“With exoplanets we are entering new territory,” says René Heller (Leibniz Institute for Astrophysics, Potsdam), talking about recent studies looking at axial tilt as a parameter for habitability on a planet. Heller is getting at the fact that while we’ve studied the axis of a planet’s spin relative to the plane of its orbit rather thoroughly here in our own Solar System, we are a long way from being able to discern the axial tilt of exoplanets, much less make definitive statements about its effect on habitability. Right now we can say something about the size, mass and orbital period of many distant planets (and in a few cases, some of the components of their atmosphere) and that’s about where our knowledge stops.
Heller imagines the Earth with an axial tilt something akin to that of Uranus, whose equator and ring system run almost perpendicular to the plane of its orbit. Introduce such high obliquity to the Earth and the north pole would point at the Sun for a quarter of the year and in the opposite direction for another three months. As the year progresses, one pole is scorched while the other freezes, and then the situation reverses. As Heller told Astrobiology Magazine in a recent story, “The hemispheres are cyclically sterilized, either by too strong irradiation or by freezing.”
In the same article, George Williams (University of Adelaide) speculates that an axial tilt of as little as 40 degrees would provide a tough environment for complex animals because of the exceedingly hot summers and cold winters that would prevail over much of the globe. He points to evidence for high obliquity in the early Earth, arguing that it may have been a change in axial tilt to something closer to today’s 23.5 degree obliquity that prompted the explosion of lifeforms in the Cambrian era some 540 million years ago. Glacier studies may be giving us some evidence for high obliquity throughout much of Earth’s early history, though what would have altered our planet’s tilt roughly 550 to 600 million years ago to make all this happen remains a mystery.
Plants on the Early Earth
Exoplanets raise so many questions about our own planet’s past, and the obliquity issue is but one factor in all this. We can also home in on the question of plant life, examined in a recent Scientific American blog entry with the assertive title Thanks to Plants, We Will Never Find a Planet Like Earth. The story looks at an open question — how was the surface of the early Earth shaped, particularly by the waters that weathered bare rock to create the soil plants needed to thrive? Martin Gibling (Dalhousie University, Nova Scotia) and Neil Davies (University of Ghent) have analyzed sediment deposition back hundreds of millions of years.
The evolution of vascular plants with complex root systems around 450 million years ago was a major factor in drawing carbon dioxide out of the atmosphere, but Gibling and Davies think these plants were also critical in breaking down rock to form the minerals and mud that helped river banks to form. I went to their paper in Nature Geoscience to look at their views on the interplay between organisms and their physical environments (the growing discipline is called biogeomorphology). The researchers identify a series of changes in Palaeozoic fluvial systems forced by plant evolution, including the introduction of stable muddy floodplains well suited for vegetation and soil development.
The authors see plants acting as ‘geomorphic engineers,’ creating a framework for the complexity of further life:
…the development of meandering rivers with strengthened banks through the Late Silurian and Devonian promoted stable muddy floodplains partially protected by levees and highly suitable for vegetation growth and soil development, including carbonate-rich soils… Early Pennsylvanian suites of narrow fixed channels on muddy plains and of island-braided styles in sand-bed rivers imply an increased length of channel margins and riparian corridors with their varied plant communities and subsurface water prisms, which are of crucial importance for many animal species. The Devonian to Pennsylvanian development of avulsive channel systems generated abandoned channels suitable for organic occupation, especially during dry periods. Towards the sea, concomitant expansion of muddy coastal plains and deltas would have also had many biological consequences. Feedback loops are likely to have been complex.
And so on. Just how valuable was this interplay between plants and the physical environment? This entire issue of Nature Geoscience is devoted to the question, noting how many of Earth’s environmental features were brought about by the evolution of life. The effect of plants goes beyond geochemistry and extends deeply into the landscape, controlling the stability of river banks. Before plant life was ubiquitous, water flowed in broad sheets with few clearly defined channels and floodplains. The editors of the journal think this has implications for exoplanet life:
Even if there are a number of planets that could support tectonics, running water and the chemical cycles that are essential for life as we know it, it seems unlikely that any of them would look like Earth. Even if evolution follows a predictable path, filling all available niches in a reproducible and consistent way, the niches on any Earth analogue could be different if the composition of its surface and atmosphere are not identical to those of Earth. And if evolution is random, the differences would be expected to be even larger. Either way, a glimpse of the surface of an exoplanet — if we ever get one — may give us a whole new perspective on biogeochemical cycling and geomorphology.
Let’s hope that we are indeed able to get that glimpse, and a glimpse at many of the exoplanets being discovered today, particularly those in their star’s habitable zone. It’s hard to argue with the belief that evolution will take a wild variety of courses depending on initial conditions ranging from planetary atmospheres to, as we saw above, axial tilt. What we have ahead of us stretching far into the forseeable future is the chance to begin cataloguing exoplanet ecosystems that we’ll learn more about from spectroscopy and eventual imaging as we tune up our tools. We’ve already learned how wildly one planetary system can differ from another. We can only imagine the extensive range life will take, assuming it’s out there, as it fills each unique niche.
The paper is Gibling and Davies, “Palaeozoic landscapes shaped by plant evolution,” Nature Geoscience 5, 99-105 (2012), published online 01 February 2012. Thanks to my friend Antonio Tavani for the heads-up on this paper and the related story from Scientific American.
….axial tilt of as little as 40 degrees would provide a tough environment for complex animals because of the exceedingly hot summers and cold winters that would prevail over much of the globe.
Oceans would be a moderating influence for oceanic life. We already know that complex life forms have all sorts of adaptations to avoid environmental extremes, especially temperature and water availability.
Biology constantly throws up surprises (e.g. extremophiles) that would make me very wary of suggesting that obliquity could be a “complex life killer”.
I do expect evolution to create very different life forms from those on earth, although I suspect that convergence will make some appear superficially very similar to those on earth.
A couple of years ago researchers studying the Cryogenian Epoch suggested that the colonisation of land by lichens about 800 Mya created the first soils and caused the oxygen spike that allowed the rise of large animals. Just recently sponges have been found in Namibia IIRC which date to the Early Cryogenian at 750 Mya, strengthening that possibility IMO. Thus the Ice Ages associated with that era might be related to biological activity just like the rise of more advanced land plants seems to be the cause of another set of glacial advances in the Ordovician.
Would observations of places like Mars and Titan (which had/have liquid flowing at the surface) give us any relevant information? It will be decades or centuries before exoplanets can be observed in that kind of detail.
Very interesting, but I do have a problem with some of their conclusions. Plants leading to the creation of river channels, allowing for the development of soils? Have these guys ever seen a picture of the surface of Mars or Titan, or hear of erosion. If there was wind or water around before the plants, then erosion had been happening for billions of years prior to the Cambrian explosion.
I’m highly dubious about high axial tilts rendering a planet uninhabitable. When a planet with a very high axial tilt has one pole pointing at its star, atmospherically it is an analogous to being tidally locked, and weather simulations of tidally locked planets show they are quite habitable.
I read “Thanks to Plants, We Will Never Find a Planet Like Earth” a while ago and I found it a bit dumb when it seems to attribute rivers to plants.
As Tom, NS as well as comments on the SA article as well rightly point out, both Mars and Titan seem to have rivers.
That plants have an effect on the shaping of Earth surface it’s pretty bloody obvious too.
What kind of modelling did Heller use to arrive at the cyclic sterilisation conclusion? Depending on atmospheric density or ocean distribution it should be possible to mitigate the extreme climates on high-obliquity planets.
A lot of such “Rare Earth” conclusions seem to be predicated on being able to change one factor of the planet in isolation, without that having knock-on effects on other properties of the planet. A similar argument could be that if cars had smaller size wheels, then they wouldn’t touch the ground, therefore only one design of car is possible. But if changing the wheel size would cause the car to be closer to the ground because of the effect of gravity…
Also see Williams and Kasting (1996): in the outer regions of the habitable zone, high obliquity should be less of a problem because of more efficient heat transport around the planet.
Actually the most important living structure in terms of size and environmental impact are probably the massive coral reefs supported by animals that incorporate calcium carbonate into their structures.
Could a planet with a tilt like Uranus be tidally locked around a red dwarf and still spin? The same side would always face the star, but the spin would give the planet a magnetic field like the earth. If so I’d speculate that these types of planets might be the most common place to find life in our galaxy.
Agree with all of the comments, none of these “rare Earth” arguments are credible. Heat can be transported around, so can life forms. Not only that, living things can migrate with seasons, and hibernate, and form seeds, and so on … On Earth there are plant seeds which can only germinate after they have been in a fire.
Yes, this article seems to be all Rare Earth nonsense. One possible explanation of why a decrease in axial tilt caused complex life to evolve is that it simply broke a regular pattern and forced adaptation to radically new environments. If early Earth had little axial tilt then a dramatic increase in tilt could have caused complexity to evolve instead. As said above, Titan and Mars has sandy (sand of pulverized ice in Titan`s case) riverbanks, and atmospheric density and oceans can moderate. Other moderating factors, apart from high percentage of strong greenhouse gases, can be strong storms created by temperature differences. That need not be fatal at all. In fact, it may force lifeforms to evolve hands to cling with, hands that may later help the evolution of intelligent life. Especially if those storms form vast storm alleys but not global storm, which leaves areas to which storm-adapted beings can migrate to free hands (and have more loosely lying objects to manipulate, though breaking parts from clingy plants would be possible in storm zones as well). There is indeed multicellular animals living in extreme temperatures like hydrothermal vents. On the other edge, other animals have antifreeze in their bodies, and many trees have too. Whether or not extreme body temperatures and adapted biochemistries are condusive to intelligent brains is an open question that will not be answered until we can take the temp on aliens, but even if it was impossible, insulation or cooling could evolve to solve the problem, of course gradually enough for biochemistry to keep up with the change. Would they realize that evolution is too complex for a parsimonious tree of life earlier than earthlings?
Like others, I found the article (which I already learned about before) useful, interesting, but also rather speculative and extreme in its assertions (that plants would determine rivers more than geology). And partly also repeating the know and obvious (that plants shape the surface).
I agree with Alex Tolley that evolutionary convergence (similar environmental conditions create similar forms and functions) should not be underestimated! After all, it has led to independent repeated appearance of pretty complex forms and functions here on earth as well. And similar ecosystems.
I suspect that light and temperature, in combination with water and the availability of essential nutritional elements will play a more decisive role in this.
There are very long, narrow channels and rivers on Venus, and those were formed by flowing molten lava!
http://en.wikipedia.org/wiki/Geology_of_Venus
Either that or some very tough sulfur-eating creatures roaming the roasting landscape.
Orbital eccentricity could mitigate some effects of high axial tilt.
Life in Arctic regions does okay with long periods of day and night.
Underground ecosystems might become more complex.
I know this is not a complete answer, but I am certain that at least some of those who declare there is no other life in the Universe beyond Earth are doing so out of religious reasons (We are God’s Special Chosen Children, Jesus would not be sent to thousands of other worlds to save the souls of those sinful inhabitants, etc.) and political ones (those in power on Earth fear the idea of species that make them look like insects and could be removed just as easily).
And these groups tend to have more influence on and bigger voices in our society than professional scientists. They are of the same type that denies evolution and global warming despite all the evidence. Humanity has a long way to go to grow up in this Cosmos, if it can even get that far. Or maybe we are only meant to create the species that will succeed in the Universe.
So, we must accept without scientific evidence the mantra that life and possibly complex organisms are not rare to be considered in the know? Intolerance for skepticism, as those asking “where’s the evidence?” are conveniently labeled “deniers” a pejorative carefully chosen to associate those awful skeptics with Holocaust deniers.
INTERESTING TO SEE HOW EVERYONE AGREES TO DISAGREE.
LISTENING TO ARGUMENT IS ONE WAY TO LEARN MANY THINGS.
NOW…WHERE IS THE VAUNTED GALACTIC CIVILIZATION?
TWO HUNDRED MILLION YEARS SHOULD HAVE BEEN ENOUGH.
OR HAVE THEY DEEMED EARTH TO YOUNG AND UNFIT TO JOIN?
AND BY WHAT CRITERIA?
JAMES D. STILWELL
“I am certain that at least some of those who declare there is no other life in the Universe beyond Earth are doing so out of religious reasons”
The frequency with which I see this irrelevant point raised (as well as calling people who argue that abiogenesis is very rare in the universe “creationists”), on top of the tenacity with which they hold onto their beliefs in the face of the vast astronomical evidence to the contrary, strongly suggests that the galaxy-filled-with-aliens view is itself basically religious in nature. A spin-off of sci-fi, like UFOlogy and Scientology. Indeed, if you listen to late-night radio in the United States, you will find that there’s a strong correlation between people who believe in aliens and people who believe in more traditional heavenly beings. They both have a religious itch that they have to scratch, regardless of the evidence.
I can but agree with previous comments. Well said everyone!
LJK
do not blame the Christians. the majority of scientists are at least agnostics and large number ( me included) are Christians or follow other spiritual beliefs. we believe in evolution, in the possibility of extraterrestrial life and that the earth is NOT the center of the universe. many of us are also brave enough to accept the universe as it is and not try to deny scientific evidence that refutes traditional beliefs about the PHYSICAL universe. If you care to understand how this is possible read some of the writings of C.S. Lewis. There are there are plenty of nuts who claim to be Christians – but also plenty of non Christians who are also nuts. There are other groups – Islamist, Jewish or Buddhist who are also singled out for blame at one time or another. I would defend them as well. .. Move on.
For me the physical universe was created by physical events and can be explained by physical means, but how ever thee universe was created, it was made in a way that life was possible , in fact a direct and expected outcome as the universe evolved. that is pretty amazing! that is not intellegent design, just a physical property, not so different from the spontaneous formation of stars from molecular clouds. I do observe that the universe has no unique processes, that phenomena that happen in one part of the universe can happen in other parts. whey should the formation of life be any different?
The idea that simpler life is all that would develop in a difficult environment is a strange one. In our biosphere complex life relies on these difficulties for its advantage, and when things get too good, such as when lots of wonderful nutrients are poured into a stream, lower forms seem to take over. Do these authors expect our system to be the anomaly, and if so why?
jkittle said on February 9, 2012 at 15:47:
“LJK – do not blame the Christians. the majority of scientists are at least agnostics and large number ( me included) are Christians or follow other spiritual beliefs.”
I blame ignorance and fear, which comes in all stripes. I blame humanity not advancing far or fast enough because of these two traits. They may be fine for the time when we didn’t know what was outside the cave and certainly our society is still set up so that too much knowledge is looked down upon and fear is used as a tool to keep the masses in check.
Note how often fear and ridicule come up when the topic of alien life is presented. ETI are oftem mocked as silly and even unbelievable concepts, mirroring the ancient view that humanity and Earth are the focal point of existence and echoing Plato and Aristotle’s view that there are no other worlds or life than us and our planet – for which they had no serious clue about the true nature of the Universe.
The other great reaction to alien life is fear. How many stories about ETI involve them desiring to conquer or destroy us in numerous ways? Of course there is the other extreme where aliens are treated as angels and gods who will come to save us from ourselves. In either case, such actions require a level of motivation, effort, and resources which make little sense in a galaxy of hundreds of billions of star systems with worlds to choose from.
Note how ETI are almost always viewed in relation to what they might or can do to or for us, not whether they may have their own unique motives or thoughts with no relation to our species for good or bad. Even in our search for alien planets, we seem most interested in worlds like ours with thoughts of future colonization. The possibility that planets which may be like Earth would also mean having native life forms, including smart ones, seems to come belatedly and is not addressed as it should be. How ironic if humanity becomes what we fear, galactic conquerors.
I will not apologize for addressing what I see when it comes to humanity’s reactions to alien life. It is not a few isolated examples and it seems to be something that is becoming even more negative in relation to how our current society is fairing. One might think that the idea of other intelligences would be uplifting and exciting, and I know it is for those who are educated on the subject, but sadly that group is currently in the minority.
I think it’s been mentioned before, but there’s some possibility that “shadow biospheres” (life that originated separately) exist on Earth.
http://www.mso.anu.edu.au/~charley/papers/DaviesetalShadow.pdf
Until we can explore other planets (especially exoplanets) much more extensively than we’re able to today, the only way to address some of the questions raised above is to start looking in the place we CAN look now — here.
“when things get too good, such as when lots of wonderful nutrients are poured into a stream, lower forms seem to take over. ”
Sometimes yes, sometimes not. There are many areas rich in wildlife (fish, birds, etc.) in formerly desert areas. This thriving of higher forms of life in previously inhospitable places is made possible by the farm run-off of irrigation water, enriched in nitrogen, phosphorous, and potassium. These three elements are scarce relative to the requirements of living things on our planet, and water is scarce on land.
Back to the topic of the post. I welcome and enjoy the intellectual flights of fancy that such speculations (axial tilt, etc.) promote. Why not? Are we to do nothing and be timid in our extrapolations? I think not.
But we need to remember that our scientific ignorance is vast on these topics. What we thought we knew about solar systems a scant 20 years ago has been totally trashed as hot Jupiters and a host of other observed extrasolar planetary system facts have made garbage of the computer models that Carl Sagan touted. Not a slam at Carl. Once again, scientific observation has made fools of the theorists.
it is true that if we encounter alien life ( alien to us, we are “alien” to them)
it will be supremely interesting If is a simple life form we can study it biochemically and genetically. If we encounter a civilization, they may not be all that interested in dominating us and there are plenty of resources in deep space so they do not need to take ours. most likely outcome will likely be that they will want to study us -and we them.
We face various environmental challenges here on earth that threaten our future and our ability to support exploration.
Perhaps any culture able to support interstellar travel has already faced these problems. In order to overcome them, perhaps they have to develop a set of ethics that would then serve to guide their interactions with other life forms . this may argue that the paradox we face is simple to solve. Cultures that destroy their own planets do not develop interstellar travel. No species is contacted until they develop a ethic to govern their own actions in a contact with “aliens”. Pnce we are able to control ourselves and perhaps develop interstellar travel on our own, aliens may be willing to talk to use
Maybe Gene Roddenberry got it right!
Nick, I am only interested in the relative advantage of higher life to simpler forms. As such, in the desert to oasis transformations you describe, you would have to give an indication that this ratio has been raised at some point of increasing nutrient levels, and I don’t see that.
I will give a second example of the effect of improving conditions. As terrestrial humidity increases and other variables are kept constant, fungal, bacterial, and vascular plant growth rates all increase. Crop yields at first increase, but eventually they dive due to the even higher growth rates of those lower forms. From what I have seen there is no point at which diseases free plants do not increase their yields along this trend, so I postulate that this collapse is entirely due to the ratio of advantage continuously increasing.
A clear counterexample were easing conditions boosted higher forms more than lower ones would be much appreciated, since I can not think of even one.
@ James D. Stilwell
biological (~ bacterial) life ? complex (~ eukaryotic) life ? multicellular life ? intelligent life ? tool using life ? electronic civilizations ? technological civilizations observable at interstellar distances
Biological life could be everywhere, but the commonality of life could drop one or more orders of magnitude at each level (especially the last level), reaching probability zero for Dyson Sphere civilizations.
Earth, billions of years of life, only a handful of tool using species, ever (even counting the crows from New Caledonia), 100 years of electronics, and still no signs if civilization detectable by alien astronomers.
philw1776 – page 209 of “Cosmos” has various star systems outputted by Sagan’s modified version of Stephen Dole’s ACCRETE planet-formation program. Systems D & E have a Hot Jupiter and a Hot Neptune some 0.5 AU from their stars. I would say Sagan’s program has held up fairly well. It was simplistic and both Sagan & Dole knew that, but it wasn’t overly wedded to the dogma that Jovians only appear past the “Snow-line”.
I largely agree with ljk, particularly February 9, 2012 at 11:06;
the issue here is NOT what people wish to believe or not, regardless whether that is a traditional religion, a ‘new’ or pseudo-religion, or even a desired ‘belief’ in aliens. People are free to do so.
The issue here is the advancement of unbiassed scientific research and discovery through which we *learn and discover* about the universe, regardless of people’s preferred beliefs.
And, as ljk was rightly arguing, it is often people’s preferred private beliefs and political preferences that put that scientific advancement at stake.
To put it in slightly different, even simpler words:
The universe is completely indifferent with regard to our belief systems and if it appears to differ in certain ways from what we believe, well, then that is very regrettable for those beliefs.
But universal reality as well as our reality are ultimately not determined by what we belief to be true, but by what we *discover* to be true. And the universe is ours to be discovered, not just dreamed about or believed about.
I had best slightly expand – as my congratulations arrived a couple of posts lower down the list that it appeared when I was writing it!.
LjK – I think you make a very valid point, that i would personally expand somewhat.
My perspective is that faith based behaviour seems to be a widespread charateristic of humanity. By this I mean an unquestioning belief in a particular idea regardless of the evidence. Richard Dawkins argues this point in his book ‘The God Delusion’. A good example is political ideology, which at the extremes has characteristics of absolute belief and extreme hostility to other points of view.
So to, alas, is normative science. Within the current paradigm we can usually come moderately close to critical rationalism, albiet with a fair dose of egotism and petty rivalry getting in the way. Outside of the current paradagim no evidence will convince some people until, as Kuhn pointed out, the old paradigm collapses, e.g:
1968 – Colorado Commission found that UFO reports contained nothing of scientific value
1983 – Lockner et al (Nature – would have to look up the exact reference) found that Tectonic Strain Lights, or Earthquake Lights actually exist, after proponents of this idea had been ridiculed for years. These are naturally forming atmospheric plasmas related to areas / periods of tectonic strain. Plasma can reflect radar in certain circumstances and appear clearest at night as glowing balls of light that bob around in response to electromagnetic and atmospheric effects – if moving they can be streamlined into a lenticular or disk like shape.
1976 – 1990 A series of papers by Professor M Persinger and Dr John Derr establishing a correlation between UFO reports and areas / periods of tectonic strain.
Conclusion – Both extremes of the UFO debate were wrong. The skeptics totally so and the ‘true believers’ certainly largely so. Both absolutely believed and continue to believe their respective positions. I have less sympathy for the scientists in this – we really out to know better.
Rob Henry, the higher life forms are utterly dependent on lower life forms. Without nitrogen-fixing bacteria, for example, they wouldn’t be able to make proteins or DNA. Life must have originated in an environment rich in ammonia, urea, or similar, but life since c. 3 billion years ago depends on splitting the very strong dinitrogen bond, a trick which can only be done by a unique enzyme that only evolved in certain bacteria, possibly only once. More fodder for the Drake Equation, actually.
Also, that crop yield curve depends on where the crop originated. Most crops (e.g. wheat, corn) evolved far from the equator, and naturally give better yields in climates similar to where they evolved. Others like sugar cane evolved nearer the tropics and give better yields in the tropics.
One obvious climate condition that boosted higher life forms was the increase of oxygen in our atmosphere, providing a source of energy.
While any scientific hypothesis must be rigorously tested by observation and experiment, the sources of scientific inspiration can be almost anything. Newton’s occult beliefs (“as above, so below”) may be in part what led him to look for a theory of universal gravitation. The person who discovered the chemical structure of benzene was famously inspired by a dream. Bohr apparently developed his model of atomic structure after reading about Kierkegaard’s “leap of faith”. None of this is an argument for giving the occult or religion a place in science itself, but rather suggests that scientists should not be too narrow in their education or thinking.
Nick said on February 9, 2012 at 14:18:
[Quoting LJK] I am certain that at least some of those who declare there is no other life in the Universe beyond Earth are doing so out of religious reasons.
“The frequency with which I see this irrelevant point raised (as well as calling people who argue that abiogenesis is very rare in the universe “creationists”), on top of the tenacity with which they hold onto their beliefs in the face of the vast astronomical evidence to the contrary, strongly suggests that the galaxy-filled-with-aliens view is itself basically religious in nature. A spin-off of sci-fi, like UFOlogy and Scientology. Indeed, if you listen to late-night radio in the United States, you will find that there’s a strong correlation between people who believe in aliens and people who believe in more traditional heavenly beings. They both have a religious itch that they have to scratch, regardless of the evidence.”
Actually, Nick, in addition to my view on alien life being based in part on the scientific evidence that does exist in support of it (complex organic molecules, lots of planets, extremophiles, etc.), I also base my view on the possibility and hope as stated by George Taylor (aka Charlton Heston) in the original and best version of The Planet of the Apes from 1968:
“I’m a seeker, too. But my dreams aren’t like yours. I can’t help thinking that somewhere in the Universe there has to be something better than man. Has to be.”
Now we just have to hope we don’t end up with the Statue of Liberty half-buried in the sand and then get captured by a bunch of crazy telepathic mutants who worship an atomic bomb.
Joy: “the commonality of life could drop one or more orders of magnitude at each level (especially the last level), reaching probability zero for Dyson Sphere civilizations. ”
The “more” certainly has to be much more than 1 order of magnitude. Collectively, the 10^11 observable galaxies contain, as a reasonable guess, 10^20 planets, giving us say 10^18 habitable planets where life could have originated. So to achieve the observed results (no civilizations that alter most of the surfaces of their galaxies in any of those 100 billion galaxies), we need 18 orders of magnitude of improbability. Even if, say, we have five other factors in the Drake equation where only 1 in 10 make it, that leaves the origin of life per habitable planet at a probability of 10^-13. Which means, with high probability, no other independent origins of life within our own galaxy.
Joy BTW I’m waiting for you to describe more specifically your intriguing but vague theory about how self-reproduction in connection with high tech manufacture (or at least manufacture of solar cells or fusion plants) is impossible (or at least, in my version of your hypothesis, may require an economy too large for a starship), limited somehow by the laws of physics (laws of thermodynamics? Complexity?)
Nick don’t believe the propaganda, oxygen is a nasty toxic gas that destroys a wide range of organic materials (some of them vital to our entire ecosystem as nitrogenase), and the correlation of elevated levels with the rise of multicellularity rather proves my point. High energy metabolism could equally be based on very high levels of hydrogen, but there is a difference. Hydrogen is a naturally so much more benign, that even complex creatures who have not evolved in its presence, such as humans, can tolerate high levels of it. If our system had been powered by hydrogen you would have had a point.
Higher life on Earth might have evolved to depend on lower forms, particularly bacteria, and ecosystems might begin to collapse without them, but I am only interested in how strong that drive to higher forms is. Adding complexity over an evolutionary pathway adds a heavy extra price, and this must be payed for somehow.
I put it to you that by Earths example we can see many areas where there are such extreme benefits that they exceed that complexity cost. Those massive seasonal temperature swings look like they provide even greater advantages.
PS. You set me thinking. I wonder that if we continually sprinkled tiny quantities of vital bacteria onto the Sahara, would large communities of higher life supported by fields of cacti start sprouting everywhere?
“oxygen is a nasty toxic gas…”
That it is, until it is adapted to. And indeed adapting nitrogenases (those crucial dinitrogen splitting enzymes) to a world with an oxygen atmosphere required some glorious hacks. But it is also an energy source. Oxygen combined with carbohydrates provides far more energy than carbohydrates alone.
“High energy metabolism could equally be based on very high levels of hydrogen.”
This is an intriguing idea — do you have a good reference?
“I wonder that if we continually sprinkled tiny quantities of vital bacteria onto the Sahara, would large communities of higher life supported by fields of cacti start sprouting everywhere?”
Um, no. Deserts are indeed a big piece of evidence against your theory. To bring deserts to life with higher organisms, one needs to add not only the support system of lower organisms but also the scarce resources: water, nitrogen, and often also potassium and phosphorous. The more of these relatively scarce building blocks of life one adds, the more of both lower and higher life forms you get.
Also extreme environments like geysers and deep caves, where there are thriving colonies of bacteria but no higher life forms, are evidence against your theory. Higher life forms require a narrower range of conditions in which to thrive.
And when a new volcanic island gets colonized, as they always do per the Malthusian imperative, it tends to proceed from lower to higher: extremophiles and nitrogen-fixing bacteria first, then lichens, then higher plants, and only then animals. It is the ecosystems consisting of lower organisms that survive better in the initially harsher conditions and pioneer the colonization. (Panspermia if it’s possible would have to work like this too).
Nick, I admit that I have no reference to the potential for high energy ecologies based on hydrogen, but I have based it on just the same observation that you have made for oxygen: hydrogen combined with carbohydrates provides far more energy than carbohydrate alone. You may be thinking that this is still just one third the energy of its oxidation, but it would also be three times easier for plants to generate it in a reducing atmosphere.
I think you are right about other difficulties involved in bringing life to the desert, but I love to speculate, and I always realised that was a big one.
The only part of your reply that I can’t comprehend is how you could think geysers are difficult environments. Lets see – we have water filled pools kept at even temperatures that are protected from diurnal variation, loaded with vital minerals and continuously fed with high energy compounds that could be used as food.
Finally I want reiterate my agreement with your confirmation that, on Earth, higher life relies on lower forms. This does not mean that in difficult environments, such as on land, tracheophytes provide many orders of magnitude more photosynthetic energy capture than all types of bacteria. You have not yet convinced me that examining succession as if it were not a transient condition is useful.
Much earlier NS noted the possibility of a shadow biosphere. When ljk paid due deference to my hatred of the paradigm approach to science, it inspired me to add the following.
Our extreme ability to protein sequence and DNA sequence our known type of life could exasperate the problem of finding a shadow biosphere. Repeated analyses have failed to give an answer to the red raid of Kerala, other than it contains macromolecules that are built from some amino acids, it contains very high levels of aluminium, and at least two groups believe that it grows at super high temperatures. This should have created a tempest of interest in proving or disproving its actual nature. To me it is like a festering boil on the complexion of biology that, so far, it has not excited much interest.
One thing about obliquity is it’s stability.
It was thought the moon was responsible for the stability of Earth’s tilt, but recent research shows that the moon is only a partial player.
Other planets in the Solar System, Jupiter for example, play a role.
Exoplanetary system could have a very wide range of obliquity stability depending on orbital configurations and exomoon possession.
Celestial mechanics will be busy for years.
(By the by the Earth’s obliquity is pretty stable.)
@Nick: Your claim that all higher life depends on lower life may or may not be factually true, but it is not necessarily so. What is definitely needed is autotrophs, but there are complex autotrophs in the form of higher plants. I do not know if nitrogen fixation exists in some higher plants, but there is really no reason why it couldn’t.
Also, cacti are a good example for Rob’s point. Because of their unique ability to store water, afforded to them by their size, i.e. complexity, they can conceivably live where nothing else can.
Although not autotrophs, penguins and polar bears are an interesting example, as well. They live in an essentially dead environment, and derive their sustenance from occasionally dipping into the complex ecosystem in the ocean around or below the ice. Only their mobility, i.e. complexity, allows them to do that. Primitive organisms are constrained to mingle with all the others in the water.
The problem with this beautiful idea is total disregard of the timescale. The first aliens to “visit” “us” would have arrived here billions of years ago, when there would have been nobody there to study, nurture, protect, ignore, or hide from. Instead, what they would have found is a pristine solar system, suitable real estate for a space-faring race to colonize and turn into a thriving new world.
The high obliquity of the early Earth solves the Faint Young Sun paradox, referring to the fact that a low-obliquity Earth would have been permanently frozen back when the Sun only had 70% of its current luminosity. The well-known biochemical signature of a high-temperature origin of life, also paradoxical, turns out to be due to the summer extremes of water temperature in the high-latitude oceans. High obliquity, not Snowball Earth, is the reason for low-latitude glaciations (and only low-latitude). Without high initial obliquity the Earth would have been permanently frozen and lifeless, so I would predict the discovery of icy terrestrial planets but no high-oxygen ones.
As for the pre-Cambrian shift to low obliquity, it was caused by the Gondwana Supermountains, which also were responsible for today’s high oxygen levels and the emergence of vertebrates. Without this fortuitously huge mountain chain an otherwise faithful copy of Archaean Earth would remain at low oxygen levels.
The Rare Earth idea is simply an acknowledgement of the prevailing trend of the last 50 years of science, that everytime there arises a significant discovery about the Earth’s history, it makes our emergence ever less probable, confirming the Anthropic Principle.
Finally, nowhere in all the 100 billion galaxies we can see is there a Type III civilization sucking up most of its galaxy’s starlight. If alien civilization is as likely as the Saganians assert, then there should be plenty of Type IIIs in view, but there are NONE.
Eniac: “What is definitely needed is autotrophs, but there are complex autotrophs in the form of higher plants. I do not know if nitrogen fixation exists in some higher plants, but there is really no reason why it couldn’t.”
It doesn’t. Legumes rely on symbiosis with nitrogen-fixing bacteria, and other plants rely on the nitrogen-rich detritus of legumes to replenish the soil.
Apparently photosynthesis, the Krebs and other oxygen-consuming cycles, and other such major biochemical innovations also originated in single-cell organisms (some of them later incorporated, in the form of chloroplasts and mitochondria, as organelles in the cells of multicellular organisms). Evolution in these higher organisms appears to be biochemically far more conservative, simply retaining the innovations they incorporated from symbioses with single-celled organisms.
This is probably due to (1) the reliance of higher organisms on sexual reproduction, which improves resistance to disease at the expense of preventing radical innovations (since it requires the coordination of two very similar genomes to construct the offspring), and (2) single cell organisms tend to be more R-selected — they have more offspring more of which die. For both reasons single-cell organisms can tolerate more radical mutations when reproducing, which leads to more biochemical innovation.
TO JOY
JAMES D STILWELL
HERE’S THE KEY PARAGRAPH OF THE MICHAEL SHERMER REVISION OF THE DRAKE EQUATION:
“The 60 civilizations in my database endured a total of 25,234 years, so L = 420.6 years. For more modern and technological societies, L became shorter, with the 28 civilizations since the fall of Rome averaging only 304.5 years. Plugging these figures into the Drake equation goes a long way toward explaining why ET has yet to drop by or phone in. Where L = 420.6 years, N = 3.36 civilizations in our galaxy; where L = 304.5 years, N= 2.44 civilizations in our galaxy. No wonder the galactic airways have been so quiet!”
THUS WE HAVE AT BEST 3.36 CIVILIZATIONS IN THE MILKY WAY GALAXY. PERHAPS EARTH IS THE .36. IF EINSTEIN IS CORRECT AND SUPERLUMINAL TRAVEL FOR PHYSICAL BEINGS IS UNLIKELY (REMEMBER RUMPLESTILSKIN’S SPINNING WHEEL AND THE UNLIKELY IMMEDIATE TRANSMUTATION OF STRAW INTO GOLD THREAD) YOU WILL SEE WHY ET MAY NOT COME CALLING FOR A GOOD LONG WHILE: OR PERHAPS THEIR SURVEY SHIP PASSED THROUGH HERE AND FOUND THE DINOSAURS NOT VERY PROMISING. WHICH LEAVES US WITH THE HOPE OF STUMBLING ACROSS THE MONOLITH ET PERHAPS LEFT ON THE MOON FOR HUMANITY TO DISCOVER WHEN WE ARE READY. MANY THANKS TO ARTHUR C CLARKE FOR THAT HOPE. BUT LET’S KEEP SENDING SETI MONEY ANYWAY AND I DON’T MEAN MAYBE. MIRACLES HAPPEN. AFTER ALL EARTH ITSELF IS MIRACULOUS.
JAMES D. STILWELL
There is no evidence of advance life but it is simply not possible to rule it out either. we have to be patient either way. spend a reasonable amount in looking for a signal is ok though risky for the career of the scientists, mainly because the results may take a while and it turns out sucess in science requires being productive and having a lot of (believable) results
imagine writing a thesis that begins ” i spent 5 year looking fr a signal i did not find but they may still be out there”
absence of evidence is not evidence of absence
@ Bill..
I agree with most of what you say, but how do you know there are NO class 3 alien civilisations sucking up their galaxies output?
If done efficiently we wouldn’t be able to see it anyway…