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Selfsim
2014-Feb-18, 04:00 AM
Theory on origin of animals challenged: Earliest animal life may have required little oxygen (http://phys.org/news/2014-02-theory-animals-earliest-animal-life.html)
One of science's strongest dogmas is that complex life on Earth could only evolve when oxygen levels in the atmosphere rose to close to modern levels. But now studies of a small sea sponge fished out of a Danish fjord shows that complex life does not need high levels of oxygen in order to live and grow.
...
How could the first small primitive cells evolve into the diversity of advanced life forms that exists on Earth today? The explanation in all textbooks is: Oxygen. Complex life evolved because the atmospheric levels of oxygen began to rise app. 630 – 635 million years ago.
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"Our studies suggest that the origin of animals was not prevented by low oxygen levels", says Daniel Mills, PhD at the Nordic Center for Earth Evolution at the University of Southern Denmark.
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"When we placed the sponges in our lab, they continued to breathe and grow even when the oxygen levels reached 0.5 per cent of present day atmospheric levels", says Daniel Mills.
This is lower than the oxygen levels we thought were necessary for animal life.

The big question now is: If low oxygen levels did not prevent animals from evolving – then what did? Why did life consist of only primitive single-celled bacteria and amoebae for billions of years before everything suddenly exploded and complex life arose?

"There must have been other ecological and evolutionary mechanisms at play".So, just how significant is the presence of free atmospheric oxygen as a 'biomarker', then?

Paul Wally
2014-Feb-18, 09:09 AM
Theory on origin of animals challenged: Earliest animal life may have required little oxygen (http://phys.org/news/2014-02-theory-animals-earliest-animal-life.html)So, just how significant is the presence of free atmospheric oxygen as a 'biomarker', then?

I don't see how this finding makes oxygen less of a biomarker. It only means that there can be false negatives, but we already know that. If you want to build a case against oxygen as a biomarker you will have to find an article about how a free oxygen atmosphere can be produced abiotically on a terrestrial planet/moon. Perhaps oxygen produced on Europa is such an example.

Noclevername
2014-Feb-18, 09:11 AM
IMO you have it backwards. Large ratios of oxygen are used as a biomarker because under known conditions (IE on Earth) they are produced by LAWKI, not because it is used by LAWKI. Photosynthetic plants are life, albeit life that only existed since geologically recently.

Now there are other known methods for breaking H2O molecules, as Europa demonstrates. So it is not and never will be a 100% reliable biomarker. But the conditions there are also measureable from a distance. We know Europa is a radiation-bathed, airless ice moon. To have a planet with a combination of liquid water, atmosphere, and much free oxygen is a situation only known to occur under one condition. That, of course, does not mean we should stop searching for alternative reasons for such a condition. But if we do discover an exoworld that meets these criteria, it would be a sign marking the planet as worthy of closer study than its many, many peers. It would stand out from the crowd as unusual. Again, it's about prioritizing the allocation of limited observational resources, like telescope time and computing power.

Swift
2014-Feb-18, 02:55 PM
Personally, I am less interested in the biomarker question (though it is a good question) and more interested in this:

The big question now is: If low oxygen levels did not prevent animals from evolving – then what did? Why did life consist of only primitive single-celled bacteria and amoebae for billions of years before everything suddenly exploded and complex life arose?
My understand was always that the significant trigger for the development of multicellular life was that the rise of oxygen levels allowed the high energy production of aerobic chemistry, which was necessary for this type of life to flourish.

Does this finding mean that is just wrong? Does it mean that it is still fundamentally correct, but that the concentration of oxygen necessary is a lot lower than was thought (and thus maybe multicellular life evolved earlier than thought)? Is this sponge just weird and is the exception that doesn't prove the rule (for example, high oxygen is still necessary for the evolution of complex life, and this sponge is evolved from such a creature, to survive in a low oxygen environoment)?

I don't even pretend to have the answer, but it is is a fascinating question.

Colin Robinson
2014-Feb-18, 09:45 PM
Personally, I am less interested in the biomarker question (though it is a good question) and more interested in this:

My understand was always that the significant trigger for the development of multicellular life was that the rise of oxygen levels allowed the high energy production of aerobic chemistry, which was necessary for this type of life to flourish.

Does this finding mean that is just wrong? Does it mean that it is still fundamentally correct, but that the concentration of oxygen necessary is a lot lower than was thought (and thus maybe multicellular life evolved earlier than thought)? Is this sponge just weird and is the exception that doesn't prove the rule (for example, high oxygen is still necessary for the evolution of complex life, and this sponge is evolved from such a creature, to survive in a low oxygen environoment)?

I don't even pretend to have the answer, but it is is a fascinating question.

Sponges are less mobile than most multicelled animals, and less internally differentiated — they don't have nerves or muscles, hence they don't have internal organs based on nerves and muscles: no heart, stomach, intestines, brain... All of which means they require less energy than other animals. So it is not altogether surprising that they can tolerate a lower level of free oxygen than others. It would be interesting to compare their oxygen requirements with those of multicelled marine vegetation or fungi.

It may mean that multicelled animal life evolved earlier than thought. But higher concentrations of oxygen may still have been necessary for more mobile animals such as jellyfish.

Selfsim
2014-Feb-18, 11:38 PM
Well the point is that if the relationship between oxygenation and complexification of life is more explanation based, than universal fact, then it may well be that our oxygen breathing habits might, yet again, be mere adaptations, (specific to the case of Earth animals) .. why not, if relatively complex reproducing and metabolising sponges, were already complex before the GOE(?)

This research also demonstrates the potential for false negatives where potentially (spectroscopic) detectable atmospheric oxygen might be absent in a spectrum, resulting in the inferred conclusion of the absence of complex photosynthetically based life.

At present, the explanation for relatively substantial, sustained atmospheric oxygen, (ie: life), is only empirically supported in Earth's known-life instance. In principle, it is also known that any mechanism which suspends say, water vapour, in the upper troposphere or stratosphere equivalents of an exoplanet, can principle, undergo radiation induced photo-dissociation capable of releasing free oxygen, which if retained, could then be easily and falsely inferred as having being caused by photosynthetically based life … ie: a false positive. (The proportions of it detected, would also have to be subject to the resolution precision of the measurement techniques, and the inherent dynamics of the target atmosphere). Currently, the only known basis for discriminating between real and false positives in this scenario, is entirely dependent on the agreed definition of what is, and isn't a 'Habitable Zone' which, from the other thread (http://cosmoquest.org/forum/showthread.php?149135-Superhabitable-Worlds), is seemingly also open to interpretation.

One can easily adopt a stance of skepticism about any inferences related to exo-life, upon objective scrutiny of the potential of false negatives and false positives when based on remote detections. If one chooses to keep track of these accumulating uncertainties, one also finds the predictability of the theoretical end result, also becomes legitimately questionable.

It seems this study has contributed incrementally to empirical knowledge, in this regard.

Noclevername
2014-Feb-19, 01:00 AM
One can easily adopt a stance of skepticism about any inferences related to exo-life, upon objective scrutiny of the potential of false negatives and false positives when based on remote detections. If one chooses to keep track of these accumulating uncertainties, one also finds the predictability of the theoretical end result, also becomes legitimately questionable.


It always has been legitimately questionable. No one here said otherwise, and AFAIK the stance of mainstream astrobiology has always been that any conclusion of life from remote observation was questionable.

Colin Robinson
2014-Feb-19, 01:27 AM
Well the point is that if the relationship between oxygenation and complexification of life is more explanation based, than universal fact, then it may well be that our oxygen breathing habits might, yet again, be mere adaptations, (specific to the case of Earth animals)

Is oxygen respiration specific to Earth animals? No, because it is also done by Earth plants. Also by fungi, algae, aerobic bacteria, aerobic archaea.


.. why not, if relatively complex reproducing and metabolising sponges, were already complex before the GOE(?)

Some points to consider are:

* What specific role do our oxygen-breathing habits play in the way we earth animals function?
* Why would different oxygen-respiring organisms require different levels of oxygen?
* Is it possible that something other than free oxygen could play a similar role on other worlds?

Selfsim
2014-Feb-19, 06:47 AM
Is oxygen respiration specific to Earth animals? No, because it is also done by Earth plants. Also by fungi, algae, aerobic bacteria, aerobic archaea.Yep. Does that make a difference when it comes to the adaptation point?


Some points to consider are:

* What specific role do our oxygen-breathing habits play in the way we earth animals function?
* Why would different oxygen-respiring organisms require different levels of oxygen? Well that's tightly coupled with Kleiber's Law (http://en.wikipedia.org/wiki/Kleiber%27s_Law) (especially as it pertains to cellular respiration):
Kleiber's law, named after Max Kleiber's biological work in the early 1930s, is the observation that, for the vast majority of animals, an animal's metabolic rate scales to the ¾ power of the animal's mass. Symbolically: if q0 is the animal's metabolic rate, and M the animal's mass, then Kleiber's law states that q0 ~ M¾. Thus a cat, having a mass 100 times that of a mouse, will have a metabolism roughly 31 times greater than that of a mouse. In plants, the exponent is close to 1.The latest explanation (http://phys.org/news/2014-02-evolution-geometries-life-scientists-longstanding.html) for this empirical law is:
Picture two organisms: a tree and a tiger. In evolutionary terms, the tree has the easier task: convert sunlight to energy and move it within a body that more or less stays put. To make that task as efficient as possible, the tree has evolved a branching shape with many surfaces – its leaves.

"The tree's surface area and the volume of space it occupies are nearly the same," said physicist Jayanth Banavar, dean of the UMD College of Computer, Mathematical, and Natural Sciences. "The tree's nutrients flow at a constant speed, regardless of its size."
...
"Animals need to adjust the flow of nutrients and heat as their mass changes to maintain the greatest possible energy efficiency. That is why animals need a pump – a heart – and trees do not."
...
"You have these two lineages, plants and animals, that are very different and they arrive at the same conclusion. That is what's called convergent evolution, and the stunning result is that it's being driven by the underlying physics and the underlying math."(Well I don't know about his terminology of 'being driven by the underlying physics and math' .. but that's probably just a language issue ..)
The point is that, (following this explanation), it appears that as organisms acquired more mass (complexity), whatever existing metabolism they had, adjusted itself to maximise energy efficiency, (more or less in accordance with Kleiber's Law) .. all of which doesn't necessarily have to have been directly caused by increases in atmospheric oxygen levels .. they just adapted to the changing levels(?)


* Is it possible that something other than free oxygen could play a similar role on other worlds?Unknown.

Colin Robinson
2014-Feb-19, 10:02 PM
Yep. Does that make a difference when it comes to the adaptation point?

Since O2 level started to rise, many different classes of organisms (lichens, humans, halo-archaea) have come to use the same basic reaction (aerobic respiration) to get energy. Doesn't this suggest that aerobic respiration has serious advantages when compared to other energy sources?


Well that's tightly coupled with Kleiber's Law (http://en.wikipedia.org/wiki/Kleiber%27s_Law) (especially as it pertains to cellular respiration):


Kleiber's law, named after Max Kleiber's biological work in the early 1930s, is the observation that, for the vast majority of animals, an animal's metabolic rate scales to the ¾ power of the animal's mass. Symbolically: if q0 is the animal's metabolic rate, and M the animal's mass, then Kleiber's law states that q0 ~ M¾. Thus a cat, having a mass 100 times that of a mouse, will have a metabolism roughly 31 times greater than that of a mouse. In plants, the exponent is close to 1.

It is all very well to compare the metabolic rates of a cat and a mouse, which are both quadruped mammals, but surely another thing to compare the metabolism of a sessile animal like a sponge with the metabolism of a motile organism?


The point is that, (following this explanation), it appears that as organisms acquired more mass (complexity),

Not sure whether mass and complexity can be equated: is a large heavy jellyfish more complex than a small crustacean such as a shrimp?


whatever existing metabolism they had, adjusted itself to maximise energy efficiency, (more or less in accordance with Kleiber's Law) .. all of which doesn't necessarily have to have been directly caused by increases in atmospheric oxygen levels .. they just adapted to the changing levels(?)

There is no doubt that organisms have evolved for energy efficiency. The point is, rising levels of free oxygen offered organisms an energy resource they previously didn't have.

Perhaps it was comparable to getting the electricity connected for the first time?

Selfsim
2014-Feb-20, 05:40 AM
Y'know .. as I look over Wiki's text about the GOE (http://en.wikipedia.org/wiki/Great_Oxygenation_Event), I'm quite overwhelmed by the assurity implied by the language used. For example:

The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe or Oxygen Crisis or Great Oxidation, was the biologically induced appearance of free oxygen (O2) in Earth's atmosphere. Geological, isotopic, and chemical evidence suggest this major environmental change happened around 2.4 billion years ago (2.4 Ga).

Cyanobacteria, which appeared about 200 million years before the GOE, began producing oxygen by photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron or organic matter. The GOE was the point when these oxygen sinks became saturated and could not capture all of the oxygen that was produced by cyanobacterial photosynthesis. After the GOE the excess free oxygen started to accumulate in the atmosphere.(Note my underlined and emboldened bits ... very assertive language stated as fact!)

Ok, so as I read it, I'm thinking: "Ok .. I'll believe it ... for a minute .. or at least until I get to the evidence bit" .. but alas, sadly there is no evidence presented which supports the complexification of life with past measurements of O2 atmospheric buildup! Its all just speculation based on a correlated bunch of measurements, and their hypothesised and highly generalised implications! Its not really worth more than the test done by Mills (in the OP), and the electrons its written with! Granted, it may just be the way the Wiki text is written .. but 'where there's smoke, there's usually fire' (well maybe).

If the Wiki article is the best which can be done to defend such a speculative idea, particularly when confronted with the empirical test it generated (see the OP) ... which then appears to contradict it ... well, all can I say is that I'm now quite happy to put the mighty 'GOE' into the context it so rightly deserves ... ie: a purely speculative story .. akin to the much beloved sc-fi ones!

John Mendenhall
2014-Feb-20, 07:25 AM
Y'know .. as I look over Wiki's text about the GOE (http://en.wikipedia.org/wiki/Great_Oxygenation_Event), I'm quite overwhelmed by the assurity implied by the language used. For example:
(Note my underlined and emboldened bits ... very assertive language stated as fact!)

Ok, so as I read it, I'm thinking: "Ok .. I'll believe it ... for a minute .. or at least until I get to the evidence bit" .. but alas, sadly there is no evidence presented which supports the complexification of life with past measurements of O2 atmospheric buildup! Its all just speculation based on a correlated bunch of measurements, and their hypothesised and highly generalised implications! Its not really worth more than the test done by Mills (in the OP), and the electrons its written with! Granted, it may just be the way the Wiki text is written .. but 'where there's smoke, there's usually fire' (well maybe).

If the Wiki article is the best which can be done to defend such a speculative idea, particularly when confronted with the empirical test it generated (see the OP) ... which then appears to contradict it ... well, all can I say is that I'm now quite happy to put the mighty 'GOE' into the context it so rightly deserves ... ie: a purely speculative story .. akin to the much beloved sc-fi ones!

Selfsim, you have touched a nerve. I have been uncomfortable for years with the oxygen event. Any others? I would love to hear of some evidence other than correlation.

Selfsim
2014-Feb-20, 09:38 AM
This is great ... I finally found their paper .. Mills etal is here (http://www.pnas.org/content/early/2014/02/13/1400547111.full.pdf+html).

They even have a parting shot directed at addressing 'the Origin' question ...

Therefore, it is possible that the oxygen content of the atmosphere was completely permissive to the origin and early evolution of sponge-grade metazoans well before their evolutionary first appearance. This would mean, in turn, that the origin of animal life did not require a concurrent oxygenation event. Indeed, biological developments, such as the evolution of sophisticated gene regulatory networks, may have controlled the timing of animal origins more so than environmental parameters. Overall, animal-grade multicellularity likely required the accumulation and integration of specific traits, including cell adhesion molecules necessary for multicellular body plans, signaling proteins for cell–cell communication, and transcription factors essential for coordinated development. The accumulation of these traits and not the enhanced availability of oxygen may have controlled the onset of animal evolution.Well, I can see that if these sponges were reproducing at these low oxygen levels, then evolution and natural selection would have also been in operation. (The study doesn't mention anything about reproduction of the lab sponges during the trial, however).

Selfsim
2014-Feb-20, 09:43 AM
Selfsim, you have touched a nerve. I have been uncomfortable for years with the oxygen event. Any others? I would love to hear of some evidence other than correlation.Hmm .. me too .. There must be something more concrete than a story which is consistent with a bunch of other stories .. surely .. no(?)

Noclevername
2014-Feb-20, 09:44 AM
Therefore, it is possible

Sounds like speculation to me. :evil:

Selfsim
2014-Feb-20, 09:48 AM
Sounds like speculation to me. :evil:Sure is .. speculation to counter speculation .. except these guys have actually struck a blow and done the experiment! Which is kind of refreshing, eh? They are actually armed with empirical evidence .. Is there any to be found from the GOE camp, tho?

Noclevername
2014-Feb-20, 09:55 AM
Sure is .. speculation to counter speculation .. except these guys have actually struck a blow and done the experiment! Which is kind of refreshing, eh? They are actually armed with empirical evidence .. Is there any to be found from the GOE camp, tho?

"Camp?" Is this science or a debate club?

The purported connection between the GOE and the rise of animal life has always been subject to revision as new data becomes available, like all hypotheses and theories. For a while, based on the knowledge we had available, it looked like there was a connection; now we find there may not be. We now have a little more data to consider, that's all.

Selfsim
2014-Feb-20, 10:12 AM
"Camp?" Is this science or a debate club? You're right! :)
If the Wiki page is purely a consensus result, then it must have come from a debate club!

The purported connection between the GOE and the rise of animal life has always been subject to revision as new data becomes available, like all hypotheses and theories. For a while, based on the knowledge we had available, it looked like there was a connection; now we find there may not be. We now have a little more data to consider, that's all.I'm sorry Noclever ... that Wiki page makes no references to hypotheses other than by way of speculating about:
the gap between the start of oxygen production from photosynthetic organisms and the geologically rapid increase in atmospheric oxygen (about 2.5–2.4 billion years ago) may have been as long as 900 million years. Several hypotheses might explain the time lag"The actual causal connection between the apparent rise in atmospheric oxygen and complexification of species however, is worded as though its all fact.
That Wiki page is a shocker! :)

Noclevername
2014-Feb-20, 10:16 AM
Your right! :)
If the Wiki page is purely a consensus result, then it must have come from a debate club!
I'm sorry Noclever ... that Wiki page makes no references to hypotheses other than by way of speculating about:The actual causal connection between the apparent rise in atmospheric oxygen and complexification of species however, is worded as though its all fact.
That Wiki page is a shocker! :)

At no time did I mention Wikipedia. I quoted from the paper you linked (http://www.pnas.org/content/early/2014/02/13/1400547111.full.pdf+html), and then talked about science.

Selfsim
2014-Feb-20, 10:25 AM
At no time did I mention Wikipedia. I quoted from the paper you linked (http://www.pnas.org/content/early/2014/02/13/1400547111.full.pdf+html), and then talked about science.Right again! :)

Noclevername
2014-Feb-20, 10:28 AM
Right again! :)

So what Wikipedia page were you talking about?

EDIT: I assume it's the one you referenced earlier. What Wikipedia has to do with what I was saying is uncertain. What's the connection?

Colin Robinson
2014-Feb-20, 06:32 PM
You're right! :)
If the Wiki page is purely a consensus result, then it must have come from a debate club!
I'm sorry Noclever ... that Wiki page makes no references to hypotheses other than by way of speculating about:The actual causal connection between the apparent rise in atmospheric oxygen and complexification of species however, is worded as though its all fact.
That Wiki page is a shocker! :)

The Wiki page you're shocked about actually says nothing at all about the specific question of how multicelled animal life got started.

It contains a sentence about the appearance of the first mitochondria, which is a different question, relating to an earlier stage in evolutionary history.

Colin Robinson
2014-Feb-20, 08:58 PM
Yes, it is interesting to know that sponges can metabolize and grow with such a low level of free oxygen. But at least one other species of multicelled animal, a variety of loricifera, has been identified as living and reproducing in an environment with no free oxygen at all.

See the thread from April 2010 Complex Anaerobic Life Found! (http://cosmoquest.org/forum/showthread.php?102858-Complex-Anaerobic-Life-Found!)

Loricifera don't grow as large as sponges, but they are structurally more sophisticated — they have symmetry, and a digestive tract, both of which sponges lack.

Selfsim
2014-Feb-20, 09:58 PM
The Wiki page you're shocked about actually says nothing at all about the specific question of how multicelled animal life got started.

It contains a sentence about the appearance of the first mitochondria, which is a different question, relating to an earlier stage in evolutionary history.I think you may be having some misgivings about accepting the implications of this study, maybe because no specific definition of 'complexity' is provided(?) I've noticed, (from past discussions), definitions seem to be all important for full-time speculators, whereas concepts can still hold, regardless of the particular specifications constrained by the verbiage of a particular definition.

So as an understanding aid, here's my attempt at providing a crude definition in this case.

The sponges examined in the study are considered 'complex' because they:

i) are multicellular;
ii) have multiple cell types that differentiate from progenitor stem-like cells which then go on to form multi-functional colonies (with cells specialising in digestion, reproduction, etc)
iii) they have simple tissues;
iv) they do extra- and intra-cellular digestion (mostly filter feeders);
v) they do sexual/asexual reproduction.

And it appears that if these sponges are accepted as an analogue for the physiology and oxygen requirements of the last common ancestor of all living animals, then the atmospheric oxygen environment prior to the GOE, was not sufficiently low enough for ruling out the existence of the above functional complexities. This statement is based on empirical evidence and a present-day model which is also supportable from the evidence of its own particular evolutionary phylogenetic pathway.

If you disagree with this, then you should cite your evidence basis for that disagreement.

Noclevername
2014-Feb-20, 10:08 PM
Selfsim, I'll ask again: Why did you, addressing my post #17, instead bring up the unrelated subject of Wikipedia? I was making specific points, which you seemed to ignore.

As for definitions, since they are a necessary part of clear communication, I would not say their importance is limited to those you label "full-time speculators".

Selfsim
2014-Feb-20, 10:12 PM
Yes, it is interesting to know that sponges can metabolize and grow with such a low level of free oxygen. But at least one other species of multicelled animal, a variety of loricifera, has been identified as living and reproducing in an environment with no free oxygen at all.

See the thread from April 2010 Complex Anaerobic Life Found! (http://cosmoquest.org/forum/showthread.php?102858-Complex-Anaerobic-Life-Found!)

Loricifera don't grow as large as sponges, but they are structurally more sophisticated — they have symmetry, and a digestive tract, both of which sponges lack.The point of the OP study was to examine metabolic response to low oxygen environments because this appears to have never been previously investigated.

H.panicea is sensitive to oxygen, and can both tolerate and grow at low oxygen levels from 0.5% to 4% PAL, {Present Atmospheric Levels}, which happens to correspond with the atmospheric levels present in the environment "before animals originated", thus, "animal evolution may not have been prohibited by the presumably low atmospheric oxygen levels before the Neoproterozoic Era".

Colin Robinson
2014-Feb-21, 12:43 AM
As for definitions, since they are a necessary part of clear communication, I would not say their importance is limited to those you label "full-time speculators".

Well said. :)

Colin Robinson
2014-Feb-21, 12:54 AM
I think you may be having some misgivings about accepting the implications of this study, maybe because no specific definition of 'complexity' is provided(?)

I think the implications of the study have been hyped up; not in the paper itself, but in the popularization of it at Phys Org which you linked to in the OP, and also in this thread. I do have misgivings about the way the term "complex" is being used.

The paper itself does not use the term "complex life" as far as I can see, instead it talks about "the earliest metazoans", metazoan being a term with a well-established meaning.

Appearance of the first (probably sessile) metazoans was undoubtedly an important moment in evolution, but describing them as "the first forms of complex life" (words used in the Phys Org story) is simplistic journalese.

No doubt sponges are "complex" in comparison to single-celled eukaryotes, but isn't it just as true to say that single-celled eukaryotes are "complex" in comparison with bacteria and archaea?

I also think it is important to keep in mind the distinction between multicellular animals (metazoans) and the broader category of multicellular organisms. All metazoans are multicellular, but not all multicellular organisms are metazoans.

Selfsim
2014-Feb-21, 05:56 AM
Selfsim, I'll ask again: Why did you, addressing my post #17, instead bring up the unrelated subject of Wikipedia? I was making specific points, which you seemed to ignore.From the Mills paper:
A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth.From the PhysOrg article:
How could the first small primitive cells evolve into the diversity of advanced life forms that exists on Earth today? The explanation in all textbooks is: Oxygen. Complex life evolved because the atmospheric levels of oxygen began to rise app. 630 – 635 million years ago.From the Wiki text on the GOE:
... Despite the natural recycling of organic matter, life had remained energetically limited until the widespread availability of oxygen. This breakthrough in metabolic evolution greatly increased the free energy supply to living organisms, having a truly global environmental impact; mitochondria evolved after the GOE.All three of the above sources confirm the popularity of the idea that animal life (including its mitochondria) followed the GOE, as a consequence of the GOE. What isn't ruled out, is that both animals and their mitochondria-based aerobic respiration capabilities, could also have existed prior to the GOE, (as is now revealed by the test). The Wiki article completely overlooks this as a possibility, which is highly misleading. An error of omission in this case, results in a major misperception. This is why I referenced the Wiki GOE text as appearing to be the result of some type of speculative debate (rather than being an empirically accurate portrayal of only the constraints provided by the evidence in hand).

The rest of what you have had to say so far in this thread, seems to be concerned with questioning my reasons for starting the thread. I find such a discussion particularly uninspiring and OT, and as a consequence, I have nothing to say about this.

Colin Robinson
2014-Feb-21, 06:50 AM
From the Mills paper:From the PhysOrg article:From the Wiki text on the GOE:All three of the above sources confirm the popularity of the idea that animal life (including its mitochondria) followed the GOE, as a consequence of the GOE. What isn't ruled out, is that both animals and their mitochondria-based aerobic respiration capabilities, could also have existed prior to the GOE, (as is now revealed by the test). The Wiki article completely overlooks this as a possibility, which is highly misleading. An error of omission in this case, results in a major misperception. This is why I referenced the Wiki GOE text as appearing to be the result of some type of speculative debate (rather than being an empirically accurate portrayal of only the constraints provided by the evidence in hand).

What the Wikipedia entry calls the "Great Oxygenation Event" is the initial appearance of free oxygen in Earth atmosphere some 2.4 billion years ago.

The paper we're discussing, "Oxygen requirements of the earliest animals", is about the Ediacaran period, 635 to 542 million years ago, when oxygen level in the oceans were increasing to a new level, and a range of multicelled animals appear in the fossil record.

Two different periods of evolutionary history, almost two billion years apart.

The new paper is a significant piece of scientific work, and I'm glad that you brought it to our attention. But it does not contradict what the WP entry says about the first mitochondria.

Paul Wally
2014-Feb-21, 11:51 AM
What isn't ruled out, is that both animals and their mitochondria-based aerobic respiration capabilities, could also have existed prior to the GOE, (as is now revealed by the test). The Wiki article completely overlooks this as a possibility, which is highly misleading.

"Could have existed" and "could have evolved" are two different issues. Just because a modern day organism adapted to certain extraordinary conditions, doesn't mean that it is possible for it to have evolved prior to the so called GOE. Besides, there's no evidence in the fossil record as far as we know, so this is just another unconfirmed hypothesis. Therefore, there's no reason why the Wikipedia article should pay any more attention to this than to countless other unconfirmed hypotheses.

swampyankee
2014-Feb-21, 08:18 PM
This is not a complete surprise to anybody: anaerobic eukaryotes have been known about and studied for a while (see, among others, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2606767/, http://www.ncbi.nlm.nih.gov/pubmed/22688819, http://www.ncbi.nlm.nih.gov/pubmed/20370917)

publiusr
2014-Feb-21, 10:53 PM
"Well, the sooner we can kick this nasty oxygen habit, the sooner we can get out in space--right COPD sufferers?

Cough, hack

"Aw--give it up, you don't need oxygen, you've done so well on Chesterfields."

Swift
2014-Feb-28, 06:03 PM
Maybe nitrogen was the trigger, not oxygen

From Laboratory Equipment (http://www.laboratoryequipment.com/news/2014/02/nitrogen-may-have-caused-great-leap-forward-ocean-life?et_cid=3795479&et_rid=54636800&type=headline)


It has long been believed that the appearance of complex multicellular life towards the end of the Precambrian (the geologic interval lasting up until 541 million years ago) was facilitated by an increase in oxygen, as revealed in the geological record. However, it has remained a mystery as to why oxygen increased at this particular time and what its relationship was to “Snowball Earth” – the most extreme climatic changes the Earth has ever experienced – which were also taking place around then.

This new study shows that it could in fact be what was happening to nitrogen at this time that helps solve the mystery.

The researchers, led by Patricia Sanchez-Baracaldo of the Univ. of Bristol, used genomic data to reconstruct the relationships between those cyanobacteria whose photosynthesis in the open ocean provided oxygen in quantities sufficient to be fundamental in the development of complex life on Earth.

Some of these cyanobacteria were also able to transform atmospheric nitrogen into bioavailable nitrogen in sufficient quantities to contribute to the marine nitrogen cycle, delivering nitrogen fertilizer to the ecosystem. Using molecular techniques, the team were able to date when these species first appeared in the geological record to around 800 million years ago.

Sanchez-Baracaldo says, "We have known that oxygenic photosynthesis – the process by which microbes fix carbon dioxide into carbohydrates, splitting water and releasing oxygen as a by-product – first evolved in freshwater habitats more than 2.3 billion years ago. But it wasn’t until around 800 million years ago that these oxygenating cyanobacteria were able to colonize the vast oceans (two thirds of our planet) and be fertilized by enough bioavailable nitrogen to then produce oxygen – and carbohydrate food – at levels high enough to facilitate the next ‘great leap forward' towards complex life. Our study suggests that it may have been the fixing of this nitrogen fertilizer in the oceans at this time that played a pivotal role in this key moment in the evolution of life on Earth."


The paper is in Current Biology (http://www.cell.com/current-biology/abstract/S0960-9822(14)00074-8); here is the abstract:

The Neoproterozoic (1000542 million years ago, Mya) was characterized by profound global environmental and evolutionary changes, not least of which included a major rise in atmospheric oxygen concentrations [1,2], extreme climatic fluctuations and global-scale glaciation [3], and the emergence of metazoan life in the oceans [4,5]. We present here phylogenomic (135 proteins and two ribosomal RNAs, SSU and LSU) and relaxed molecular clock (SSU, LSU, and rpoC1) analyses that identify this interval as a key transition in the marine nitrogen cycle. Specifically, we identify the Cryogenian (850635 Mya) as heralding the first appearance of both marine planktonic unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing picocyanobacteria (Synechococcus and Prochlorococcus [6]). Our findings are consistent with the existence of open-ocean environmental conditions earlier in the Proterozoic adverse to nitrogen-fixers and their evolutionspecifically, insufficient availability of molybdenum and vanadium, elements essential to the production of high-yielding nitrogenases. As these elements became more abundant during the Cryogenian [7,8], both nitrogen-fixing cyanobacteria and planktonic picocyanobacteria diversified. The subsequent emergence of a strong biological pump in the ocean implied by our evolutionary reconstruction may help in explaining increased oxygenation of the Earths surface at this time, as well as tendency for glaciation.

Swift
2014-Oct-31, 03:06 PM
More data on the oxygen concentration question

R&D Magazine (http://www.rdmag.com/news/2014/10/lack-oxygen-delayed-appearance-animals-earth?et_cid=4239537&et_rid=54636800&location=top)


Geologists are letting the air out of a nagging mystery about the development of animal life on Earth.

Scientists have long speculated as to why animal species didn’t flourish sooner, once sufficient oxygen covered the Earth’s surface. Animals began to prosper at the end of the Proterozoic period, about 800 million years ago—but what about the billion-year stretch before that, when most researchers think there also was plenty of oxygen?

Well, it seems the air wasn’t so great then, after all.

In a study published Oct. 31 in Science, Yale researcher Noah Planavsky and his colleagues found that oxygen levels during the “boring billion” period were only 0.1% of what they are today. In other words, Earth’s atmosphere couldn’t have supported a diversity of creatures, no matter what genetic advancements were poised to occur.

“There is no question that genetic and ecological innovation must ultimately be behind the rise of animals, but it is equally unavoidable that animals need a certain level of oxygen,” said Planavsky, co-lead author of the research along with Christopher Reinhard of the Georgia Institute of Technology. “We’re providing the first evidence that oxygen levels were low enough during this period to potentially prevent the rise of animals.”

The scientists found their evidence by analyzing chromium (Cr) isotopes in ancient sediments from China, Australia, Canada, and the United States. Chromium is found in the Earth’s continental crust, and chromium oxidation is directly linked to the presence of free oxygen in the atmosphere.

Specifically, the team studied samples deposited in shallow, iron-rich ocean areas, near the shore. They compared their data with other samples taken from younger locales known to have higher levels of oxygen.

Oxygen’s role in controlling the first appearance of animals has long vexed scientists. “We were missing the right approach until now,” Planavsky said. “Chromium gave us the proxy.” Previous estimates put the oxygen level at 40% of today’s conditions during pre-animal times, leaving open the possibility that oxygen was already plentiful enough to support animal life.

In the new study, the researchers acknowledged that oxygen levels were “highly dynamic” in the early atmosphere, with the potential for occasional spikes. However, they said, “It seems clear that there is a first-order difference in the nature of Earth surface Cr cycling” before and after the rise of animals.

Githyanki
2014-Nov-09, 12:59 AM
Are plants considered complex life? If they are, no.

For intelligent life as we know it, yes.

Colin Robinson
2014-Nov-09, 08:17 PM
Are plants considered complex life? If they are, no.

For intelligent life as we know it, yes.

The term "complex life" can mean just about anything... But the opening post of this thread is about sea sponges, which are among the oldest classes of multi-celled animals.