Life Beyond Earth

Raises the a sort of copernican principle, that our framework for understanding life is constrained by our n of 1.

Quotation from p 27:
It is very difficult to deduce what the general properties of a phenomenon such as life might be when one has only a single type of it to study. Imagine the difficulties of a musically naive person in deducing the existence of Beethoven symphonies, Indian ragas, and electronic music, given only a recording of Oklahoma! If several alternative forms of life were available for study, we would have a true comparative biology. We could better decide which properties of matter are necessary, and which incidental, to life. We would undoubtedly learn a lot of fundamental chemistry as well. Almost all of the early discoveries about the chemistry of carbon compounds resulted from the study of materials extracted from living things on Earth. On the other hand, if an exhaustive search of a variety of cosmic environments turned up only further examples of Earth life, it would suggest that our kind of life was the only one that had a reasonable chance of developing or even existing, given the laws of nature.

I again refer to developments in synthetic biology where we are developing alternatives to naturally occuring chemistry and demonstrating that they are viable, which shows they can exist but does not necessarilly consider whether they would arise without our direction.
cf: Neptune's Brood, Charles Stross (and also the precursor book, Saturn's Children, but less so.)
Suggested fiction reading (very short)

Extraterrestrial life might have much better and more efficient ways of doing things that we could learn from.
Oooooh cool - can we talk about the inefficiency and general crapness of natural selection? I'd love that. (SAME. There's no overperformers in evolution; we're all held together with duct tape) It'd take a little while though. I have a lectury bit I can do on that if necessary. We can talk about this any time, but the most natural time would be just before, or during, when we do The Extended Phenotype. (Weird grammar - sorry - but I'll delete this later anyway.)

I.e. If Aliens did invade us they could argue that humans have been doing the same thing to other humans for thousands of years and that it was no different.
Humans have also been invading and killing other species for a long time i.e. dodos. Could just be the next stage in natural selection.
I've never invaded a species. (Joke but also a serious point about grammar. My wife has a whole research project on this. Would we like her to give us a short talk?)

Comparative biology between different forms of life

I can't find it, but someone raised the question of senses we can't even conceive of. I've been wondering about life with phyical processes we don't conceive of, like (for example) an achemical form of life. In considering this I wonder if such a form of life could arise on its own, but even if it could not arise by random processes it could be created by some other form of life that arose by random processes. Again, cf. Neptune's Brood, which I will try to find a copy of this weekend. Cool. Thanks. Also, I think we should make a catalogue of the options here (for senses), and I've got some stuff I'd like to say about unknown physical processes. Also, we'll talk about artificial life when we do Drake's Equation, if not before.

Aliens might have different senses from ours - either a bit different like the shrimp that has much better colour perception than we do, or even radically different, e.g. if there are forces we don't know about.

vision as a mcguffin

CHAPTER 8 - Chemical Life

The love we feel for our planet is natural and analogous to the appreciation we have for our own bodies. (p225)
This is not actually true of all humans, and leads to people blowing things up and otherwise destroying the planet

One example is the question of whether aliens are likely to have an interest in preserving the Earth. The best thing from the point of view of the Fermi Paradox would be if we could think of a reason why aliens should be indifferent to us.

Another example is whether it would be a good thing or a bad thing, morally, for us to establish permanent colonies elsewhere before we blow the Earth up.

A geographer with a predestinist viewpoint might eventually be struck by just how fit the Mississippi River was for its valley. It flows in exactly the right direction, with exactly the needed contours and tributaries, to ensure the drainage of the waters of the central United States into the Gulf of Mexico. In doing so, it passes conveniently by every wharf and under every bridge in its path. (p226)

8.1. Water and other solvents

Notable properties of water: significant heat capacity
Polar character (meaning it's white and fluffy, like polar bears)
They don't specifically note this, but polar character thought to give rise to transient complex structure within water.
They note that water expands when it freezes, which is very weird. But there is no reason it should be essential. This makes it hard for homobiota to space travel.
They don't note that water is amphoteric (can be either an acid or a base) which is very useful for chemistry, but certainly not essential.

Issues with water for space travel: it freeze to form bigger ice crystals; rupturing cells.
Any solvent presents a risk that it could evaporate into the vacuum of space. Maybe this is a problem? You can recapture your solvent as it leaves you, but you're not going to do it perfectly and you're likely to be in space for a REALLY long time, so, problem.
It might not be a problem if you're travelling in an object made of your solvent (like a water ice comet for homobiota, or a methane ice comet for life using an organic solvent).

Esther raises the issue that water expansion on freezing is a particular problem for earthlife, because we have to evolve not to freeze and rupture. A consequence of this is that while water gives a large range of temperatures it is hard to live below freezing point; you need weird special strategies (like reducing the freezing point, or hiding inside rocks and keeping yourself warm with chemistry?).

Proposed alternative solvents:

First, water-like solvents with polar quality, heat capacity, including ammonia and hydrocyanic acid.
Liquid hydrogen fluoride has been excluded on the basis that fluorine is rare, but the F&S note that there are many fractionation and selective concentration processes in nature; e.g. iron is much more abundant in the earth than elsewhere.

8.2. Carbon

Carbon is tetravalent (can form bonds with four other atoms at a time) which allows a lot of combinations for ordering. (Also if you add metals, sometimes you can have more than four bonds, but it's weird because you can also view it as only four bonds but some of them are smooshed out and shared between more than two atoms, or you can even have bonds between an atom and another bond).

F&S note silicon can also form four bonds (although it is very large relative to carbon, which changes the chemistry a lot, they get into this later)
Nitrogen, Phosphorous, Boron, can have three bonds and occasionally four.
Sulphur normally forms two bonds, can go up to six

The authors note that there is no reason to require four bonds. They argue Atoms that can only form one bond can at most form pairs. Atoms that can form two bonds can form chains (or rings), but atoms that can form three bonds can form more complex shapes.

I would note that once you add in metals you can get very weird things where atoms that normally only form (n) bonds can form a lot more bonds. I'm pretty sure there are cases where you can have a hydride ion bound to more than one metal because metals are silly.

That being said, one of the nice properties of carbon is the stability of its bonds. While nitrogen can form a lot of bonds, a chain of nitrogen atoms REALLY does not want to exist; it wants to return to elemental nitrogen in a very loud and dramatic fashion, and it will quite hapilly embed your spectrometer in the wall of your lab when you try to analyse it. But maybe these compounds would be very happy in a much colder environment?

As an aside, if you would like to read an entertaininly written short article on the nitrogen compound that embedded a spectrometer in a wall, it is here and I love it.

F&S note that there is no reason you have to have your structures made out of just one element; chains of mixed elements are perfectly fine. But I would note that if your chains are made of multiple elements you have added a constraint to your system; you now need several things to be availible rather than just one. That's fine but it does add an element of complexity. They note that you could have an alternating chain of elements so that no element in your chain is bonded to itself, which makes nitrogen much happier.

Also, that kind of alternation/variation allows you to make much more specific chemistry because parts of your chain are more reactive than other parts. EG: the phosophorous/oxygen bonds between DNA monomers are much more reactive than a lot of the other bonds, which means that joining monomers together into a strand of DNA is can be done specifically and consistently with less likelihood of accidentally making a bond in the wrong place on a molecule.

Homobiota need phosphorus added to a lot of their carbon chains, and phosphorus is pretty rare, so that illustrates how the trade-off can be worth it.

Fun fact: phosphorus is especially rare in Australia because we haven't had a glaciation event for a very long time, (glaciation breaks up rocks and frees chemicals like phosphorous for use by life) and a lot of Australian plant life has come up with ways to stop using phosphorus in structural molecules because they simply can't afford it. They still use phosphorous where it's chemically important, such as when you need it as a catalyst, but they are quite frugal with it compared to us. This is maybe going to become relevant because we are possibly going to run out of useful phosphorous, given humans just pee it out and it ends up in the ocean. At some point we won't be able to mine any more from fossilised bat and bird urine.

And we don't know whether even weirder things are possible at high pressure. I assume they are, pressure is WEIRD. Most of the planetary environments in the universe are at high pressure (depending on how you measure ... but anyway lots of them are). So the advantages of carbon might not be a big deal compared to the chemistry we don't know about yet.

Carbon is not unique as a basis for generating molecular complexity, but it is very effective. The number of known organic compounds has run into the millions. (p234)

2005 figure estimates the chemical space for organic compounds that weigh less than 160 Da as ~14 million compounds. And that's for very small starting fragments that you would use to build up a larger more interesting molecules; Adenosine (one of the four DNA monomers) weighs 267 Da.

Fink, T., Bruggesser, H. & Reymond, J. L. Virtual exploration of the small-molecule chemical universe below 160 Daltons. Angew. Chem. Int. Ed. Engl. 44, 1504–1508 (2005).

The authors note that carbon dioxide has useful properties; it converts into carbonic acid in water and is therefor readilly availible to circulate throiugh the biosphere both in the oceans and the atmosphere. However they note that phosphorous in the biosphere doesn't ever turn into a gas and still circulates just fine. I also note that a lot of other elements could have similar properties under the right conditions. (If you can get nitrogen away from being nitrogen gas (which is harder but certainly not impossible) it can change between nitrate, nitrites, ammonia, nitrous oxide, and nitric acid, so you have a lot of useful and distinct chemical states.)

But perhaps we should pause first to consider the opinion of Professor Horowitz on previous proposals of this type: "It is not possible to evaluate these proposals because they have not been developed in detail. In the absence of detailed models, all such speculations must be viewed with skepticism." This view is to some extent an outgrowth o£ an attitude held by some biologists, a distrust of theoretical speculation as opposed to a methodical analysis of experiment and observation. (pp235-236)

I think we can all agree that this is very much not true today; biologists (at least on the whole) now love simulation.


I again point out the existence of articial nucleotides, which are still nucleic acids but are in some ways quite different to those naturally occuring in homobiota.

The authors note that amino acids do seem to arise spontaneously, so maybe proteins might be relatively likely to occur. However, other catalysts are possible; many small molecule catalysts exist, some of these are selective. I don't think supramolecular chemistry was a field at the time this was published but it's very interesting here; it involves making useful arrangements of small molecules that can have very specific activity.

The authors note the existence of other macromolecules, such as nylon and cellophane. I would at cellulose and other carbohydrate polymers here, too, particularly as many proteins have chains of carbohydrate monomers that are important to their function. (Though, I think these are usually about specificity rather than catalysis).

They note that many, many polymers can be made in the lab, but we haven't explored the possibility of weird polymers as catalysts very much.

However, chemical theory is not yet in the state where it can predict accurately in advance exactly which giant molecules would have interesting catalytic properties. There would be a considerable risk that the labor invested in the first efforts would yield no positive result. Understandably, there has been no rush of chemists to enter this area of research. The possibility that an alternative set of catalysts could be produced by natural selection on an other world remains a very real one, however. p239

I think this is still the case, and it's a bit of a sociology of science thing. Nobody wants to work on weird polymers that could be catalysts because it's very speculative and expensive, we're much more interested in trying to get structural polymers to form the specific ways we want them to, and we're still getting great results for catalytic polymers by starting with things we understand (proteins) and just changing them in small ways.

cf. Kuhn paradigm shifts, although this is a bit different because we understand that we could investigate these things, but we don't because we're busy.

They note that the key properties of nucleic acids aren't unique to nucleic acids; they work through conventional chemical processes like hydrogen bonding and polymerisation. There is no reason to think they are special.

It is quite likely that many schemes can exist by which other molecules can catalyze their own replication. The functioning of these alternative replicating systems will probably be as complex as that of our own nucleic acid-protein system. It is not likely that we will learn of their existence by theoretical deduction; they must be discovered either by the exploration of the Universe or by laboratory experimentation. p240

This is certainly not true anymore, but they can be forgiven for not anticipating the exponential (?) growth of our capacity for simulation. This sort of thing is exactly what Ball and Brindley are doing; they're working on known molecules but we can just as easily apply it to weird molecules and I'm sure we do.

The labor involved in laboratory efforts to prepare alternative replicating molecular systems, like that needed to prepare other types of macromolecular catalysts, would be enormous. A number of ingenious proposals have been made, however, by the Glasgow chemists, A. G. Cairns-Smith and C. J. Davis. They described a number of organic molecules which, while differing considerably from DNA in structure (some examples lack both nitrogen and phosphorus), could still fulfill a genetic function. pp 240-241

A specific proposal is that life came from organised crystals in clay - crystals as genes that can pass on their imperfections to daughter crystals.

F&S cite A.G.Cairns-Smith and C.J.Davis, The Encyclopedia of Ignorance, eds., R. Duncan and M. Weston Smith. New York: Pocket Books (1977), p. 391. I'm told there's been more work on it but not much. The idea's never completely died but I guess detailed work on it would be expensive.


8.4.1. Ammonia

Ammonia instead of water: it has some similar properties to water (high heat capacity, a bit polar, dissolves salts so reactions can happen), but can be a liquid at colder temperatures. The low temperature means reactions proceed slower, though how much slower is not known. There could be life based on very fast reactions to counteract this, and/or life that's been less active than earthlife ... but it's had up to 12 billion years, so it could still have done a bunch.

Is heat capacity actually important? If we consider things like lethal temperature fluctuations, it could be that it's not a problem in the same way that it's ok if only 1% of gut bacteria survive

Can talk about this in terms of r-selected (lots of babies) versus K-selected (few babies but they're all special snowflakes and you send them to Ormond and look after them really well) organisms. The average number of babies you need to have SURVIVE is 1 (asexual) or 2 (sexual), so either strategy is fine. If heterobiota is often very very r-selected (like gut bacteria) then it can cope with lots of death and therefore maybe it can cope with less heat stability etc. etc.

They make a joke about the danger of freezing being large blocks of ice falling on things, but we don't think that would happen; either the media is small enough to freeze bottom up, or tiny grains of ice would form at the surface and fall down, like snowing underwater, because they don't float long enough to get big. Related: we are pedants.

8.4.2. Hydrocarbons

They talk about life in a hydrocarbon sea. I've always found this idea a little bit fascinating. In earthlife, protein folding is driven partly by a "hydrophobic collapse". Some amino acids are more oily than watery, and when you put them in water they want to clump together (like oil) and minimise contact with the water around them. You could imagine an equivalent process in an oily solvent, like petroleum, where the watery parts of the protein clump together to get away from the oil. If we could get this to work on earth it would be great for industry because a lot of our industrial chemical processes work in oily environments, so protein catalysts are not as viable as we'd like.

The basic difference for a hydrocarbon medium is that it's not polar at all, and hence polar things don't want to dissolve. A lot of the chemistry we're familiar with involves some polar aspect, where positively and negatively charged atoms interact for form new molecules, and a lot of that is dependant on things like dissolved salt ions to stabilise the process. But that's our biochemistry, and we know weird and interesting petroleum chemistry exists, so shrug.

They note that you can imagine oceans made of substances like pyridine which is a great solvent. They note it is big and complicated so a sea of it seems unlikely, but I think you can imagine a self ordering process, or even an event equivalent to the oxygenation of our own atmosphere, in which the hydrocarbon seas were converted to contain a lot of a more useful organic solvent like a pyridine. This kind of thing would be particularly useful because these solvents are mostly hydrophobic but they do have some polar elements, which opens up a much larger chemical space. We can also imagine an encapsulated (ie: cell like) life to synthesise their own internal medium of more useful hydrocarbons, so their interior is suited to their own chemistry. I like this a lot because there are all kinds of internal solvents they could use that are quite similar to each other, so you have a lot of opportunity for interesting variability and selection.

In imagining this, we're clearly biasing our imaginary hydrocarbon sea to be something a bit more viable to homobiota. I think that's useful, but we should also consider heterobiota particularly suited to hydrocarbon seas.

They raise the notion of a process analogous to respiration (but in reverse), in which H2 is used to reduce other compounds. This is like the process used by methanogenic bacteria.

8.4.3. Silicate life.

This is interesting in the cases of very hot planets, their example is 1000°C, where many minerals are liquid.

Silicon is in relativeley low abundance in the universe however is greatly concentrated as silicate on the Earth's crust (rocks)

Silicate refers to silica compounds such as SiO4(4-).
They note that trying to make silica analogues of organic compounds is problematic because silicon bonds much more weakly than carbon (this is because it's bigger, and so its bonding electrons are further from the atomic nucleus, and held more loosely. Sort of.)

They note that if you use silicates as the building block, rather than silicon atoms, you can get some interesting things. They note you can substitute aluminium for silicon, analogous to nitrogen for carbon in organic compounds. There is a lot of interesting mineral and materials chemistry based around occasionally substituting silicon with other compounds like aluminium and phosphorous, or boron, or other things. A lot of semiconductor development is based around occasionally replacing silicon with things that have one more or one less electron, so you can get a material with interesting electrical properties. Maybe part of our ordering mechanisms here could relate to these kind of electrical properties, which (I think?) could result in living circuits. This is not my area though, I might be getting a bit excited.

They note that a large arrangement of SiO4(4-) forms quartz, which would be solid even on their 1000°C world. We can imagine this being used to make rigid structures in more complex organisms, analogous to shells or wood or bones.

They note that this environment could also represent the interior of planets (here life is termed magmobes), but inside a planet there may be less availible energy flows bc no accessible stellar radiation. Surely clumping around a geothermal vent from the other side could be interesting... If there are large temperature differentials, you could get transient higher energy chemicals that could be eaten.

They consider clumps of radioactive material as an energy source.

They consider thermophages, gaining energy by cycling from the higher to lower temperature region of the magma flow. These are quite spatially eparated, and F&S suggest you need a large organism to do this so it can span the distance or swim back and forth, but I don't agree; a lot of these flows are somewhat cyclic, so you can imagine an organism that rides the currents to move back and forth between the hot and cold places. I really like the idea of thinking about that kind of organism, because a similar system might work inside gas giants and stars, which have huge convection currents which would disrupt earthlike ecosystems but which could be really handy if you knew how to ride them. You don't even have to ride them very well; it's like gut bacteria, as long as some of the individuals manage to make the whole journey you can be ok, even if most of them get thrown out to die in the cold place.

Other places in the universe with potential life

Venus- Hell is Home to Demons pg. 335

Venus is slightly smaller than Earth and covered in thick clouds, the surface temperature is 457˚C, the surface pressure is 91 times that of Earth. Venus has twice as much sunlight from being 2/3 closer to the sun than earth is- this small difference is part of the reason that the planet took a vastly different path to Earth.

Phosphorus and sulfur would exist as liquids, which might be a medium for chemical life to evolve in- though very different from earthlife because of the heat that would denature nucleic acids and proteins

Energy might be from the low levels of sun coming through the cloud cover. Venus atmosphere filters 99% of the sunlight before the surface, Earth atmosphere only filters 30%. The authors note that it would be too low level of sun for most earth plants, but why are we worried about what works for earth when we’ve established that the life there would have to have a very different basis. Thunderstorms, strong winds and volcanos do occur readily on Venus and could be used as an energy source

Carbon dioxide is the hmain gas in the atmosphere on Venus. On earth carbon is in solid form, so how it is on Venus as a gas is unknown (cough aliens cough). There are other gases of various amounts including nitrogen, water, sulfuric acid, oxygen and sulfur dioxide. The thick atmosphere leads to the greenhouse effect and the high temperature

Possible life: could have developed earlier in the planet’s history when it was more hospitable (earth is used as the benchmark for "hospitable" here (good point)), and then migrated to the upper atmosphere where the conditions are still like the past. Airbags could be used in the bodies of these creatures like fish have air bags. Or they might float in the constant updrafts that cycle the planet. Initial evolution of life in the gas is unlikely because of low density of matter, but they could have migrated plausibly (also unlikely is not impossible)

Life could develop on the surface in today's conditions and be adapted to the very high pressure. This could be similar to fish and bacteria deep in the sea (where there are a few animals and lots of bacteria, and the pressure is much much greater than on the surface of Venus). Bacteria does not seem to be as big an issue as F&S make out.

The more important issue is energy. Ada notes that their theory about Titan (which will be looked at later) says sunlight can make food-y molecules in the upper atmosphere that fall down to the suface and can be eaten. This makes less energy that active photosynthesising, but it is a possible source.

Jupiter - Where the Action is p.318

Jupiter is a Gas Giant

If we were the size of earth Jupiter would still be much bigger; being a mammoth ball about fifteen meters high

It contains more than 2/3rds the mess in solar system (when you exclude the sun).

It contains most of the matter in the solar system that is in the form of atoms or molecules.

Has over 100 times the surface area compared to Earth, and over 300 times as much mass

Its extreme size suggests that most of the interesting action on the planets in the solar system may be going on there. This suggestion is reinforced by Jupiter's appearance. Its surface is a turbulent mass of clouds arranged in a series of rapidly moving coloured bands

Set among these coloured lights is a unique feature, a large red spot, which has persisted for hundreds of years.

The giant outer planets including Jupiter and also Saturn, Uranus, and Neptune, have retained more of their volatile substances and are composed largely of hydrogen and helium

In the very outer regions, it is quite cold , perhaps —I25°C (I50°K). The hydrogen molecules and helium atoms are spaces quite far apart – the pressure is much lower than at earths surface. As you move closer to Jupiter’s centre the pressure and temperature keep increasing.

Clouds of frozen ammonia surround the planet (firstly salts derived from ammonia then of ice crystals)

Quiet dark. Compared to earth, the sunlight reaching Jupiter’s atmosphere’s top is only 4% as intense as on Earth.

At about one seventieth of the distance to the centre, we reach an area containing water droplets, and the temperatures and densities are comparable to those at the Earth's surface.
The temperature and pressure in Jupiter continue to increase as we descend below the Earth like level.

About 20 percent of the way to the centre of Jupiter, the atmosphere is as dense as water and behaves more like a liquid than a gas. Beyond this, the pressure and density continue to increase gradually until a point is reached at which hydrogen goes into a metallic state in which the electrons separate from the nuclei and roam freely.
The pressure may be three million Earth atmospheres, and the temperature near 11,000°C. If we continue in this direction, we eventually reach a small, rocky iron and silicate core (maybe… or a diamond, or a metallic core….. who knoes, we haven’t been able to access it ... yet) in the centre of the planet, at a temperature of perhaps 30,000°C

Jupiter is a type of mini-sun in itself.

Jupiter emits over twice as much energy as it receives from the Sun.

One possibility for the energy source is the decay of radioactive atoms in the centre, though this may furnish a bit less energy than is needed. Another possibility is that Jupiter is contracting very slowly in size, making its gravitational energy smaller. This loss in gravitational energy is converted into heat. A decrease in Jupiter's size by a millimeter each year would be enough to supply the needed energy, and it would be a long time before we noticed the shrinkage.

life on Jupitor will either have to be able to survive over much greater ranges of temperature and density than occur on Earth, or they will have to support themselves at an approximately constant level in the atmosphere

Therefore, it is possible that solid or partly solid bodies can survive deep inside Jupiter despite the high temperatures, and that such temperatures do not rule out some form of life utilizing these solid bodies. The high temperatures and densities in the deep atmosphere would tend to accelerate the rate at which physical and chemical processes occur, enhancing the prospects of evolving some form of life deep inside of Jupiter.

Moons of Jupitor:
4 moons
Info about 2 cool ones:
lo, the closest to Jupiter, has an active system of volcanoes, perhaps as a result of the strong gravitational pull of Jupiter on lo's interior.

For example, model proposed by John S. Lewis

The surface of Ganymede is made of solid ice. Beneath the ice crust, which is fifty to one hundred kilometers thick, lies an enormous ocean, five hundred kilometers deep. The situation resembles that of our Arctic ocean, but the Ganymede ocean is vaster. There is twenty-five times as much liquid water under the ice of Ganymede as on all of Earth.