Oxford scientists say: Looks like no other intelligent life in whole universe (but keep looking)

[RJM Corbet]

The early atmosphere of the Earth would not support complex life, and in a few hundred million years it's unlikely to continue to do so. It's not a case of life being stuck as much as life can only evolve into the opportunities are available. Really, we live in a microbrial world and we complex forms are a temporary anomaly.

This is an interesting view. I think the origin of eukaryotic cell predates the great oxygenation event?

Anyway, see if you find this of interest:

Thank you. Those two guys rattle off like machine guns, lol

Sorry, I think I may have confused things here. IIRC the argument for the emergence of eukaryotes is that - in a chance and statistically impossible encounter - one type of microbe was coopted to live inside another as mitochondria and ended up providing energy enough for complex development ... suggests this process of microbes being coopted shouldn't be regarded in statistically impossible terms.

Late acquisition of mitochondria by a host with chimaeric prokaryotic ancestry
Mitochondria latecomers to the eukaryote cell

"The eukaryote cell is so much larger and more complex than the cells of bacteria and archaea that it is hard to recreate the steps whereby it evolved. One current view is that the evolution of eukaryotes was triggered when an archaea-like cell accommodated the bacteria that went on to become mitochondria.

An alternative view is that eukaryotes were well on the way to their modern form before they acquired the bacteria that became mitochondria. This second view is supported by a study by Alexandros Pittis and Toni Gabaldón showing that mitochondrial genes are more closely similar to those of their supposed bacterial relations than many other eukaryote genes are to their own inferred prokaryote cousins. This result, which challenges current views, suggests that mitochondria were late additions to a eukaryote cell that was already evolving."

Surely though, if eukaryotes came about by endosymbosis then cells, bacteria and everything else was probably swapping loads of bits and pieces, some being subsumed whole etc. So everything kinda had similar chemistry? In fact it wouldn't matter if there were large 'phase spaces' of incompatibility between different organisms. Evolution would select the ones that did work well together and these new organisms with new advantages would compete well for resources and crowd out the less able older cells, no? Especially as single cell organisms could reproduce very quickly and exponentially.

I don't know if it applies, but Lane puts it down to energy availability per gene:

“ … eukaryotes have up to 200 000 times more energy per gene than prokaryotes … a chasm that explains … why the bacteria and archaea never evolved into complex eukaryotes, and why we are never likely to meet an alien composed of bacterial cells … in an energy landscape where peaks are high energy and troughs are low energy, bacteria sit at the bottom of the deepest trough, in an energy chasm whose walls stretch high into the sky, utterly unscalable. No wonder prokaryotes remained there for eternity …

… for bacteria, bigger is not better. On the contrary giant bacteria have 200 000 times less energy per gene than a eukaryote of the same size. Scaling up a bacterium … runs into a problem with surface-area-to-volume ratio.

… Imagine scaling up the size of a city 625 fold, with new schools, hospitals, shops, recycling centres and so on; the local government responsible for all these amenities can hardly be run on the same shoestring ..."

(So there was no energy need for prokaryotes to 'evolve')

Enough from me. Out of my depth ...

 

[Stephen Palmer]

Those interested in the far-future possibilities of life on Earth would be interested in the excellent The Life & Death of Planet Earth by Peter Douglas Ward and Donald Brownlee. Here's my review of it.

 

[Wayne Mack]

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[Justin Swanton]

Those interested in the far-future possibilities of life on Earth would be interested in the excellent The Life & Death of Planet Earth by Peter Douglas Ward and Donald Brownlee. Here's my review of it.

My understanding is that half a billion years is about the limit life can survive on Earth, unless I'm missing something? I imagine a far future civilisation lingering at the tropical poles, a bit like the Homeworld humans on Karak.

 

[Stephen Palmer]

My understanding is that half a billion years is about the limit life can survive on Earth, unless I'm missing something? I imagine a far future civilisation lingering at the tropical poles, a bit like the Homeworld humans on Karak.

Yes, somewhere around that time scale, but it applies to multicellular life. Ward & Brownlee estimate 800 million years, but of course it's impossible to say. Bacterial and other forms of simple life will go on afterwards, but their time is limited by the average temperature of the planet, which, iirc, above about 50 degrees means only heat-loving Archaea can survive.
The time limit on animal life is also dependent on the amount of CO2 in the atmosphere. Once that is down to zero (via the Gaia positive/negative feedback processes) plant life collapses, which means most animal life will too because of food chains being founded essentially in plant life. CO2 levels reduce over long periods of time because the sun is slowly radiating more and more heat. Since life began on Earth, it's become 25% hotter. It was this realisation that helped James Lovelock develop the Gaia Theory.

 

[BAYLOR]

Yes, somewhere around that time scale, but it applies to multicellular life. Ward & Brownlee estimate 800 million years, but of course it's impossible to say. Bacterial and other forms of simple life will go on afterwards, but their time is limited by the average temperature of the planet, which, iirc, above about 50 degrees means only heat-loving Archaea can survive.
The time limit on animal life is also dependent on the amount of CO2 in the atmosphere. Once that is down to zero (via the Gaia positive/negative feedback processes) plant life collapses, which means most animal life will too because of food chains being founded essentially in plant life. CO2 levels reduce over long periods of time because the sun is slowly radiating more and more heat. Since life began on Earth, it's become 25% hotter. It was this realisation that helped James Lovelock develop the Gaia Theory.

In about a billion years , the sun will be 20 percent hotter and Planet Earth will become largely inhospitable to life and, projecting further down that road , could end up becoming a second Venus.

 

[Stephen Palmer]

Yes, that's about the size of it. Of course, evolution that far in the future could produce a few last surviving single-celled forms of life.

 

[BAYLOR]

Yes, that's about the size of it. Of course, evolution that far in the future could produce a few last surviving single-celled forms of life.

On can hope that long before that , man will have either long since left Earth for the stars or , will have found a way to move planet Earth away form the the sun and thus buy it more time.

 

[paranoid marvin]

On can hope that long before that , man will have either long since left Earth for the stars or , will have found a way to move planet Earth away form the the sun and thus buy it more time.

If we haven't , then there is no way we will survive that long. Since the advent of the atomic weapons, we have barely survived the last half century.

 

[paranoid marvin]

If we haven't , then there is no way we will survive that long. Since the advent of the atomic weapons, we have barely survived the last half century.

Which probably sounds more negative than I meant! But for lots of different reasons, whether it be a natural disaster from space or from Earth , a man-made act or simply the exhaustion of resources, we only have a pretty limited time to branch out from our planet. Couple of thousand years perhaps but certainly not much more than that. Which should still be ample time to do something about it. There's no reason why within the next couple of hundred years that we can't have settlements on the Moon.

 

[K. Riehl]

Most of these theories presume life developing the way it did on Earth

What if it Silicon based? Possibility of Silicon-Based Life Grows - Astrobiology Magazine

What if the building blocks of life can develop in space? https://economictimes.indiatimes.co...locks-of-life-found-in-comet-by-nasa-research

What if the center of the galaxy has a greater chance at development of life due to higher cosmic ray effects? How cosmic rays may have shaped life

What if life develops on Radiation as a source of energy ? Could Life Thrive on Radiation? Scientists Say It’s Possible

Last but not least, we have only developed Radar, Radio and Radio Telescopes, Laser and fiber optics in the last 100 years. Why couldn't we develop or discover something new in the areas of communication in the next 200 years? Yes, I am an optimist.

 

[Vertigo]

Most of these theories presume life developing the way it did on Earth

What if it Silicon based? Possibility of Silicon-Based Life Grows - Astrobiology Magazine

What if the building blocks of life can develop in space? https://economictimes.indiatimes.co...locks-of-life-found-in-comet-by-nasa-research

What if the center of the galaxy has a greater chance at development of life due to higher cosmic ray effects? How cosmic rays may have shaped life

What if life develops on Radiation as a source of energy ? Could Life Thrive on Radiation? Scientists Say It’s Possible

Last but not least, we have only developed Radar, Radio and Radio Telescopes, Laser and fiber optics in the last 100 years. Why couldn't we develop or discover something new in the areas of communication in the next 200 years? Yes, I am an optimist.

Silicon based life implies using silicon instead of carbon to form the long chain molecules. This paper has only shown that we can force silicon to be incorporated in carbon based molecules not replace the carbon in them. "scientists have for the first time shown that nature can evolve to incorporate silicon into carbon-based molecules" and "This does not prove that silicon- or organosilicon-based life is possible, but shows that life could be persuaded to incorporate silicon into its basic components. " Now that shows that it is theoretically possible but it is, I believe, going to be far less efficient or flexible and, combined with the fact that carbon is far more abundant in the universe (nearly 8 times more common than silicon, I believe), it seems highly unlikely, though I'll concede not impossible, for silicon based life to out compete carbon based life.

We have long known that the "building blocks of life" or organic compounds can form in space. However there is a vast gulf between those building blocks forming and life itself forming. If you have some carbon and oxygen it does not automatically follow that you have a fire just the potential for it in the right conditions.

Mutation is essential to evolution and no doubt cosmic rays have had some impact on those mutations but there must also be some stability. If everything is mutating constantly then stable life is going to be highly unlikely. I would still contend that excessive mutation is likely to be the case closer to the galactic centre. Some mutation is good, too much mutation is bad.

Ultimately anything is possible but when dealing with something that evolves randomly over millions of years you need to look at what is most likely to happen. Whatever that is it is likely to dominate.

We have pretty much all of the components mentioned available right here within the solar system and yet, so far, have found no evidence of any other life than our own within the solar system. That's not to say it isn't out there but the longer we keep looking and not finding it the less likely it is. If I was arriving in the solar system for the first time it would be incredibly easy to spot the life on Earth it is incredibly obvious but if there is any other life then it is so hard to spot it must be far less abundant, with the possible exception of life in the atmospheres of the gas giants. That might be hard to spot and yet be very abundant. I have never denied that other life might exist but the more elusive it appears to be the less likely it is to be.

 

[RJM Corbet]

What if it Silicon based? Possibility of Silicon-Based Life Grows - Astrobiology Magazine

It comes round again to the fact that the origination of carbon based life was not a simple or definite thing. Assuming carbon life is the 'easiest' form of life, the difficulties for silicon based life originating are multiplied. Which does not mean impossible. Perhaps some sorts of silicon based bacteria things do exist out there somewhere, but the chance of them ever progressing to become more complex is also greatly reduced.

What if the building blocks of life can develop in space? https://economictimes.indiatimes.co...locks-of-life-found-in-comet-by-nasa-research

This is acknowledged. The difficult part is the process of the building blocks combining in exactly the right way to become animated. Again, not impossible. But assuming that life was never the GOAL of the universe, there is no way of assuming that, because the blocks exist, they will assemble themselves?

What if the center of the galaxy has a greater chance at development of life due to higher cosmic ray effects? How cosmic rays may have shaped life

What if life develops on Radiation as a source of energy ? Could Life Thrive on Radiation? Scientists Say It’s Possible

Cosmic rays may have been part of the combination that enabled abiogenesis of life on Earth. If so, they could obviously also be a part of abiogenesis elsewhere? Of course, once life has come into being, all bets are off. Life is amazingly resilient and inventive.

EDIT
Post landed at the same time with @Vertigo's

 

[paranoid marvin]

Silicon based life implies using silicon instead of carbon to form the long chain molecules. This paper has only shown that we can force silicon to be incorporated in carbon based molecules not replace the carbon in them. "scientists have for the first time shown that nature can evolve to incorporate silicon into carbon-based molecules" and "This does not prove that silicon- or organosilicon-based life is possible, but shows that life could be persuaded to incorporate silicon into its basic components. " Now that shows that it is theoretically possible but it is, I believe, going to be far less efficient or flexible and, combined with the fact that carbon is far more abundant in the universe (nearly 8 times more common than silicon, I believe), it seems highly unlikely, though I'll concede not impossible, for silicon based life to out compete carbon based life.

We have long known that the "building blocks of life" or organic compounds can form in space. However there is a vast gulf between those building blocks forming and life itself forming. If you have some carbon and oxygen it does not automatically follow that you have a fire just the potential for it in the right conditions.

Mutation is essential to evolution and no doubt cosmic rays have had some impact on those mutations but there must also be some stability. If everything is mutating constantly then stable life is going to be highly unlikely. I would still contend that excessive mutation is likely to be the case closer to the galactic centre. Some mutation is good, too much mutation is bad.

Ultimately anything is possible but when dealing with something that evolves randomly over millions of years you need to look at what is most likely to happen. Whatever that is it is likely to dominate.

We have pretty much all of the components mentioned available right here within the solar system and yet, so far, have found no evidence of any other life than our own within the solar system. That's not to say it isn't out there but the longer we keep looking and not finding it the less likely it is. If I was arriving in the solar system for the first time it would be incredibly easy to spot the life on Earth it is incredibly obvious but if there is any other life then it is so hard to spot it must be far less abundant, with the possible exception of life in the atmospheres of the gas giants. That might be hard to spot and yet be very abundant. I have never denied that other life might exist but the more elusive it appears to be the less likely it is to be.

Yes it would be almost impossible NOT to notice life on Earth, and as you say any life within our own solar system becomes more remote by the day. It was less than a century ago when people really thought that there could be canals on Mars or tropical rainforests on Venus, and that was with more than 1000 years of knowledge and quite sophisticated equipment.

Given the likelihood of water on certain moons in our solar system, it would surprise me if we didn't find some organisms of life there. Regardless of other factors, I feel that the presence of water is one of the key factors of life. And if there is water in several places in our solar system, we can only assume that it is likely to be abundant thoughout the universe. But what we know changes, and in the next 100 years it is entirely possible that much of what we know is true for Earth maybe entirely different for other places out there.

 

[Vertigo]

Sir Patrick Moore was a great believer of life on Mars right up until the first landing or at least the first orbital images, I think.

I agree that it is more than possible there might be microbial life where liquid water is present on some of the moons in the solar system. Although water is not the only prerequisite. And it is highly likely that water is in abundance throughout the universe since hydrogen and oxygen (and carbon) are two (three) of the most commonly found elements. I think the most common four elements are hydrogen, helium, oxygen and carbon.

 

[paranoid marvin]

It comes round again to the fact that the origination of carbon based life was not a simple or definite thing. Assuming carbon life is the 'easiest' form of life, the difficulties for silicon based life originating are multiplied. Which does not mean impossible. Perhaps some sorts of silicon based bacteria things do exist out there somewhere, but the chance of them ever progressing to become more complex is also greatly reduced.

This is acknowledged. The difficult part is the process of the building blocks combining in exactly the right way to become animated. Again, not impossible. But assuming that life was never the GOAL of the universe, there is no way of assuming that, because the blocks exist, they will assemble themselves?

Cosmic rays may have been part of the combination that enabled abiogenesis of life on Earth. If so, they could obviously also be a part of abiogenesis elsewhere? Of course, once life has come into being, all bets are off. Life is amazingly resilient and inventive.

EDIT
Post landed at the same time with @Vertigo's

Yes, once something has been proven as not impossible - as we ourselves are evidence - it all comes down to the chance of it happening again.

We have seen on Earth how technically beautiful and inventive nature can be. We have seen in space how beautiful and varied is the night sky. In a Universe teeming with stars and planets, moons and comets, quasars and blackholes, dark matter and antimatter and all manner of other things yet to be discovered, it would be a shame if only the inhabitants of one insignificant little planet in a far corner of the galaxy could have any appreciation for the aesthetics of it all.

 

[Vertigo]

Yes, once something has been proven as not impossible - as we ourselves are evidence - it all comes down to the chance of it happening again.

We have seen on Earth how technically beautiful and inventive nature can be. We have seen in space how beautiful and varied is the night sky. In a Universe teeming with stars and planets, moons and comets, quasars and blackholes, dark matter and antimatter and all manner of other things yet to be discovered, it would be a shame if only the inhabitants of one insignificant little planet in a far corner of the galaxy could have any appreciation for the aesthetics of it all.

It would indeed be a shame, but that's one of the things that worries me. I wonder how much of the speculation on other life, or at least other intelligent/technological life is just wishful thinking, combined with showing that something is possible and then extrapolating that in such a vast universe it is therefore inevitable.

 

[paranoid marvin]

It would indeed be a shame, but that's one of the things that worries me. I wonder how much of the speculation on other life, or at least other intelligent/technological life is just wishful thinking, combined with showing that something is possible and then extrapolating that in such a vast universe it is therefore inevitable.

I agree, but - for want of a better word - nature largely does things that make sense and it also seems to promote and support life. If the nature of the universe is seen in microcosm on Earth then we are truly not alone. I find it hard to accept that the rest of the universe is filled with dead balls of rock and gas, but as you say part of that is down to be wishing it not to be so.

 

[K. Riehl]

This is all true, as far as we understand how life developed here on Earth. Maybe conditions at center of the galaxy are so radically different that life found a different way to develop. Maybe they exist on radiation and consider the cold outer regions of the galaxy as unable to have developed life because there isn't enough radiation to maintain life as they know it.

We use spectroscopy to figure out things about suns but we have almost zero information about planets. Maybe the next couple of improvements in technology will allow us to directly observe planets and then we will know but until then we really don't know.

How can we make universal assumptions based on the sample size of one solar system? If we lived in Antarctica and had no knowledge of the rest of the Earth wouldn't we believe that life was rare and subzero temperatures were normal. How would we imagine the jungles on the equator?

The universe is vast and over a time period of billions of years even the rare event such as the spark of life may have happened millions of times.

I still prefer to be optimistic about life elsewhere. The tipping point will be when we can directly observe plants existing in the Goldilocks zone. Then my hopes can crushed or thrilled with the discovery.

 

[paranoid marvin]

This is all true, as far as we understand how life developed here on Earth. Maybe conditions at center of the galaxy are so radically different that life found a different way to develop. Maybe they exist on radiation and consider the cold outer regions of the galaxy as unable to have developed life because there isn't enough radiation to maintain life as they know it.

We use spectroscopy to figure out things about suns but we have almost zero information about planets. Maybe the next couple of improvements in technology will allow us to directly observe planets and then we will know but until then we really don't know.

How can we make universal assumptions based on the sample size of one solar system? If we lived in Antarctica and had no knowledge of the rest of the Earth wouldn't we believe that life was rare and subzero temperatures were normal. How would we imagine the jungles on the equator?

The universe is vast and over a time period of billions of years even the rare event such as the spark of life may have happened millions of times.

I still prefer to be optimistic about life elsewhere. The tipping point will be when we can directly observe plants existing in the Goldilocks zone. Then my hopes can crushed or thrilled with the discovery.

Some good points. What we know is all based on how things are here on Earth; that is the only basis we have. What we know to be undoubtable fact as changed over time, dependant on the progress of science. Who is to say (similar to what Douglas Adams suggested) that there aren't microscopic worlds out there inhabited by intelligent civilisations that could exist on the head of a pin? Which on the face of it, in intergalactic terms is what the size of our world is in comparison to the size of the universe (or perhaps even multiverse).

I understand that oxygen was originally poisonous to humans, but over time we adapted to the extent that we now absolutely rely upon it. Who is to say that extreme heat or cold or radioactivity is conducive to life in other parts of the universe, and that those looking from afar at our world would see the oxygen-filled atmosphere as making life impossible on our planet, just as we see the atmosphere of Venus making life impossible.