we want to study with respect to the Cambrian Explosion, simply isn't exposed.

[Image: pO2.png]
There is a lot going on in the above graph, so I will try and explain it a little:
The x-axis is the geologic timescale
Black line: represents the quantity of rock that is of that age and you can see that the amount of rock increases drastically by the Phanerozoic, scale on y-axis on the left (this is because of how rock is recycled due to plate tectonics. The rock used to be there but has been removed, recycled, or buried too deep to be exposed)
Purple line/bar: Compiled data that estimates the trend in atmospheric oxygen content thorough time, scale is in purple on the right.
Blue bar labeled "eukaryotes": When the eukaryotes first appear in the fossil record
Blue shaded area labeled "metazoans": When true animals first appear plus their diversity through time (looks like it is a curve from a guy named Alroy)
Red bar labeled "prokaryotes": When prokaryotes first appear
Green bar labeled "oxygenic photosynthesis": When prokaryotes that undergo oxygenic photosynthesis first appear (not all photosynthesis produces oxygen)

By all accounts, you can't diversify the animals or evolve larger bodied animals without first increasing oxygen concentrations. You simply don't get diverse or large animals in oxygen-deprived habitats. So O2 concentrations had to increase before the Cambrian Explosion. But life may have played a role in that increase in O2 via the aforementioned global carbon cycle (hard to see how it wouldn't have played a role because of how the feedback loops work).

Being nice is something stupid people do to hedge their bets
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05-07-2017, 11:37 AM
RE: The Cambrian Explosion
(05-07-2017 10:56 AM)TheBeardedDude Wrote:  
(05-07-2017 09:50 AM)SeaJay Wrote:  Great post, thank you for sharing it.

What do you make of the info on this site that suggests the oxygen and glaciation theories are not that convincing. If they're not, a lot of your post after points 7 and 8 seem to be in doubt. Sorry if that sounds like a personal attack it's not meant to be. I'm just struggling with words here.

http://burgess-shale.rom.on.ca/en/scienc...n.php#box7

Oxygen
However, there does not seem to be much variation in oxygen levels across the Ediacaran-Cambrian boundary. Earlier increases might have triggered the evolution of large Ediacaran metazoans prior to the explosion, and a subsequent post-explosion rise in oxygen levels may have allowed animals to adopt more active, energy-intensive lifestyles such as swimming and hunting.

Glaciation
Unfortunately for the hypothesis, the last worldwide glaciation seems to have ended around 635 million years ago - nearly 90 million years before the first signs of the Cambrian explosion in the fossil record (which was followed by another major regional glaciation around 580 million years ago).

It doesn't really give much info to respond to other than the author doesn't find either of these hypotheses convincing. I think people are looking for a trigger to the Cambrian Explosion that is within a very close timeframe to the appearance of the fossils in the rock record, but that's a pretty narrow view considering that the build-up of oxygen in the atmosphere would have occurred over a prolonged period of time.

And the author makes a fundamental error in saying that it is photosynthesis that would have caused a rise in atmospheric O2. That isn't what drives long-term trends in oxygen concentration in the atmosphere/oceans.

When photosynthesizing organisms first evolved ~3 or so billion years ago, the oxygen that they produced was consumed by iron in the water column (producing Banded Iron Formations). It wasn't until after the reactive iron in the oceans was effectively removed that photosynthesizing organisms would have started to increase atmospheric O2 levels. That gets oxygen into the atmosphere, but not a lot of it. What would have caused an appreciable increase in the amount of O2 in the atmosphere would have been the global carbon cycle and the sequestration of CO2 as organic matter, leaving more O2 in the atmosphere. So an increase in the standing biomass during the late Proterozoic and early Cambrian, plus sequestration of organic matter into the sediments, would have resulted in a rise in atmospheric O2.

Glaciation during the Snowball Earth events wouldn't have been a direct trigger either. Think of it as a perturbation that upset the status quo by introducing large amounts of nutrients to the ocean. This could have helped spur the radiation of the Ediacaran faunas that in turn gave rise to the Cambrian Faunas (most of the Ediacaran biota went extinct and have no direct ancestors. But among them were the ancestors to sponges and probably molluscs. And the soft-bodied vermiform organisms leaving behind the traces, well they would have probably represented a wide range of animal phyla and/or the ancestors to those animal phyla). The other objections the author has to the Snowball Earth idea is that ecosystems would have been severely stressed during the Snowball Earth events. Leading some scientists to call it a "Slushball" Earth instead so as to allow for open water at the low latitudes. None of these issues associated with the Snowball Earth events are directly relevant to the Cambrian Explosion. They are a separate set of questions related to how life survived and adapted to the extreme conditions of a global glaciation.


Don't get me wrong, I am not saying that the Cambrian Explosion is a resolved issue. Much of this is on-going work and a lot of it has shifted to geochemistry to try and determine what is happening with respect to life, climate, and oceans during intervals where fossils are rare or nonexistent. New techniques are being developed to try and better estimate oxygen concentrations for instance. Right now it is very difficult to say what the concentration of oxygen in the atmosphere was for most of the geologic record. Our accuracy gets better forward in time when we have more proxies that are well preserved.


Here is the big take-home point: The Cambrian Explosion isn't real all that much of an enigma any more. We have several hypotheses that can help explain the diversification of hard-bodied organisms and the most likely explanation is that they are all occurring simultaneously. What the big hang-up is in paleontology and geochemistry is: "What trigger initiated the whole thing?" And the answer to that is incredibly difficult to determine because of a number of things:
1) temporal resolution in the rock record is extremely tough and only gets tougher the further back in time we go. The early Cambrian and Proterozoic are not spans of time that are easy to decipher
2) temporal resolution in the rock record is tough even when not in the early Cambrian and Proterozoic. Rocks and sediments don't directly correspond to spans of time. They represent deposition of material over some span of time, but that can also include periods of no deposition and/or erosion. An error many people make is in trying to look directly at the type and thickness of a rock unit to determine how much time it represents. While you can estimate approximately how much time it could have taken to deposit it, that still leaves you with the issue of disconformities (periods of non-deposition and/or erosion) that can make a section of rock represent more time than you might estimate. Constraining the time a sequence of rocks were deposited in (and therefore the ages of the fossils) requires the ability to use radiometric dating. Sometimes we find ash deposits in the sedimentary rocks, which are great for dating but they aren't always conveniently placed or present. Once we know from the radiometric ages how old different species are, we can use them as analogs to tell time with (biostratigraphy), but that doesn't really work for the Proterozoic since there weren't many fossils there to begin with.

What pts 1 and 2 mean is that the interval of rock that is of interest (the rock below the Cambrian Explosion) is hard to place in the context of time. That makes it hard to correlate units around the globe so as to determine if a geochemical signal in one area corresponds to a similar trend in a different area. The good thing about the geochemical record is that it (depending on what element and/or isotopes you are interested in) is a global signal. What that means is that we can also use geochemical trends as tools for correlating rock units and estimating time (chemostratigraphy).

3) Different sediments accumulate at different rates, and the types of sedimentary rocks have also changed through time. You don't really get the same kinds of sedimentary rocks in the Proterozoic and early Cambrian as you do in the rest of the Phanerozoic. But even still, the coarser the grains, the faster the deposition. So 1 m of sand and 1 m of mud don't represent the same amount of time it took for them to be deposited. You can see this yourself if you take a jar and put mud and sand in it along with some water. Shake it up and watch the sand settle out immediately, followed by the slow settling of silts and flocculated mud grains, but most of the mud will have to settle out over the coming hours to days. The reason I bring this up is that it goes along with how we try and match up the rocks to one another globally to get a better idea of the global signal. Telling time in the rocks is not as easy as it might seem.
4) And on top of this, the majority of rocks exposed at the Earth's surface for us to study are Phanerozoic in age. So much of the rock that represents the time interval we want to study with respect to the Cambrian Explosion, simply isn't exposed.

[Image: pO2.png]
There is a lot going on in the above graph, so I will try and explain it a little:
The x-axis is the geologic timescale
Black line: represents the quantity of rock that is of that age and you can see that the amount of rock increases drastically by the Phanerozoic, scale on y-axis on the left (this is because of how rock is recycled due to plate tectonics. The rock used to be there but has been removed, recycled, or buried too deep to be exposed)
Purple line/bar: Compiled data that estimates the trend in atmospheric oxygen content thorough time, scale is in purple on the right.
Blue bar labeled "eukaryotes": When the eukaryotes first appear in the fossil record
Blue shaded area labeled "metazoans": When true animals first appear plus their diversity through time (looks like it is a curve from a guy named Alroy)
Red bar labeled "prokaryotes": When prokaryotes first appear
Green bar labeled "oxygenic photosynthesis": When prokaryotes that undergo oxygenic photosynthesis first appear (not all photosynthesis produces oxygen)

By all accounts, you can't diversify the animals or evolve larger bodied animals without first increasing oxygen concentrations. You simply don't get diverse or large animals in oxygen-deprived habitats. So O2 concentrations had to increase before the Cambrian Explosion. But life may have played a role in that increase in O2 via the aforementioned global carbon cycle (hard to see how it wouldn't have played a role because of how the feedback loops work).
You have obviously studied this and know quite a lot about it. I'm not going to even try to gainsay the above because I don't have the academic knowledge to do so. It sounds very plausible though. I can also appreciate just how difficult it is to pin point anything specific concerning the Cambrian Explosion era, but I think I know enough now, from the posts here and my initial research to say that the CE isn't as anxiety provoking as I first thought it was. There's still a ton I don't understand and I may just be nodding along to what is being said here, but the impression I get is that there's no real problem with the CE in as far as evolution is concerned. It's a subject I should find fascinating not frightening.

Thank you very much for your detailed responses and thanks to all who contributed. Very much appreciated.

“I am so clever that sometimes I don't understand a single word of what I am saying.” ~ Oscar Wilde
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05-07-2017, 11:43 AM
RE: The Cambrian Explosion
(05-07-2017 11:37 AM)SeaJay Wrote:  
(05-07-2017 10:56 AM)TheBeardedDude Wrote:  It doesn't really give much info to respond to other than the author doesn't find either of these hypotheses convincing. I think people are looking for a trigger to the Cambrian Explosion that is within a very close timeframe to the appearance of the fossils in the rock record, but that's a pretty narrow view considering that the build-up of oxygen in the atmosphere would have occurred over a prolonged period of time.

And the author makes a fundamental error in saying that it is photosynthesis that would have caused a rise in atmospheric O2. That isn't what drives long-term trends in oxygen concentration in the atmosphere/oceans.

When photosynthesizing organisms first evolved ~3 or so billion years ago, the oxygen that they produced was consumed by iron in the water column (producing Banded Iron Formations). It wasn't until after the reactive iron in the oceans was effectively removed that photosynthesizing organisms would have started to increase atmospheric O2 levels. That gets oxygen into the atmosphere, but not a lot of it. What would have caused an appreciable increase in the amount of O2 in the atmosphere would have been the global carbon cycle and the sequestration of CO2 as organic matter, leaving more O2 in the atmosphere. So an increase in the standing biomass during the late Proterozoic and early Cambrian, plus sequestration of organic matter into the sediments, would have resulted in a rise in atmospheric O2.

Glaciation during the Snowball Earth events wouldn't have been a direct trigger either. Think of it as a perturbation that upset the status quo by introducing large amounts of nutrients to the ocean. This could have helped spur the radiation of the Ediacaran faunas that in turn gave rise to the Cambrian Faunas (most of the Ediacaran biota went extinct and have no direct ancestors. But among them were the ancestors to sponges and probably molluscs. And the soft-bodied vermiform organisms leaving behind the traces, well they would have probably represented a wide range of animal phyla and/or the ancestors to those animal phyla). The other objections the author has to the Snowball Earth idea is that ecosystems would have been severely stressed during the Snowball Earth events. Leading some scientists to call it a "Slushball" Earth instead so as to allow for open water at the low latitudes. None of these issues associated with the Snowball Earth events are directly relevant to the Cambrian Explosion. They are a separate set of questions related to how life survived and adapted to the extreme conditions of a global glaciation.


Don't get me wrong, I am not saying that the Cambrian Explosion is a resolved issue. Much of this is on-going work and a lot of it has shifted to geochemistry to try and determine what is happening with respect to life, climate, and oceans during intervals where fossils are rare or nonexistent. New techniques are being developed to try and better estimate oxygen concentrations for instance. Right now it is very difficult to say what the concentration of oxygen in the atmosphere was for most of the geologic record. Our accuracy gets better forward in time when we have more proxies that are well preserved.


Here is the big take-home point: The Cambrian Explosion isn't real all that much of an enigma any more. We have several hypotheses that can help explain the diversification of hard-bodied organisms and the most likely explanation is that they are all occurring simultaneously. What the big hang-up is in paleontology and geochemistry is: "What trigger initiated the whole thing?" And the answer to that is incredibly difficult to determine because of a number of things:
1) temporal resolution in the rock record is extremely tough and only gets tougher the further back in time we go. The early Cambrian and Proterozoic are not spans of time that are easy to decipher
2) temporal resolution in the rock record is tough even when not in the early Cambrian and Proterozoic. Rocks and sediments don't directly correspond to spans of time. They represent deposition of material over some span of time, but that can also include periods of no deposition and/or erosion. An error many people make is in trying to look directly at the type and thickness of a rock unit to determine how much time it represents. While you can estimate approximately how much time it could have taken to deposit it, that still leaves you with the issue of disconformities (periods of non-deposition and/or erosion) that can make a section of rock represent more time than you might estimate. Constraining the time a sequence of rocks were deposited in (and therefore the ages of the fossils) requires the ability to use radiometric dating. Sometimes we find ash deposits in the sedimentary rocks, which are great for dating but they aren't always conveniently placed or present. Once we know from the radiometric ages how old different species are, we can use them as analogs to tell time with (biostratigraphy), but that doesn't really work for the Proterozoic since there weren't many fossils there to begin with.

What pts 1 and 2 mean is that the interval of rock that is of interest (the rock below the Cambrian Explosion) is hard to place in the context of time. That makes it hard to correlate units around the globe so as to determine if a geochemical signal in one area corresponds to a similar trend in a different area. The good thing about the geochemical record is that it (depending on what element and/or isotopes you are interested in) is a global signal. What that means is that we can also use geochemical trends as tools for correlating rock units and estimating time (chemostratigraphy).

3) Different sediments accumulate at different rates, and the types of sedimentary rocks have also changed through time. You don't really get the same kinds of sedimentary rocks in the Proterozoic and early Cambrian as you do in the rest of the Phanerozoic. But even still, the coarser the grains, the faster the deposition. So 1 m of sand and 1 m of mud don't represent the same amount of time it took for them to be deposited. You can see this yourself if you take a jar and put mud and sand in it along with some water. Shake it up and watch the sand settle out immediately, followed by the slow settling of silts and flocculated mud grains, but most of the mud will have to settle out over the coming hours to days. The reason I bring this up is that it goes along with how we try and match up the rocks to one another globally to get a better idea of the global signal. Telling time in the rocks is not as easy as it might seem.
4) And on top of this, the majority of rocks exposed at the Earth's surface for us to study are Phanerozoic in age. So much of the rock that represents the time interval we want to study with respect to the Cambrian Explosion, simply isn't exposed.

[Image: pO2.png]
There is a lot going on in the above graph, so I will try and explain it a little:
The x-axis is the geologic timescale
Black line: represents the quantity of rock that is of that age and you can see that the amount of rock increases drastically by the Phanerozoic, scale on y-axis on the left (this is because of how rock is recycled due to plate tectonics. The rock used to be there but has been removed, recycled, or buried too deep to be exposed)
Purple line/bar: Compiled data that estimates the trend in atmospheric oxygen content thorough time, scale is in purple on the right.
Blue bar labeled "eukaryotes": When the eukaryotes first appear in the fossil record
Blue shaded area labeled "metazoans": When true animals first appear plus their diversity through time (looks like it is a curve from a guy named Alroy)
Red bar labeled "prokaryotes": When prokaryotes first appear
Green bar labeled "oxygenic photosynthesis": When prokaryotes that undergo oxygenic photosynthesis first appear (not all photosynthesis produces oxygen)

By all accounts, you can't diversify the animals or evolve larger bodied animals without first increasing oxygen concentrations. You simply don't get diverse or large animals in oxygen-deprived habitats. So O2 concentrations had to increase before the Cambrian Explosion. But life may have played a role in that increase in O2 via the aforementioned global carbon cycle (hard to see how it wouldn't have played a role because of how the feedback loops work).
You have obviously studied this and know quite a lot about it. I'm not going to even try to gainsay the above because I don't have the academic knowledge to do so. It sounds very plausible though. I can also appreciate just how difficult it is to pin point anything specific concerning the Cambrian Explosion era, but I think I know enough now, from the posts here and my initial research to say that the CE isn't as anxiety provoking as I first thought it was. There's still a ton I don't understand and I may just be nodding along to what is being said here, but the impression I get is that there's no real problem with the CE in as far as evolution is concerned. It's a subject I should find fascinating not frightening.

Thank you very much for your detailed responses and thanks to all who contributed. Very much appreciated.

"You have obviously studied this and know quite a lot about it."

I'm a paleontologist, so I better know

"Thank you very much for your detailed responses and thanks to all who contributed. Very much appreciated."

You're welcome

Being nice is something stupid people do to hedge their bets
-Rick
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