If we were to find a primordial sea on an earthlike planet what would the first forms of life be? Would they be plant or animal? On Earth was there a branch off from one to the other. Is there a name or terminology for this branch off of the tree of life so to speak?

Why is this in ATM? Your questions look like perfectly orthodox questions about hypothetical primordial biology.

My best guess is that the earliest living things would be something resembling bacteria. I do not know when or where early multicellular organisms diverged into what we now know as plants and animals.

They are called Archea they and bacteria were first. They still exist.

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

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Well, their descendents exist, and have evolved so much that we are not really sure exactly what the first organisms were like.

However, we can make some deductions based on what we do know. The first organisms would be either photosynthetic or chemotrophic - that is, thay will derive their energy either from sunlight or from chemistry in a manner similar to what we find around "black smokers" (Wiki article here). Other organisms could then evolve from these that prey on these organisms.

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The first forms of life might not even be cells. They might be concentrations of organic reactions occurring in localised areas, perhaps trapped in certian types of clay-like minerals.
Later there could be things called protobionts, cell-like bubbles filled with reacting organic material forming a primitive metabolism; the surface of the bubble could be formed from lipids.
Here is Wiki on protobionts;
http://en.wikipedia.org/wiki/Protobionts
here is a page with a picture of a hypothetical protobiont
http://biocab.org/Protobiont.html

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Another interesting form of early life are 'stromatolites' - here's an NG article on them. Note: they would not be all that obvious to explorers or probes...they look essentially like rocks.

http://news.nationalgeographic.com/n...-microbes.html

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Stromatolites are great; there are living examples in Australia, seen here
http://en.wikipedia.org/wiki/Image:S...n_Sharkbay.jpg

I've seen fossil ones on the Orkney island of Mainland.
A planet with stromatolites would be a very exciting find from an astrobiology point of view- but a little disappointiing perhaps for tourists.

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What about viruses?When they evolved?

Larger viruses are almost certainly parasitic bacteria that became simpler and so must have evolved after the cells that support them. But it is possible that some viruses are decendants of simple free living creatures that could have preceeded the cells they now parasitize and so could be closely related to the first life on earth.

I'm just shooting from the hip here, but I would think the first viruses may have been one of the very early steps from "simple" replicating molecules to actual "life" as generally defined - they are not essentially much else, and their structure is very simple - genetic material and some proteins. They evolve (mutate) relatively quickly, too (which would be as good a strategy back then as it is now), and don't reallly have a metabolism. Their only "life" process seems replication, and to do that, all they essentially do is hijack another lifeform's genetic material/proteins.

Hmm. I wonder also, as they do seem to attack cells, if they perhaps MAY have evolved later (as you suggested) - perhaps FROM the early replicating molecules, once one-celled life got started and provided a (potentially more abundant/vulnerable) new "food" source)?

Also, there are a number of different types of viruses that use different variations of replication strategies. A quick idea could be that those that use mainly RNA-based strategies could be more direct descendents of more simple entities than those that use DNA-based strategies. They've likely also greatly co-evolved with their hosts, and it's possible (likely?) that the earlier forms no longer exist. Just guesses...

Maybe a worthwhile topic for an hour or two of checking out later tonight.

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Hmm. That's a sort of degenerative evolution, though. Not to be difficult, but I don't know that that would be likely. Since all viruses are essentially parasitic and require a host, I would guess they probably evolved at about the time the first one-celled life formed (perhaps Archaea?) and have co-evolved since to adapt to different forms of life. I'm guessing they likely formed from either the more complex replicating molecules that may have been around, or perhaps even were initially the result of some RNA transcription error during replication of some early cellular life...?

This is a fascinating topic, and I know just enough to be dangerous here, and perhaps not quite enough to be very constructive. Still, one learns best by thinking and screwing up, no? (provided you learn you DID screw up and accept it)

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Actually, it's not, it's a form of adaptive evolution; like all parasites, viruses got another lifeform to do something so that they didn't have to, then lost the ability themselves. They didn't necessarily co-evolve at the same time as bacteria, they could have started hijacking other cells at any point within the existence of unicellular life.

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Fossil record of viruses?

Alien life probably won't look like anything presented in this thread thus far.

Since life developed really, early on, as if life developed as soon as the earth could support it, which means life is common right? Or, gentlemen, coincidence.

Perhaps what we'd find in a primordial sea are rocks, water, geology, yet, sadly, no life.

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I wish it would be possible to expect to collect on a bet as to whether or not, given a planet with initial conditions suitable for life, and time for it to develop, would life develop? I would be the farm on "yes". Life is the result of chemistry, dependent upon the laws of physics and thermodynamics. It's not exactly a freak accident, in my view.

Life, I would suggest, would be fairly common, but rarer the more complex, and that largely due to time (and reasons related to time); mainly because a planet (and any life that is initiated on it) is extremely lucky to go very long periods without catastrophic events interrupting things. There's a very good chance that, had early reptilian/saurian life not been wiped out once, but twice, that an intelligence species of saurians would have evolved millions of years ago - they were fairly well on the road 70 million years ago. What if they had another 20 million or so to go? or 30? We're the result and an additional 65 million years of evolution - after 2 or 3 mass extinctions made it possible for our evolutionary ancestors to get some traction, and a slew of ice ages pushed them to 'earn' their survival.

I will grant that is IS accidental that any particular form of life manages to evolve very far, and I also think some environments impose inherent limits on the degree of complexity/variation possible to evolve within them (eg. the sub-ice seas of Europa) but again, given time and a dynamic (but not TOO dynamic) environment, chemistry and, later, evolution, will do its work.

That said, for the very same reasons, I think it is a very rare thing for a life form to evolve to the same degree we are (intelligence-wise PLUS being in an evironment where that intelligence can be put to use, say, to develop technology - check out the cetaceans of earth; likely as 'bright' and as self-aware as we are in many ways, but lacking any possibility of developing technology in their environment and, as a result, the depth of understanding of the world we have).

Anyway, I think we'll find plenty of life out there, when we can start looking in earnest, but unfortunately, it would likely be the heirs of our heirs who'd be able to collect on any wagers we may make now, and I somehow find that both unstatisfying and demotivating in terms of making any bets.

On a side note, I found a great picture of Titan I hadn't seen before - take a gander:

http://blogs.chron.com/sciguy/archiv...034_modest.jpg

Attached Images

PIA09034_modest.jpg (14.8 KB, 11 views)

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BTW, it WOULD be interesting to see how evolution deals with similar problems on different planets - I would expect there'd be some similarities, at least, but still, there is a LOT of room for variation in detail. I do agree, there's not way to really 'know' until we can 'see', but still, there are limits - and there are good reasons for the way life on this planet has turned out (and look at the huge variation even here!). That said, I bet there are also plenty of surprises out there, too.

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It happens all the time. Technically there is no such thing as degenerative evolution, there is only what works. If becoming simpler and less complex helps you reproduce then it will be selected for. Degenerative is a value concept we apply to it. We could also describe becoming simpler and less complex as elegant or efficient. Humans have lost body fur, a second stomach, the ability to synthesize vitamin C, oposable toes and so on, but we don't describe ourselves as the products of degenerate evolution even though in many ways we apper to have gone "backwards." (I put the word backwards in inverted commas because there is no direction in evolution, only what works. Fortunately for us, intelligence seems to work, or at least often enough to make it worthwhile.)

Some viruses definitely evolved from bacteria, but there is still a lot we don't know about viruses. What we do know is they are pretty much everywhere in vast numbers. (Don't panic!) It is quite likely that we have not yet discovered the simplest free living organisms on earth. If and when we find them they might be related to some of the viruses that we currently know, suggesting virus-like life evolved side by side with other cellular life, or preceeded it.

I understand your point and see the connection, but I don't think it's quite the same thing, really.


I'm not likely to panic about that. Really!

Speaking of simpler organisms - prions are a pretty interesting little buggers, too...! I don't think they are considered as 'free-living', though, but still - nasty things.


From what I can see and have read about it, and given the variety seen among different types of viruses, there's probably a bit of both there. It does seem 'obvious' that viruses evolved earlier than cellular life, and I would suspect many types did. Given the specific parasitic behavior between certain viruses and certain types of cells, co-evolution is also obvious in those cases.

I do find it pretty hard to accept that viruses "evolved" from bacteria, though not being an expert I can't rule that out - it just seems not only counter-intuitive (something I do try to watch out for before making/accepting assumptions based solely ON intuition), but it seems improbable from a logical point of view as well. As you seem to have some certain knowledge of that, I'll give you that and not argue it (and will look into on my own later).

It would seem to me, at first blush, that for that to happen, there'd need to be some pretty intense bacteria-bateria predation going on aimed at specific (types of) hosts that would induce significant evolutionary pressure towards a 'simpler is better' solution. Given that that's not an unlikely scenario back when bacteria were to top of the evolutionary ladder, I suppose that's possible (it could have happened even later (some forms of cellular a bacteria attacked perhaps became resistant, and the bacteria 'evolved' to a simpler form in response), but I think later there'd be too many other opportunities for 'forward' (increased complexity/robustess) evolution of bacteria to more complex forms, and co-evolution of viruses with bateria hosts would be an easier path for viruses to take, and some would likely follow that path as cellular and more complex life developed and evolved).

I am probably stepping WAY out of my depth here with this sort of speculation, but it IS an interesting topic. One wonders also if early viruses would be inherently more 'virulent' (more readily adaptable to more different (less specific) types of hosts), or would the opposite be the case? I suppose one could argue effectively either way. If the former, then I suppose that could pose a serious problem from possible infection from a primitive, relatively un-evolved extraterrestrial virus (assuming RNA/DNA genetics is not exclusive to earth, which seems at the very least "very possible").

the inquiring virus wants to know.......!

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"...wait for the ricochet."

I'm guessing that you aren't aware that there are parasitic bacteria that currently live inside other cells. Since they are protected from the environment by their host it should not be difficult for them to lose the characteristics that enable them to be free living, pretty much in the way blind cave fish lost their eyes as they weren't necessary anymore and a waste of energy.

There is an arms race between viruses and their hosts. The virus wants to get in and reproduce and the host wants to protect itself. But as for virulence is concerned, viruses don't want to make their hosts sick or kill them. They want their host to stay healthy and protect and spread the virus so a low key virus that can infect a cell but doesn't cause much damage can be the most sucessful. The most deadly viruses for humans are those that jump from another species or which don't rely on healthy hosts to spread themselves. These viruses may be mild in the animals they usually infect, but humans lack the original animal's defences and so the virus can reproduce wildly. Over time new strains of the virus that aren't so deadly to humans can develop. (The same principle applies to bacteria and other disease organisms.)