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Evidence suggests that life appeared very soon after the Earth formed. Right. This means that life can form easily. OK so far. But

if life formed so easily, why has it appeared only once in Earth's history? :confused:

 

Surely, if it can be produced easily, it should have come up in several places in various forms and the descendants of each life strand would somehow have left evidence of their existence. But there is only evidence of the current life.

 

The only 2 things I can suggest are that:

 

1) Life appeared at the beginning in many ways and many places on the primordial Earth, but only the current one was selected by evolution. Which then would suggest that the conditions at the time of the birth of life were so alien to what we see now anywhere on the Earth that only 1 strand managed to evolve quickly enough to stay around until the present day.

 

It also means that not a single one of the different environments on Earth today are good enough to produce life from inert material, otherwise there would be places on Earth where life comes up from non-living stuff all the time.

 

So what is it likely to take to make life from inert material? Where else in our solar system could we find these conditions? How likely would these conditions be found in other stellar systems?

 

2) Life appeared in many chemical forms, but somehow all had in common the cellular structure and the ATGCU bases of RNA, which were the sine qua non of what turns inert stuff into living structures. This would imply that if life is found somewhere else in the Universe, it would also use the same stuff and basic structure as "our life", and would be not-so-alien to us. Is there really nothing else that could yield life?

 

So, to conclude:

Am I missing something? Have scientists already managed to answer part of my Question? Has anyone ever asked my Question?

Edited by Aitor
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I think the assumptions that "life can form easily" and that it "appeared only once in Earth's history" are sloppy ones, but to answer your question, early life had a much different field to compete on. Perhaps life has tried to form many times throughout the ages but has merely been eaten or supplanted by the current overwhelming amount of life forms that have evolved to fill the various niches in the ecosystems.

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SOrry for having made my question unclear.

 

My question is:

"If life formed so early in the history of the Earth, thereby implying that it was a more likely event than we think, how come we see only evidence of 1 type of life on the Earth? Why does the tree of life only trace life's history only to one primordial life form? Why aren't there more trees of life?"

 

Are the above questions clarifying my original question?

 

Thanks for your contributions already. They are very pertinent and I am happy to accept them as valid answers. :)

 

Anybody would know of (likely very recent) research about potential life-creating chemical systems different from ours?

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Galindo, it's not what I mean by tree of life. Evolution transforms species into others. Ultimately, the primordial organisms yield a vast array of new species that are completely different from each other. However, they remain related, because their fundamental building blocks and inner workings are exactly the same.

 

Tracking the evolution of the complexity of these inner workings in reverse brings one back to just one primordial ancestor to all current living things, were they a tree, a leopard, a human, a bacterium, a virus, a archaeum, or a slime. This is the root of just one tree of life. No other parallel life structure is observable on Earth.

 

Actually, could prions be part of that hypothetical other tree of life? One wonders...

 

Come on, geneticists and biologists and paleontologists out there! I need your contributions!

 

Thanks in advance.

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Well, isn't there more than just 1 type of life on Earth. I mean trees are much different from cats, which are much different from fish...etc.

And yet they all share common parts of the DNA, suggesting a common ancestor to all of life on Earth.

 

 

Aitor, your basic premise is a bit weird. Why do you assume life formed "so easily" on Earth? The fact that life formed doesn't mean it was an easy process, and if it wasn't one, that would explain why it only happened once. It seems you are assuming the process is easy, when it isn't necessarily so.

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What's the problem with multiple origins, all but one dying out?

 

There was more than one ancestral human at any given point in time, but all living humans descend from a single female that lived 200,000 years ago. Other women at the time had kids, but eventually, the lines died out.

 

Why is this unbelievable for the origin(s) of life?

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In addition, it is possible that once a given life form (the current) has established itself, it rapidly filled available niches and created conditions unfavorable for new forms of life to establish themselves. There are some physicists (well, one at least) that argue that it is likely there may be more life around that actually is not based on DNA and that we only fail to see it because biologists are too stupid to find non-DNA based life forms. However, there is no evidence for that.

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......... but all living humans descend from a single female that lived 200,000 years ago. Other women at the time had kids, but eventually, the lines died out.

.....

 

 

Sorry my friend, but I don´t understand this affirmation. Are you suggesting that somewhere in time (200.000 years ago), there was a human being capable to reproduce itself, without the participation of a partner of the opposite sex , and its offspring continued reproducing through the rest of time, without the mixing of its genetic pool with the rest of the human beings that existed at a given time ? (kind of a way out of proportion inbreeding).:eek:

 

It doesn´t make sense.

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Sorry my friend, but I don´t understand this affirmation. Are you suggesting that somewhere in time (200.000 years ago), there was a human being capable to reproduce itself, without the participation of a partner of the opposite sex , and its offspring continued reproducing through the rest of time, without the mixing of its genetic pool with the rest of the human beings that existed at a given time ? (kind of a way out of proportion inbreeding).:eek:

 

It doesn´t make sense.

 

https://genographic.nationalgeographic.com/genographic/lan/en/atlas.html

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Sorry my friend, but I don´t understand this affirmation. Are you suggesting that somewhere in time (200.000 years ago), there was a human being capable to reproduce itself, without the participation of a partner of the opposite sex , and its offspring continued reproducing through the rest of time, without the mixing of its genetic pool with the rest of the human beings that existed at a given time ? (kind of a way out of proportion inbreeding).:eek:

 

It doesn´t make sense.

 

Hehe. No. Mokele is talking about this:

 

http://en.wikipedia.org/wiki/Mitochondrial_Eve

 

It's not that other people didn't contribute their genetics, it's that from this person there is an unbroken matrilineal line (mother to maternal grandmother to maternal great grandmother, etc.) to every single person currently alive on Earth. Read the "common fallacies" section in the linked article for clarification.

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1) Life appeared at the beginning in many ways and many places on the primordial Earth, but only the current one was selected by evolution. Which then would suggest that the conditions at the time of the birth of life were so alien to what we see now anywhere on the Earth that only 1 strand managed to evolve quickly enough to stay around until the present day.

 

All it would suggest, was that one life form was able to out-compete all the others (if there were others, which does seem a reasonable assumption). It doesn't mean the environment had to kill off the others, just that the one we are descended from either killed, ate, or ate the food of, all other life forms.

 

As I understand it, there was plenty useful chemicals on earth before life, but of course those would rapidly get eaten, and any life that depended on them would then die out -- as would the possibility for new life to form from them.

 

New life forms now, from what is available -- modern life forms. Of course, that means they won't be drastically different from us.

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Right, so a different kind of life is not prevented from appearing at any time, providing there are resources for it and the right conditions. The Earth is a pretty diverse place, and where our type of life cannot exist, there must therefore be a niche for another type. Why aren't we observing this?

 

As for my assertion that making life is easy, it comes from our knowledge that fossilised remains of bacterial activity were found in a rock 3.8 billion years old somewhere on this planet (my memory is failing on that location detail), but at that time Earth was a pretty nasty place to be and it had just about managed to cool down enough to have primitive shallow oceans with volcanoes and gashes gushing lava everywhere, and an unbelievably violent and lethal meteorite shower lasting a few million years had just about started to decline. Basically, the Earth was so dangerous that nothing would be able to survive on it, and yet, life had already started to leave its trace as carbonates, which we can see today.

 

Which is why I said that life-creation must be relatively easy since in the worst possible environment it still appeared and thrived.

 

With the much more tame conditions nowadays, it should therefore be dead easy to create life (pun intended because it is silly) anywhere, one would think, especially where our type of life has not managed to set a foothold thereby leaving resources intact for something else to emerge and thrive on.

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Right, so a different kind of life is not prevented from appearing at any time, providing there are resources for it and the right conditions. The Earth is a pretty diverse place, and where our type of life cannot exist, there must therefore be a niche for another type. Why aren't we observing this?

 

Again, how do you know that there is not any new life arising, and simply being eaten by life forms that have had billions of years to evolve? How can you tell?

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Again, how do you know that there is not any new life arising, and simply being eaten by life forms that have had billions of years to evolve? How can you tell?
I also wondered why this explanation wasn't enough to satisfy the OP early on in the thread. Bacteria is ubiquitous. It lives where more complicated life can't.
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Actually we don't know if other life forms share our planet with us. it's pretty obvious that complex life can all be traced to a common ancestor but something very few people know is that when we search for life forms on the earth as in bacteria we only search for life like us. The tests we use cannot detect life that is not like us.

 

http://discovermagazine.com/2007/jul/aliens-among-us

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My apologies to Mokele, for my post which could have been taken as a mock (although it never was), and my thanks to Sisyphus and Jayhawker, who really helped me to understand Mokele`s post by clarifing the concept, that I didn´t understand at the moment, sincerely. :embarass:

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With the much more tame conditions nowadays, it should therefore be dead easy to create life (pun intended because it is silly) anywhere, one would think, especially where our type of life has not managed to set a foothold thereby leaving resources intact for something else to emerge and thrive on.

 

The last part is the problem - Earth is full. *Everywhere* has life, even in the most extreme conditions. Thus, anywhere there are the complex molecules that could lead to life, there's already-living organisms who'll eat them up.

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My point precisely.

 

Moontaman, this is the physicist I am talking about. There a lot of counterarguments. Too many to name them all, however even if there was a life-form totally different from us, there should be evidence of their metabolic activity. Yet what happens on earth can readily attributed to existing organism. In other words, even if we do not focus on DNA or even carbon as basis, there is no evidence that are different organisms doing anything. It boils down to plain chemistry.

This is one of the cases when someone tries to make assumptions way out of their field of expertise.

Edited by CharonY
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however even if there was a life-form totally different from us, there should be evidence of their metabolic activity. Yet what happens on earth can readily attributed to existing organism. In other words, even if we do not focus on DNA or even carbon as basis, there is no evidence that are different organisms doing anything. It boils down to plain chemistry.

 

I don't believe it. I've heard of species, such as pfiesteria piscicida, described as a phantom. This critter, as I understand it, was only discovered because it kept killing off the fish, and the scientists had no idea what was causing it. Eventually they looked really carefully and found this critter. I suspect this species would still be unknown if it did not kill fish.

 

We have enough trouble as it is finding life like us (DNA based), so why would it be so hard to believe we would have trouble finding life unlike us right at our doorstep? Metabolic activity, sure, but that would only work if it were alone. There's plenty of bacteria everywhere which would be given the credit for metabolic activity.

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