[X] My Assistant

[Guest_Richard Trigaux_*]

I don't know if what you speak about can be really "photosynthesis". We can speak of photisynthesis when light is used. (Be it visible, IR, UV, etc).

H2S is not very abundant on Earth. It exists only on special places (volcanoes, and only recently into decaying organic matter) and it quickly transforms itself into sulphuric acid, from the simple presence of water. So we can imagine that an H2S life exists only in small quantities, into small niches, and thus has little opportunities to evolve. Of that this situation exerted a strong evolutionary pressure toward other solutions, like light use.

One important thing into the probability of an evolutionary step to happen, must be the volume of present life: more volume, more probability of a mutation. Like in the simplified tumor growth model: a given mutation becomes statistically mandatory when the tumour reaches a certain volume. On a planet where there are a small number of evironments, and of small dimentions, evolution must be slower.

On earth, until the precambrian radiation, life existed only into the oceans. And the only places into the oceans where there are voluminous and numerous ecology niches is around the coasts. On Earth, continents began to form maybe 3.5 billions years ago (the oldest rocks) and increased at about a constant rate since. So perhaps the evolution pace accelerated only when there was enough continents providing many coast lines. On A 100% ocean planet, evolution would be very slow. It would be optimum with a majority of continents, provided that the remainding seas still communicate together. That makes about 60-70% of continents.


About H2S based life, I heard once a story in Romania, where there was a series of closed caves with strong emanations of H2S (communicating through water filled galeries). Here existed a whole ecosystem of bacteria eating H2S and absorbing its energy, together with a series of worms and bugs which formed a complete food chain. All this living in the dark and the pong, passing their time to eat each other, perhaps it was hell under Earth...

[Thorsten]

Salut Richard.

The energy generation of green sulphur bacteria is photosynthesis in its strictest sense. (Technobabble start: It contains bacteriochlorophyll, which is excited by the absorption of visible light and produces the electron gradient necessary to generate chemical energy, Technobabble end). It’s just not “powerful enough” to “split water” (this evolutionary breakthrough came later - with cyanobacteria and plants)). Of course, these bacteria need places where H2S as photosynthetic electron donor is obtainable; therefore – as you mentioned - a strong evolutionary pressure towards more easily available electron donors such as water existed.

Coming back to your question, why multicellular complex life emerged long after oxygen-producing photosynthesis was established. Indeed, organisms capable of responding to light (earliest photosynthesis) were found as early as 3,5 billion years ago (Warrawoona, Australia), only a few 100 million years after the end of the heavy bombardment phase. Stanley Miller estimated in the 1990s that some very primitive bacteria could have evolved in not more than a few tens of millions years out of prebiotic soup (which is heartening, when you think of the possibility of life in places like Enceladus).
Why then did it take so long for complex life to emerge?

I agree that the existence of continents might have played an important role – even today, the majority of marine species live in shallow-water regions close to the coasts, while the biological diversity in the deep sea is much lower. And since all ocean life is dependent on nutrients, which mostly come from the land as runoff from rivers and streams, the growth of the continents might have influenced evolution. Unfortunately, the growth of continents is the direct results of plate tectonics, which has proposed to be a key factor for life on Earth (including its function as global thermostat via the CO2-weathering cycle and its possible role for the generation of the Earth’ magnetic field). So, I guess, it’s kind of difficult to separate one from the other.

However, I believe that there is another important factor. Look at the enormous complexity of even the simplest modern day bacteria, the perfection of DNA damage repair after UV radiation or the precision of how genetic information is transcribed to proteins and passed on to the next generation. Without this elaborate machinery complex life would have never been possible. Take for example an especially sophisticated high fidelity nanomachine – the DNA polymerase (which copies the genetic information when the cell divides to become two cells). This nanomachine copies genetic information as fast as 1kb/ sec, and has an error rate of 1 bit/ 10e9 bits). A higher mutation rate would be deleterious for any organism, while a lower mutation rate would probably be unbearably expensive and very slow (since the proofreading of the nanomachine consumes a lot of chemical energy). Interestingly, it has been assumed that this protein directly affects the complexity of all life on Earth. DNA polymerase makes around 3 mistakes each time a human cell divides, which allows all humans to pass accurate genetic instruction from one generation to the next, and also to minimize the chance of harmful changes in somatic cells that would lead to cancer.
However, although the mutation frequency in complex life forms is low, it is nevertheless thought that the limit of the number of essential proteins that any organism can encode is 60’000 (humans have 30’000). If the mutation frequency was for example ten times higher this would have limited an organism to about 6000 essential genes. In that case evolution would have probably stopped at an organism less complex than a fly.

In summary, the generation of a simple reproducing system is probably easy, but the incredible perfection of complex life might have taken a long time.

Thorsten

[Guest_Richard Trigaux_*]

Thanks for your very interesting reflexions, Thorsten.


Until recently, what I was thinking is that what took many time for evolution, from very early bacteria to multi-cellular organism, was precisely the capacity to encode, not only the infos for the cell itself, but also for the body organization. This capacity appeared slowly, first with the capacity for cells to exchange chemical messages and undertake specific chemical activities accordingly. Then appeared the capacity for cells to move relative to each other, stick together, etc. What produced the pre-cambrian explosion of life forms was probably the capacity of having the organism form itself coded into DNA, with the series of gens known as homeobox, which work with an hormonal gradient (from head to tail) and reacts after the various concentrations to form the various body segments. There was an early evolution testing many kinds of symmetries, until the bilateralians won (this was already discussed before in this thread).

The appearance of multicellularism produced a huge increase in genome size, and further the appearance of complex organs produced another order of magnitude in genome size. Think for instance that simply the smelling sense counts for 10% of the rat genome, as each smell has to be recognized by a special molecule. The complex brain circuitry too consumes a lot of genentic resources.

So, as you noted, this can work only with an efficient nanomachine like the DNA transcribers (I could not imagine they were so fast). It is clear that poorly performing nanomachines would severely limit the complexity of living being (and, as you note, we humans are about at 50% of the limit, and we must pay the cost in terms of cancers and genetic diseases).

The questions are, if we want to explain all this in a multi-path chain of events, which was the order of events, their overal probability?

-Was the appearance of efficient nanomachines the cause of complexification of life, or did this complexification appeared much later, arising slowly from difficult problems to solve? Or did simply the efficiency of the nanomachines increased steadily to cope with the complexity of their task?

-Complexification and multi-cellularism appeared simultaneously in plants and animals, when it seems that their lineage separated much sooner. But I am not sure of this: what is the exact evolution tree for ancient plants (stromatholites, cyanobacteria), modern green plants, animals? Could only a relatively recent single event before the precambrian explosion of life (like the appearance of an efficient nanomachine) have triggered all what we see today? Or had we really two independent evolution paths (animals and plants) which had to solve the same problems (nanomachines, complexity, multicellularism) and solved them in about the same time? This later question is especially interesting in an astrobiology scope, as animals and plants had separated genetic evolutions, as if they were on two different planets.

The vision I defend in this thread of a series of random steps (the duration of each step being the inverse proportion of its probability) gets more complicated, as passing each step depends of many "small" events. This makes a more continuous flow of events, but this flow can still be fast or slow according to the difficulties it has to solve.

[ljk4-1]

Methane-belching Bugs Inspire A New Theory Of The Origin Of Life On Earth

http://www.science.psu.edu/alert/Ferry5-2006.htm

12 May 2006 --Two laboratories at Penn State set out to show how an obscure undersea microbe metabolizes carbon monoxide into methane and vinegar. What they found was not merely a previously unknown biochemical process--their discovery also became the inspiration for a fundamental new theory of the origin of life on Earth, reconciling a long-contentious pair of prevailing theories.

This new, "thermodynamic" theory of evolution improves upon both previous theories by proposing a central role for energy conservation during early evolution, based on a simple three-step biochemical mechanism.

[ljk4-1]

This paper sounds rather relevant to the most recent discussion here:

Evolution of Photosynthesis and Biospheric Oxygenation Contingent Upon Nitrogen Fixation?

Journal-ref: International Journal of Astrobiology, vol. 4 (3 & 4): 251-257, Oct. 2005

http://arxiv.org/abs/astro-ph/0605310

[Guest_Richard Trigaux_*]

Thanks ljk4-1 for once again posting interesting references.


To summarize the quoted article, the appearance of modern and efficient photosynthesis, not only depends of the ability to decompose water itself, but also to the ability to fix nitrogen (to form proteins, as in modern agriculture). Only a set of several conditions allowed efficient photosynthesis (they say between 0.5 to 2.5 billions yeras ago) despites the fact that photosynthesis existed since much more time (stromatholites, 3 billions years or more).

So, between the appearance of the first bacteria (likely between 4 or 4.5 billions years ago) and the appearance of evolved life (multicellular + efficient photosynthesis + oxygen + brains) 0.6 to 0.8 billions years ago, there was a long and slow process where several important and independent steps had to be overcome without help from each other:
-efficient photosynthesis
-nitrogen fixation
-exhausting oxygen sinks (iron, etc)
-homeobox gens system
-etc

And this process took roughly 3 billions years, during wich life on Earth was limited in protected places and played only little geochemical role.

So we can hypothetise, as many insisted in previous posts, that the gathering of so many independent conditions, could explain that evolved life appears only after billions years, in such a way that we could be really among the firsts. And on many planets, the life conditions would become unfavourable before evolved life appeared.

Once again we have an explanation of the Fermi paradox, as some pages ago with the story of the gamma ray bursts able to sterilize a galaxy. But they showed much less dangerous, and only into ancient galaxies. So nothing is sure yet. We have to wait to be able to look at the spectra of many Earth-like planets and look for evidence of photosynthesis.

[ljk4-1]

Once again we have an explanation of the Fermi paradox, as some pages ago with the story of the gamma ray bursts able to sterilize a galaxy. But they showed much less dangerous, and only into ancient galaxies. So nothing is sure yet. We have to wait to be able to look at the spectra of many Earth-like planets and look for evidence of photosynthesis.

Speaking of the Fermi Paradox:

The Fermi Paradox in the light of the Inflationary and Brane World Cosmologies

Authors: Beatriz Gato-Rivera

Comments: Chapter of the book `Trends in General Relativity and Quantum Cosmology', Nova Science Eds, New York, 2006, with several minor improvements

The Fermi Paradox is discussed in the light of the inflationary and brane world cosmologies. We conclude that some brane world cosmologies may be of relevance for the problem of civilizations spreading across our galaxy, strengthening the Fermi Paradox, but not the inflationary cosmologies, as has been proposed.

http://arxiv.org/abs/physics/0605096

[Bill Thompson]

From my personal experience I can conclude that there are politics in this science.

I think that if a scientist or engineer looks at all the available information and concludes that it might be more likely that there are currently no creatures in the galaxy like us, he is probably going to be quiet. This would be and is an unpopular view. It is unpopular not because it is wrong. It is unpopular because it is not as exciting.

I wonder if anyone would agree with me.

Then again, I might be all wrong and I need to go back and study some more and different information. I will have some free time in June. I will make use of my vacation.

[ljk4-1]

From my personal experience I can conclude that there are politics in this science.

I think that if a scientist or engineer looks at all the available information and concludes that it might be more likely that there are currently no creatures in the galaxy like us, he is probably going to be quiet. This would be and is an unpopular view. It is unpopular not because it is wrong. It is unpopular because it is not as exciting.

I wonder if anyone would agree with me.

Then again, I might be all wrong and I need to go back and study some more and different information. I will have some free time in June. I will make use of my vacation.

For most of science's history, practitioners were often made or made to feel
silent about supporting the concept of extraterrestrial life, not the other way
around.

People like Lowell were the exception, but he wasn't a Ph.D. scientist, and
when it was finally learned that the canals of Mars were just optical illusions
and no great, ancient, dying Martian civilization existed, mainstream
astronomers shoved most of the ideas of life elsewhere beyond the
back burner. The problem was that all aspects of the alien life idea
got put back along with Lowell.

Only recently has it become generally "acceptable" to talk about and support
an idea which as far as I and others are concerned should be one of the most
important topics and quests in human history. But even then, the prejudices
and lack of knowledge by much of the public and even conservative scientists
still make the subject one of derision and don't take it seriously. A subject that
has been given mostly lip service and spent most of its devoted time in sporadic
searches with limited resources over a few decades. Oh yes, and two immobile
landers on a planet with a surface area equivalent to Earth scratching at the dirt
and causing more confusion than results. And that was thirty years ago.

And have you seen some of the books that have come out in the popular press
in the last few years? Stephen Webb's If the Universe is Teeming with Aliens...
Where is Everybody?, Ward and Brownlee's Rare Earth series, The Privileged
Planet by Gonzales and Richards, and the recent Civilized Life in the Universe
by Basalla - they all contend that maybe the Cosmos has simple lifeforms, but
complex life? Nah, we're probably it.

I sense something more than just the claim that our lack of evidence for ET life
means there is none elsewhere, especially in the case of Gonzales and Richards,
the latter of whom is a theologian.

The arrogance and narrow-mindedness of a species that just started to understand
its existence beyond the mythologies and has barely left its home planet, yet because
the Universe it lives in hasn't bothered to make its other likely intelligences known
has concluded that there aren't any. Are we still reeling from the shock of the fact
that we are less than flyspecks in a wider Cosmos so we have to "attack" the one
major unproven aspect of this reality, that of other intelligences? Are we actually
afraid of "competition" like some primitive animal defending its perceived territory?

We need to search, pure and simple. What has happened to scientific curiousity,
exploration, and boldness? We risk stagnation and worse if we just accept our
prejudices and close our minds to seeking the truth.

[djellison]

What happened to scientific curiosity, exploration and boldness?

Easy...

Their budget got cut.

Ask Joe Public if he wants to spend vast swathes of money looking through a haystack for a needle that we may or may not be able to detect and which may or may not even exist - and he'll say no - it's a waste of money - and you have to admit, it's a perfectly valid point of view.

The finding of life in this solar system is clearly an important goal within space agencies across the world - but it costs an enormous ammount of money so it has to be done frustratingly slowly.

Finding life elsewhere - imho SETI is going to come up blank however long you try. The maths just doesnt add up as far as I'm concerned. The haystack too large, the needle too small, our eyes not powerfull enough.

However - programs such as TPF, Lisa etc - programs dedicated to finding the sorts of bodies around the sorts of stars at which would be familiar to us - again, are interesting and worthwhile exercises. Let's search in a sensible way - lets get that first spectra of an earth like body around a sun like star and find what's going on. Carefully, systematically, intelligently looking for interesting things 'out there'.

But at the end of the day - go and say to 1000 members of the general public "We need to search, pure and simple" - they're going to ask why...what good would it do them? And they have a point, they really do.

SETI may be a bold and important and honourable thing to some, but to many it's just pointless nonsense.

Doug

[ljk4-1]

But neither you nor Joe Public have to extract any of the tiny fraction
of your income taxes that once went to NASA's brief flirtation with SETI in
the early 1990s for the projects running now (and being British, you never
had to pay any amount for SETI). And they are all still much less
expensive than your average space probe.

I could equally make a case that Joe Public does not understand,
appreciate, or support sending vehicles to other worlds. After all,
they're just a bunch of rocks and ice in space, right? What could
we do with those? And shouldn't the money be better spent to
alleviate the problems right here on Earth?

Don't you just love that last phrase. Billions spent every year on
poverty, pollution, crime, etc., but they seem to still be here. Ah
well, we still shouldn't be sending rockets to Mars, anyway.

As for SETI being foolish and pointless, in addition to the already
mentioned inexpensiveness of the endeavor (which once again I
will state is not related to space probes and NASA has now shown
how little they really support even astrobiology), I wonder how the
various real scientists, engineers, and investors who have supported
SETI over the years would response to such labels? If you ever look
at who is in the SETI field, you won't find many crackpots and others
of the type associated with UFOs et al.

I have never thought that SETI would be easy or brief. I am thinking
of the long term investment for humanity and science. Since it is not
impossible that someone might be trying to signal us, or that we might
pick up a stray transmission, spending a few bucks on a few telescopes
to watch the skies isn't a crime or a waste of time, at least to those who
do this type of activity. Just because it isn't in "vogue" with some doesn't
make it less viable. Science isn't (or shouldn't be) a fashion trend.

To me the real crime is that there may be ETI out there trying to make contact
or at least broadcasting, and we miss it. That will probably make the nay-
sayers and religious types happy, though. We wouldn't want to learn
anything new from a different perspective.

I guess this is what happens when one has grown up in a more optimistic
age and am now living in a more conservative and inward-looking one.

The final point: Space probes, SETI - they are all about exploring the
Universe and improving our understanding of it. Joe Public usually does
not make a differentiation between the two. Since our goals have many
similarities, it is a shame to have to be at odds when both fields are
exploring space (and I happen to support both very much).

[Bob Shaw]

'Joe Public' probably has a better take on SETI than the academics do - it's simple to understand as a concept, and culturally most people are prepared to accept that other intelligent life exists (although often in a Star Fleet uniform!). If you then go on to explain how cheap most forms of SETI are, then questions start getting asked about expensive science...

...and if any formal test of public support for SETI is required, then just look at the SETI at home phenomenon - 'Joe Public' got involved just because it was a cool thing to do...

Bob Shaw

[djellison]

The final point: Space probes, SETI - they are all about exploring the
Universe and improving our understanding of it.

Seti has nothing more to do with exploring the universe than looking at a photo of Everest has to do with climbing it. I'd rather we made a systematic survey for habitable exoplanets than just sat waiting for the phone to ring.

We have no data with which to make a judgement as to if it's fundamentally futile, or destined for rapid success. I'd rather we did the science to fill in more of the blanks of Drakes equation rather than just assumed there was something valid at the end of it.

Being a member of TPS, I pay for Seti as it happens, and do not begrudge it at all, nor Optical Seti - because there's every chance that spinoff science may occur in both cases that has nothing to do with SETI whatsoever - for example Seti@Home spawned a plethora of similar systems for medical research, and indeed Stardust@Home. Optical Seti has produced some excellent new chip technology and the data that it generates could offer some interesting studys into variable stars and so on.

It's simply a case of opinion - you're clearly very pro Seti - I'm not. Nothing wrong with that.

Doug

[ljk4-1]

I have long had this bad habit of assuming that those who are into the
subjects I like - in particular, astronomy and space exploration - are into
all aspects of the field. But reality jars me loose from that preconception
often enough.

Perhaps it all began back when I was young (cue sad violin music), where
I grew up in an isolated town where no one I knew was into space, particularly
like I was. And aliens - might as well just be accused of being a witch, even
after the first Star Wars film came out.

Back then, I was thrilled when I found anyone who liked any aspect of my
interest, even if they only watched Star Trek. I naively assumed that if they
were into Star Trek, they must also be into space and astronomy (cue slowly
rising sad violin music, with a little piano thrown in). But sadly, I learned
that while they thought Mr. Spock and phasers blowing up starships were
really cool, most of these same people couldn't have cared less about real
space probes going to Mars or starships or SETI or the Sun as viewed with
a hydrogen alpha demulsifier.

So I grew up, moved away to the big city for my first real job, and discovered
that even though there were actual people who liked space and astronomy,
they still looked down on SETI. Maybe it was because it isn't something
that provides instant gratification. Maybe they saw Aliens one too many
times. Maybe they were abducted. Who knows?

But... I understand now. Everyone likes their own thing, and just because
it has something to do with space does not mean they are into it or accept
it. I understand now.

So, go on... go on with your deep space probes to alien worlds with your
instant gratification and the really cool photos of craters and geysers and
rocks. I'll be alright, really. I'll be the one just quietly sitting up on some
grassy hill on a cool evening, looking up at the stars... and wondering.

And while I'm up on that hill, I'll also be looking at my 8x10 glossy photos
of the Himalayas I always carry around with me, because, some day, I'm
gonna climb those mountains. I swear.

Cue crescendo music. Fade to black.

For Carl.

[Guest_BruceMoomaw_*]

Okay, but when they land on that hill one night, carry you off and start sticking that long pointed thing into you, don't say I didn't warn you...

Actually, I've always had a gigantic soft spot for SETI. It seems to me that, where space-related research is concerned, its ratio of cost to potential benefit is almost unmatchable, and the stupefying scientific ignorance shown by the Congressmen who keep slapping it down (most of them Democrats, alas) is simply infuriating. Given that the program could be more than adequately funded for just a few tens of millions of dollars out of NASA's annual budget, this is one space project I definitely feel the government should get back into. (To quote Woody Allen: "It should be kept in mind that when scientists talk about 'life in outer space' they are frequently only referring to amino acids, which are never very gregarious, even at parties.")