by Matthew Cobb
The BBC, together with Science Channel, has just produced an excellent five-part series, The Wonders of the Solar System, fronted by my colleague from the University of Manchester, physicist Professor Brian Cox (no, I haven’t met him). Cox is an extremely pleasant presenter who gets a lot of press because he is young (ish – 42), good looking (well, he has a lot of nice hair) and he used to be a pop star (he played keyboards in a band called D:Ream which had a 1994 hit with “Things can only get better”, which was notoriously played at the early morning celebration of the New Labour electoral victory in 1997).
His popularity is justified and undeniable – only three hours ago, one of my ex-students posted on Facebook “loves bryan cox. pop star and a physicist. amazing.” You can find an amusing profile of Cox here.
The series has used some fantastic astronomical images to show how studies of terrestrial geological phenomena can inform us about what’s happening on other planets in the solar system. The last episode in the series, which I have just watched, was on the possibility of extraterrestrial life. [There’s a BBC page about this episode here.] Cox’s focus being the solar system, he didn’t even mention the Fermi paradox (summed up in his question “where are they?” – given the size and age of the universe, the place should be heaving with bug-eyed monsters in flying saucers, but it clearly isn’t). Rather, he was interested in where there might be life in the solar system.
There are two current candidates, apart from our Goldilocks planet (not too hot, not too cold, just right) – the planet Mars and Europa, Jupiter’s moon. There’s a lot of speculation involved, but it’s still fascinating stuff. Europa is covered with ice, but it is continually fractured and shifting, and measurements indicate that there is a massive ocean of salt water underneath the surface – an ocean that may be 100km deep. This is an awful lot of liquid water (more than twice the amount on Earth), and Cox made the case that because we can find bacteria living and reproducing within ice on Earth, it may also be the case that similar organisms live in Europa’s ice-shell.
One problem, however, is that the very size of the ocean may exclude Europa as a source for genuinely alien life, for the simple reason that for life to evolve, it would require a very stable, static, tightly controlled environment for those fragile molecules to come together. And that will be absent in the swirling black depths of Europa’s ocean.
My feeling is that on Earth the evolution of the first self-replicating molecules – probably RNA – did not take place in “some warm little pond” as Darwin put it, but rather in some tiny bubbles in the mud on the edges of such a warm pond, that would be stable and secure enough, for long enough (perhaps hundreds of years or even more). In other words, something like a cell was required before those amazing reactions that produce life could evolve. In Europa’s case, my guess would be that something similar would be necessary (perhaps tiny bubbles in the ice) for replicant molecules to evolve.
The last time I suggested to Jerry that something like a cell (non-organic, of course) came before its contents, he was rather rude, but what does he know? Or me? Or anyone? It is the case that spherical “protobionts” made out fats occur spontaneously, “reproduce” and have semi-permeable membranes that can see various metabolic processes occur, as shown in this first-level undergraduate textbook:
Even more intriguing for me was the section that dealt with something I knew nothing about, and about which other views have tweeted their disbelief about: snottites. These are slimy structures found in some caves, which are formed by archea – simple bacteria – that are able to metabolise hydrogen sulphide (in a dramatic scene, Cox went deep into one of these caves, where the atmosphere was virtually unbreathable, his personal hydrogen sulphide alarm bleeping away), and they excrete sulphuric acid. When these organisms live in limestone caves, they actually help etch away the caves through their respiration.
The fact that I didn’t know about snottites is merely my ignorance (and shame). You can find a great NASA page about them here.
These are not only great extremophile organisms – they look like snot! they crap out acid! – it also reinforces the idea that even if all the conditions currently found on Earth are not met, life may still evolve. Including on Mars and Europa.
This is hardly surprising in a way – when life evolved here 3.5 billion years ago, Earth wasn’t like it is now. In particular, atmospheric oxygen levels were at about 0.0007% of what they are now. It took life itself to change that, in two vitally important events – the Great Oxidation Event (2.5 billion years ago which saw levels shoot up to around 8% of current, followed by another massive surge, up to present-day levels, around 650 million years ago, “shortly” before the Cambrian Explosion. But that’s another story.
Here’s a trailer for the ET episode of The Wonders of the Solar System (may not work outside UK…)
There’s also a great spoof of both Cox and the mind-bending amazingness of the solar system here. The success of the spoof owes much to the imitator getting Cox’s Oldham accent more or less spot on, and folk memories of the drug-crazed ramblings of Madchester bands like the Happy Mondays and the Stone Roses. Warning: contains rude words.
That programme has been great.
Thanks for the link to the spoof, too.
How can you have “non-organic life”? And how can you expect something like a cell to appear without the complex collection of chemicals to assemble it? Are you suggesting that some fairy created the cells and the means of replicating them were filled in by the fairy at a later stage? That’s a bit like saying the Great Pyramid was simply there and the Egyptians turned up later and put it to some use.
You misread me. I suggested there might have been a non-organic CELL-like structure, not non-organic life. It would effectively be like a test-tube. A place where the molecules could meet and do their stuff – being alive. Nothing spooky or creationist about it. Such non-organic structures exist, and show the kind of behaviours we’d expect, as indicated in the post. However, the next step would have been the evolution of a proper indigenous, proteinous cell wall, based on the genetic code in the replicant molecules. This is a perfectly materialist hypothesis, even if a) Jerry hates it, b) it is by no means original to me and c) we’ll never know if it’s true or not. It has the advantage of providing a solution to the complicated biochemistry of life, and quite how difficult it can be to get it work (as anyone who’s tried to do a PCR will know).
“archea – simple bacteria”
NO. Please do not say this.
Archaea are the third major branch at the base of the (Earthling) tree of life – along with the Bacteria and the Eukarya.
Archaea are not Bacteria. Archaea are their own group of living things. They’re mostly unicellular, and generally microscopic (as is the case with nearly all individual cells), and live in pretty much every examined environment, features they share with Bacteria. But they’re quite different in a number of important ways, and are more closely related to us (the Eukarya) and either of us are to the Bacteria.
Mad Scientist said: “How can you have “non-organic life”?”
Non-organic in this context means “without complex molecules formed of carbon bonded to oxygen, hydrogen, nitrogen, sulfur, and / or phosphorus”.
So, a reproducing, metabolising, internally-homeostatic thing made of molecules that are not organic molecules would qualify as non-organic life.
Structures with a stable internal environment form spontaneously under a range of conditions; some of them catalyze the formation of similar structures. The space between layers of mineral clay particles, for example. The molecules required to assemble such structures are things like silicate and various ionic salts such as sodium chloride and magnesium sulfate. Plus a bit of water and the right conditions of temperature and pressure.
“Are you suggesting that some fairy created the cells and the means of replicating them were filled in by the fairy at a later stage? ”
Project much? Your “fairy” is a creator-god by another name. That is not being suggested here.
Mea culpa for the archaea, and thanks for the correction, which should have been more severe.
Yes, what do we know? All these data are up for grabs.
For example, one can do a robust prediction that oxygenating life evolved before ~ 4.2 Gy ago as carbon and oxygen isotope ratios indicate but not conclusively prove. There are geologists that test an oxygenated Earth and no specific oxygenation event on various minerals. While others disagree, obviously. And so on and so forth.
What is more clear is that habitability and actually being inhabited is different things, because biospheres coevolve.
Probiotic and protobiotic life certainly need an energetic environment to drive synthesis and selection. (Such as PAH, which seems photoselected for stability, in such case likely by their aromatic rings quickly dissipating energy to the dust that breeds them.)
Such an unstable and dynamic environment still needs to be sustained over suitable time scales until independent cellular life evolves. While a biosphere with such cells create its own dynamics for better (Last Heavy Bombardment survivability by outbreeding local sterilization events) or worse (say, if a biosphere oxygenation event really happened and killed off most earlier life).
Habitability can be measured simply as biomass production capability. Mendez has a model for this that gives a quantitative index value to compare planet models with. It is tested against Earth, so it should be reasonably sound.
Notably the best candidate is Enceladus (most bioproductivity compared with planet mass), if internal models bear up. Earth squeezes in between before Mars and Europa. The ocean of Titan is a potential “maybe”. And there are a lot more moons with ocean candidates, albeit seldom with putative access to minerals such as for the three mentioned here (Enceladus, Europa, Titan).
It is, I believe, too idiosyncratic to name Mars and Europa “current candidates”. At least Enceladus should be mentioned as well, I believe astrobiologists is considering it.
That is indeed a major theme of metabolism first theories, modulo “before its contents”. A reasonable stage before lipids populated inorganic cell walls are holes, such as in heat vents. A mere constriction serves to set up electrochemical gradients to the environment while allowing material to pass.
I find it immensely encouraging that the LUCA had ATP and its kinases.
First, it co-evolved with chemosynthesis and membranes because AFAIU you need a membrane to scope up free energy to make it work. (ADP-ATP metabolism doesn’t come up even with regards to electrochemical potential on its reactions.)
Second, more or less exactly like the ribozymes that points back to the RNA world the preserved structure in kinases seems to be pockets for two water molecules that work as a catalyst respectively motor molecule. Before being capable of handling metals with proteins or even making proteins, what could a cell metabolism do for enzymes? Rely on topologically trapped water of course.
So FWIW, electrochemical gradients and cells come early. (Well, duh!)
I’m sure there was a catch here somewhere, but I don’t remember exactly. Weren’t they relying on oxygenating species in their environment?
Anyway, I believe that aside from such local gradients as from heat vents and radioactivity you have to backtrack to photosynthesis to argue that you have a potential for a biosphere.
Maybe it is the physicist in me, but I believe we can do better. Yes, there will be many theories (because of many pathways!) that will compete. No, they are still testable and evaluable against measures on theories (such as parsimony).
I think Mulkidjanian et al shows this when they test the Zn world theory. It does pretty well, even though the above findings of water catalysts dis-empower their tests for prevalence of early Zn/Mn catalysts. There still remains 8 or so stronger tests IIRC.
The point is that we know that it is a feasible pathway. Now any competitors have something to measure up against.
Also, while evolution may have taken less likely pathways, nothing says that it did so. In fact, given that there were independent localized trials competing for the LUCA, it is fairly sound to take the most likely theory of those that are testable as the preferred one.
[More problematic is that proposals aren’t considered for robustness. What happens with side reactions or competing reactions and so on? Again, Mulkidjanian et al does a pretty good job of ensuring robustness, but that is a weak untested side to such work.]
The most convincing suggestion for the locus of life’s origins that I’ve seen is a deep sea vent (not the super hot ones), where mineral structures provide the regions of stability for the reactions to get going.
There may very well be plenty of those at the bottom of Europa’s ocean.
I’ve just watched the last episode and couldn’t believe my eyes.
In the last piece to camera he actually did a Sarah Palin! Reading notes written on the palm on his right hand. Mind you, that means he is left handed, so that’s all right ;o)
BTW the series was excellent.
What? No one shouting ‘he oversimplified’?
But if you pitch it at a level that only the informed can understand you lose the meaning of communication.
That does include me BTW.
The youtube linky of Cox and the snottites! http://www.youtube.com/watch?v=KdwS9v8zBpQ&playnext_from=TL&videos=ypgjkUPpJ_c
Brian May (of Queen) is a much more successful musician and also a published physicist.
(yeah, but Brian Cox is a hottie!)
Yeah. I have occasional moments of distraction, imagining him and Ben Goldacre together …