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Author | Topic: Are there evolutionary reasons for reproduction? | |||||||||||||||||||||||||||||||
Nij Member (Idle past 4920 days) Posts: 239 From: New Zealand Joined: |
Water is made of 90% oxygen so how could it be that there was no oxygen in early earth?
Because the vast majority of oxygen was stuck in things like water and carbon dioxide. There was very little if any atmospheric oxygen, meaning oxygen in the form of O2(g). We started with an atmosphere of lots of carbon dioxide, and very little if any oxygen gas - we can see this from the effects of atmospheric oxygen on things like iron and uranium deposits (because oxygen oxidises iron, and it allows water solubility and thereby transfer of uranium; neither occurs until a certain point in the geological record). Once "plants" got reasonably established, they started to convert that carbon dioxide to oxygen. That equivocation on what is meant by "oxygen" is what may have confused you there, I think.
The water at the deep vents does not have oxygen. How does this make sense?
As jar pointed out, it doesn't. The water at the deep vents has oxygen, just like water everywhere. Thing is, it's dissolved at somewhat low levels. Hence the mammal inability to breathe water, and why fish use gills. But this amount is sufficient for many reactions to take place over time, and hence there is no problem from the abiogenesis angle. Edited by Nij, : No reason given.
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 9.2 |
Why do you think oxygen is needed? It's widely thought that oxygen based metabolism didn't evolve until quite late in the history of life, sulfur-based metabolism (which still exists today) is a much more likely candidate for the metabolism of early life, but there are many other possibilities.
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barbara Member (Idle past 4832 days) Posts: 167 Joined: |
This is the biggest question I wish someone could answer. Oxygen being so toxic for early life should have stop the ones producing it.
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Wounded King Member Posts: 4149 From: Cincinnati, Ohio, USA Joined: |
Hasn't this exact question been answered for you just a post or two ago?
You need to learn that oxygen atoms behave differently in different molecular compounds. Not all oxygen species are as reactive as each other. Atmospheric oxygen tends to have more reactive species due to ionising radiation. As has been pointed out the prebiotic earth essentially had no atmospheric oxygen and water is quite effective at attenuating ionising radiation. So there would not be a high proportion of toxic reactive oxygen species. To some extent this also depends on the exact abiogenesis scenario you are discussing as deep sea vents are obviously even more protected while a surface pool scenario might allow a substantial exposure to ionising radiation but may not consist principally of water. It is also worth noting that a number of proposed abiogenetic pathways rely on ionising radiation, in the form of UV, for certain reactions to occur. TTFN, WK
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Taq Member Posts: 10085 Joined: Member Rating: 5.6 |
This is the biggest question I wish someone could answer. Oxygen being so toxic for early life should have stop the ones producing it. Unless, of course, if the oxygen producers were tolerant of free oxygen. The advent of photosynthesis occurred well after the beginning of life. On top of that, there are still obligate anaerobes that find niches to fill in our oxygen rich world. In fact, you can find a few of them in your gut right now.
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barbara Member (Idle past 4832 days) Posts: 167 Joined: |
According to a recent genetic study the biomarker for the first cyanobacteria and the first eukaryote is 2.7 Ga. However, the first eukaryote did not have mitochondria until after the oxygen crisis occurred and this was 1.8 Ga.
It is known today that cyanobacteria do not have a problem with living in their own waste production. It has not been determined if this was always the case since its first appearance. Edited by barbara, : No reason given.
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barbara Member (Idle past 4832 days) Posts: 167 Joined: |
Once plants got reasonably established is why oxygen was able to build up in the atmosphere?
Plant cells resemble colonies of cyanobacteria and plants have mitochondria cells for respiration. This makes it more interesting since the first cyanobacteria and the first eukaryote without mitochondria originated at the same time. Are you saying that cyanobacteria could not by itself produce the oxygen that we depend on today? Ocean plants that are eukaryotes with mitochondria and chloroplasts is why we have an o2 environment?
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 9.2 |
They did what all organisms do with their waste products, excreted them into the environment. Oxygen, conveniently is a gas and thus doesn't build up locally in the same way as most excreted toxins.
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DC85 Member Posts: 876 From: Richmond, Virginia USA Joined: |
Oxygen being so toxic for early life should have stop the ones producing it. It was... It's thought many early life forms went extinct after large amounts of Oxygen became a large part of the atmoshere. It only takes a few survivors.
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barbara Member (Idle past 4832 days) Posts: 167 Joined: |
New question: Did the retrovirus that form the placenta the same in all mammals that have a placenta?
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 9.2 |
New question: Did the retrovirus that form the placenta the same in all mammals that have a placenta? That's not really on-topic here. Start a new thread if you want to ask more. But, quickly: the placental mammals (eutheria) appear to all share the same gene derived from a retrovirus that is involved in placental formation. This implies that the insertion happened once for all placental mammals. Certain marsupials have very placenta like structures, that appear to be separately evolved; I do not know whether these share the same genetic basis.
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barbara Member (Idle past 4832 days) Posts: 167 Joined: |
How do you know it only happened once?
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caffeine Member (Idle past 1055 days) Posts: 1800 From: Prague, Czech Republic Joined: |
How do you know it only happened once? Because the only other possibility is that a retrovirus inserted itself into one little mammal's genome, where it became involved in placental formation; and then coincientally the same sort of retrovirus inserted itself into a different mammal's genome, in the same place, and became involved in placental formation as well. The same event happening twice, in such specific detail, at about the same time, is far less intrinsically likely than it happening once. Unless there's some special reason to opt for such an unlikely event, it makes more sense to assume it happened just the once.
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barbara Member (Idle past 4832 days) Posts: 167 Joined: |
Since it only occurred once and you are sure of it then is there a tree diagram linking all species that have placenta formation of this identical retrovirus sequence?
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caffeine Member (Idle past 1055 days) Posts: 1800 From: Prague, Czech Republic Joined: |
Since it only occurred once and you are sure of it then is there a tree diagram linking all species that have placenta formation of this identical retrovirus sequence? Sorry for the big delay in replying - I've been away. I'm not really sure what you mean. Are you asking for a tree of placental mammals? Or a tree based specifically on this one gene. If the latter, then I don't know, but trying to work out relationships on one gene is a bad way of doing things. Odd little things could happen to an individual gene over the course of the millenia that give strange answers. if you want a robust tree of relationships within a group, you need to use lots of genes together, to avoid getting thrown off by exceptions. Think about if you were trying to work out how tall people are. If you solved this question by looking at one individual then you might wind up with a hopelessly wrong answer. This person could be a midget, or a towering giant, and your estimate of the average would be miles off.
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