David Toomey. Weird Life: The Search for Life That is Very, Very Different From Our Own. W. W. Norton, 2013.

“Its life Jim, but not as we know it”, is perhaps the only famous line from the song 'Star Trekkin', though the words were never actually spoken by Dr McCoy in Star Trek. Life, but not as we know it is the subject of this book, in which David Toomey meets with and discusses the work of those searching for this weird life.
The start of the search for alien life begins here on earth, with the hunt for life that might have come from a second genesis, one of those involved in this search being the retired cosmologist and one-time ufologist Paul Davies.
All known life is related and shares a common descent from the Last Universal Common Ancestor (LUCA), a microbial life form from some 3.5 billion years ago. However some biologists wonder if there could be a shadow biosphere of things not descended from LUCA at all. The search for this terrestrial weird life is very difficult, because counting all the life forms on earth is next to impossible and the number of species of life as we do know it runs between 3.6 to 100 million (in other words no one really knows), and the children of LUCA occupy a vast and diverse range of habitats, and these seem to continually increase.
Weird terrestrial life might have to be looked for in very extreme environments, and as no-one has any clear idea of what they would be looking for. One possible clue would be to find some super harsh place, where there is life in the gentler parts, then a sterile region, then more life in the really nasty parts, that would very likely be weird life. Other possibilities are that the weird life shares the same habitats as our life, even perhaps in symbiosis with it. Or it, or rather the remains of its activity, might by the cause of strange stuff called Desert Varnish.
Most weird life is likely to be found on other planets, and Toomey takes the tour outwards, into realms of increasing weirdness. Some extraterrestrial life might just be weird because it just isn’t descended from LUCA, but other sorts might have quite a different biochemistry, and Cambridge biochemist William Baines thinks that we have written off silicon life too quickly, and that it might just exist in very cold places. Of course the search for exotic life would be simpler if there was an agreed definition of life, but there isn’t, so if really weird life were found, there may well be very fierce arguments as to whether it is living or not. One can probably say that life in the methane seas of Titan is likely to be weirder than any in the brine oceans of Europa. One general test for life might be disequilibrium in the atmosphere, and it appears that such disequilibrium exists in the atmosphere of Titan, so maybe Titan is full of utterly alien life-forms.
Toomey takes through suggestions of life in the clouds of Venus and Jupiter, before taking on a range of extra solar possibilities, the atmospheres of warm gas giants, their moons, a range of planets, perhaps even life on comets or in the atmospheres of white dwarfs, or perhaps even in cosmic clouds as in Hoyle’s The Black Cloud, or on neutron stars.
Much of this life might be microbial, but what about 'intelligent life'? Here I fear Toomey’s imagination rather falters because we are back in the realms of radio telescopes and intelligent machines. However, really weird life is likely to produce weird minds doing things that are utterly baffling to human minds.
After that little falter, Toomey takes us to the limits of weirdness, with alien life in other universes where the laws of physics are quite different, or perhaps even 'places' where the mathematics is different, or even where there is no mathematics. Of course we should remember however weird this stuff gets, it’s all a kind of weirdness that human beings can at least half imagine or articulate. I suspect that the really weird is going to be even more weirder than that!
That being said this is a good introduction to a fascinating subject. – Peter Rogerson

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