second genesis

[nudger1964]

This is nothing to do with religion.
Knowing nothing about biology, I am interested in in hearing from those wiser than I, whether it is reasonably possible to distinguish between two separate genesis of life on earth.
The science will probably go over my head, but taking the fossil record back as far as we can go, to the most primitive life we know is our origin"¦.if there was a primitive independent genesis, would you expect to be able to tell?
Im guessing not from fossil records"¦so how about with extremophiles or such like. I know there was some talk about arsenic bacteria a while back, which seems to have been discounted now.

if they were to find microbes on mars, how would you go about demonstrating they had indepenent origin

 

[Inferno]

First of all, the "arsenic bacteria". PZ Myers of Pharyngula has dealt with this issue: It's a bacteria that lives in an arsenic rich environment, it is NOT an arsenic based life form.

As for different genesis', here's my take: There's only been one on Earth. We'd not know about it from the fossil record and we wouldn't know about it from extremophiles, we'd simply know about it from DNA, or rather what that other life form uses in stead of DNA. If there was such an event, we'd expect the very fundamentals to be somewhat different to ours. I at least would expect it to not be a DNA based life form, because that would be just too lucky. If there was such an event, it would be noticed here, at the "blueprint" level.
As such, I'm fairly certain that it hasn't happened yet or that we have yet to find it.

 

[nudger1964]

hmm, the problem with that though, isnt it right to say that our DNA life didnt just suddenly arrive, it probably came from RNA.
if so, would you expect to be able to trace our DNA life back into RNA life, and distinguish it from a seperate RNA life...
or is that just meaningless drivle

 

[Inferno]

Yes, our life probably emerged from RNA based life. What's to say though that this other life form will use DNA or RNA? Maybe there's some form that we don't know about. Maybe it incorporates different proteins. Or maybe there's something completely different that's changed. Maybe it doesn't use water, but instead sulfur or silicone.

That's really the point: If this other genesis of life is indistinguishable from ours and even fits the evolutionary tree (both incredibly unlikely events) then there's no way to find out and as such not really an interesting question. If there is some difference, then we haven't found it yet and I wouldn't know what to look for, except to suggest that the difference must lie at the fundamentals, whatever those differences may be.

 

[nudger1964]

well yeah thats what i am trying to see if it would be possible to seperate independent events going back to our best hypothesis of how it started, which seems to be RNA.
obviously if you had completely different chemestry that would make it easy (i think phosphorous has been proposed as a possible).
this is kinda what the whole field of astrobiology is trying to look at...i wouldnt say it is uninteresting.

take this hyperthetical.
RNA is the common starting mechanism for carbon based life. We assume we had an RNA genesis event here on earth, we find an RNA genesis on Mars (just makes it easier to use a different planet). We have no record of earths RNA life, but we have a bottle of Martian RNA life.
would you expect to be able to prove they were independent....thats the question in a nutshell

 

[Inferno]

Again, the point I tried to make is this: If there is a difference, it has to be a fundamental one. I'd expect the differences to be greater for an alien life form because they had to adapt to a different environment.
So yes, we probably would be able to tell, because if the fundamentals are similar then there's a good chance that it's descended from the same stock.

 

[Unwardil]

What I think would be the most difficult to trace in the fossil record is if, say, there were several origin point of life on earth more or less simultaneous but separated and isolated. When they met, however, it is likely that only 1 would be the dominant one eventually wiping all the others out, hence the reason that all life on earth is descended from a single source. That doesn't mean that at some time in the history of life there weren't several types of life each with their own unique abiogenical origins, it only means that only 1 of them ultimately made it.

Which is a fine and dandy thing to theorize, but I don't know how you'd go about proving it.

 

[Visaki]

There might have been more than one abiogenesis events but it's very hard to get any solid evidence about it. This is because it's quite possible that life was wiped out many times in the volatile early Earth before cataclysmic events became rare enough for life to spread (not many fossils of microbes survive if the whole crust of Earth is melted by an impact). Also as I understand it horisontal genetransfer would wipe out evidence of different abiogenesis events in the case life developed many times with pretty much the same template (not that unlikely when you get to the chemistry of it) and about the same time.

I read a pretty good book about early life this winter. It theorized that life might have actually started deep (some kilometers) within the crust of the planet where it'd be safe from all but the most violent impact events on early Earth. I also seems that some of the most weird living things today, bacteria which live in extreme conditions and which live deep within the Earth, might actually be the most unlike other life. This suggests that not only they diverged from other forms of life very early, but also that it's the other forms of life diverged from them which would mean they are closer to the original lifeforms of Earth than, lets say, "normal" bacteria.

Abiogenesis events might even be happening these days. It's just that older life would probably see this new one as food and eat them away before they have the time to adapt to more robust, uneatable, configuration.

 

[nudger1964]

There might have been more than one abiogenesis events but it's very hard to get any solid evidence about it. This is because it's quite possible that life was wiped out many times in the volatile early Earth before cataclysmic events became rare enough for life to spread (not many fossils of microbes survive if the whole crust of Earth is melted by an impact). Also as I understand it horisontal genetransfer would wipe out evidence of different abiogenesis events in the case life developed many times with pretty much the same template (not that unlikely when you get to the chemistry of it) and about the same time.
I read a pretty good book about early life this winter. It theorized that life might have actually started deep (some kilometers) within the crust of the planet where it'd be safe from all but the most violent impact events on early Earth. I also seems that some of the most weird living things today, bacteria which live in extreme conditions and which live deep within the Earth, might actually be the most unlike other life. This suggests that not only they diverged from other forms of life very early, but also that it's the other forms of life diverged from them which would mean they are closer to the original lifeforms of Earth than, lets say, "normal" bacteria.

Abiogenesis events might even be happening these days. It's just that older life would probably see this new one as food and eat them away before they have the time to adapt to more robust, uneatable, configuration.

the highlighted text was the kinda thing i was asking about, thanks for that.
The rest, i agree with every word.
Sure its difficult, but that shouldnt stop us looking right? This is after all the big question.
Hopefully astrobiology as a field of science will mature and push forward our understanding of life on early earth.
A few yrs ago it was generally thought life started after the late heavy bombardment. Now it is generally thought it survived it because of the very short period from it to where we know life started. Every little bit of information is important to our understanding.

 

[Laurens]

This is nothing to do with religion.
Knowing nothing about biology, I am interested in in hearing from those wiser than I, whether it is reasonably possible to distinguish between two separate genesis of life on earth.
The science will probably go over my head, but taking the fossil record back as far as we can go, to the most primitive life we know is our origin"¦.if there was a primitive independent genesis, would you expect to be able to tell?
Im guessing not from fossil records"¦so how about with extremophiles or such like. I know there was some talk about arsenic bacteria a while back, which seems to have been discounted now.

if they were to find microbes on mars, how would you go about demonstrating they had indepenent origin

We can't tell for certain that life didn't originate more than once on this planet. What we can tell from analysis of DNA and other biochemical factors such as proteins, amino acids etc. is that all life currently inhabiting Earth is descended from a common ancestor.

If we found life on Mars, a pretty good indicator of independent origin would be the aforementioned biochemistry. If it used different amino acids, or had a different genetic code, we could say with reasonable certainty that this life resulted from an independent origin.