Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
4 online now:
Newest Member: popoi
Post Volume: Total: 915,817 Year: 3,074/9,624 Month: 919/1,588 Week: 102/223 Day: 0/13 Hour: 0/0


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Are there evolutionary reasons for reproduction?
Nij
Member (Idle past 4890 days)
Posts: 239
From: New Zealand
Joined: 08-20-2010


Message 121 of 136 (577022)
08-26-2010 10:08 PM
Reply to: Message 119 by barbara
08-26-2010 9:51 AM


Re: Look Ma, no enzymes oxygen!
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.

This message is a reply to:
 Message 119 by barbara, posted 08-26-2010 9:51 AM barbara has replied

Replies to this message:
 Message 127 by barbara, posted 09-09-2010 10:01 AM Nij has not replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 122 of 136 (577090)
08-27-2010 6:50 AM
Reply to: Message 114 by dennis780
08-20-2010 10:59 PM


Re: Look Ma, no enzymes!
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.

This message is a reply to:
 Message 114 by dennis780, posted 08-20-2010 10:59 PM dennis780 has not replied

Replies to this message:
 Message 123 by barbara, posted 09-08-2010 4:04 PM Dr Jack has replied

  
barbara
Member (Idle past 4802 days)
Posts: 167
Joined: 07-19-2010


Message 123 of 136 (580315)
09-08-2010 4:04 PM
Reply to: Message 122 by Dr Jack
08-27-2010 6:50 AM


Re: Look Ma, no enzymes!
This is the biggest question I wish someone could answer. Oxygen being so toxic for early life should have stop the ones producing it.

This message is a reply to:
 Message 122 by Dr Jack, posted 08-27-2010 6:50 AM Dr Jack has replied

Replies to this message:
 Message 124 by Wounded King, posted 09-08-2010 5:09 PM barbara has not replied
 Message 125 by Taq, posted 09-08-2010 5:35 PM barbara has replied
 Message 128 by Dr Jack, posted 09-09-2010 8:10 PM barbara has not replied
 Message 129 by DC85, posted 09-17-2010 10:12 PM barbara has replied

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 124 of 136 (580322)
09-08-2010 5:09 PM
Reply to: Message 123 by barbara
09-08-2010 4:04 PM


Re: Look Ma, no enzymes!
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

This message is a reply to:
 Message 123 by barbara, posted 09-08-2010 4:04 PM barbara has not replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.7


Message 125 of 136 (580324)
09-08-2010 5:35 PM
Reply to: Message 123 by barbara
09-08-2010 4:04 PM


Re: Look Ma, no enzymes!
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.

This message is a reply to:
 Message 123 by barbara, posted 09-08-2010 4:04 PM barbara has replied

Replies to this message:
 Message 126 by barbara, posted 09-09-2010 9:29 AM Taq has not replied

  
barbara
Member (Idle past 4802 days)
Posts: 167
Joined: 07-19-2010


Message 126 of 136 (580478)
09-09-2010 9:29 AM
Reply to: Message 125 by Taq
09-08-2010 5:35 PM


Re: Look Ma, no enzymes!
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.

This message is a reply to:
 Message 125 by Taq, posted 09-08-2010 5:35 PM Taq has not replied

  
barbara
Member (Idle past 4802 days)
Posts: 167
Joined: 07-19-2010


Message 127 of 136 (580480)
09-09-2010 10:01 AM
Reply to: Message 121 by Nij
08-26-2010 10:08 PM


Re: Look Ma, no enzymes oxygen!
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?

This message is a reply to:
 Message 121 by Nij, posted 08-26-2010 10:08 PM Nij has not replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 128 of 136 (580544)
09-09-2010 8:10 PM
Reply to: Message 123 by barbara
09-08-2010 4:04 PM


Re: Look Ma, no enzymes!
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.

This message is a reply to:
 Message 123 by barbara, posted 09-08-2010 4:04 PM barbara has not replied

  
DC85
Member (Idle past 380 days)
Posts: 876
From: Richmond, Virginia USA
Joined: 05-06-2003


Message 129 of 136 (581879)
09-17-2010 10:12 PM
Reply to: Message 123 by barbara
09-08-2010 4:04 PM


Re: Look Ma, no enzymes!
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.

This message is a reply to:
 Message 123 by barbara, posted 09-08-2010 4:04 PM barbara has replied

Replies to this message:
 Message 130 by barbara, posted 09-18-2010 6:35 AM DC85 has not replied

  
barbara
Member (Idle past 4802 days)
Posts: 167
Joined: 07-19-2010


Message 130 of 136 (581920)
09-18-2010 6:35 AM
Reply to: Message 129 by DC85
09-17-2010 10:12 PM


Re: mammal placenta
New question: Did the retrovirus that form the placenta the same in all mammals that have a placenta?

This message is a reply to:
 Message 129 by DC85, posted 09-17-2010 10:12 PM DC85 has not replied

Replies to this message:
 Message 131 by Dr Jack, posted 09-18-2010 6:55 AM barbara has replied

  
Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 131 of 136 (581921)
09-18-2010 6:55 AM
Reply to: Message 130 by barbara
09-18-2010 6:35 AM


Re: mammal placenta
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.

This message is a reply to:
 Message 130 by barbara, posted 09-18-2010 6:35 AM barbara has replied

Replies to this message:
 Message 132 by barbara, posted 10-06-2010 6:58 AM Dr Jack has not replied

  
barbara
Member (Idle past 4802 days)
Posts: 167
Joined: 07-19-2010


Message 132 of 136 (585151)
10-06-2010 6:58 AM
Reply to: Message 131 by Dr Jack
09-18-2010 6:55 AM


Re: mammal placenta
How do you know it only happened once?

This message is a reply to:
 Message 131 by Dr Jack, posted 09-18-2010 6:55 AM Dr Jack has not replied

Replies to this message:
 Message 133 by caffeine, posted 10-06-2010 7:28 AM barbara has replied

  
caffeine
Member (Idle past 1025 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 133 of 136 (585152)
10-06-2010 7:28 AM
Reply to: Message 132 by barbara
10-06-2010 6:58 AM


Re: mammal placenta
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.

This message is a reply to:
 Message 132 by barbara, posted 10-06-2010 6:58 AM barbara has replied

Replies to this message:
 Message 134 by barbara, posted 10-06-2010 7:53 AM caffeine has replied

  
barbara
Member (Idle past 4802 days)
Posts: 167
Joined: 07-19-2010


Message 134 of 136 (585153)
10-06-2010 7:53 AM
Reply to: Message 133 by caffeine
10-06-2010 7:28 AM


Re: mammal placenta
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?

This message is a reply to:
 Message 133 by caffeine, posted 10-06-2010 7:28 AM caffeine has replied

Replies to this message:
 Message 135 by caffeine, posted 10-11-2010 5:09 AM barbara has not replied

  
caffeine
Member (Idle past 1025 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 135 of 136 (586099)
10-11-2010 5:09 AM
Reply to: Message 134 by barbara
10-06-2010 7:53 AM


Re: mammal placenta
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.

This message is a reply to:
 Message 134 by barbara, posted 10-06-2010 7:53 AM barbara has not replied

Replies to this message:
 Message 136 by Wounded King, posted 10-11-2010 5:55 AM caffeine has seen this message but not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024