When people look for life in outer space do they only look for planets that are similar to ours or do they look for planets that could produce other forms as life as well. Is it even possible to have another life form that isn’t carbon based?
I think when people look for life, they’re really looking for radio signals from other intelligent beings, and not discriminating on the basis of planetary chemistry – we’re too far away and have too little info on other planets to do that, anyway.
The question of whether silicon life could exist has come up on the SDMB before. Suffice it to say that all sorts of exotic environments have been considered in science fiction – check out the works of Hal Clement and Robert Forward, in particular. Different chemicals, different temperatures, different pressures, nuclear vs. atomic reactions…
And who says life has to be on a planet – read Fred Hoyle’s The Black Cloud.
I doubt whether silicon life forms are possible. Silicon chemistry is now where near as rich or diverse as carbon, and silicon-silicon or silicon-oxygen bonds are not as kinetically stable as carbon-carbon bonds. It might be possible for a silicon-carbon hybrid.
humans have only been around for the last 3 million years. It’s a possibility that organisms have evolved some what independently in the mantel of the earth with different and overlooked molecular structures. If that were the case then I would say that the reason we overlook them is because as they cool their structures collapse.
Has anyone pondered the existence of silicon zombies?
Silicon Zombies – well, they’re good conversation starters.
One big problem is that silicon compounds are not really very soluble under ordinary circumstances – they tend to form crystals that are water-resistant. Most of our crust is silicon compounds. Silicon tetrachloride is a liquiid, but it reacts rapidsly with water, and wouldn’t be something you’d find in a world that had liquid water. The silicones are organo-silicon compounds that were created in the laboratory only a century or so ago, and don’t occur in nature. Quartz is pretty insoluble in neutral water even at high temperatures, and only becomes soluble at high temperatures and in alkaline environments. Sodium silicate is soluble, but I don’t know that it occurs in nature (it’s made by reacting sand with alkali at high temperatures).
In short, you don’t have water as a convenient fluid to use in most silicon reactions at what we would consider “ordinary” conditions. It’s hard for me to imagine life developing and continuing without something like that. It’s possible you could have silicon life under very different circumstances – high temperature alkaline water, say in a volcanic vent, or something. Or high temperatures without any water present. But it would be something very different from our sort of life, and the argument that silicon is like carbon because it forms similar bonds and lies below it on the periodic table loses something of its force if you can’t substitute silicon for carbon under similar circumstances.
In that light, consider the creature described by Stanley G. Weinbaum in his classic 1934 science fiction story “A Martian Odyssey” – it builds a pyramid out of blocks of quartz around itself, then breaks out of it when it’s completed, moves over, and starts the process over again. It’s a silicon being, you see, and the blocks are the results of its “exhalations”, since , unlike us (who exhale carbon dioxide, being carbon-based life), it exhales silicon dioxide, which isn’t a gas, but is a solid. Then think how likely it is that something like that would be a successful life-form.
We have a hard enough time figuring out how to recognize alien carbon-based life. For silicon-based life, if it’s even possible, we haven’t a clue of how to find it.
A chemical array of elements other than carbon, or even other elements and carbon under entirely different set of physical conditions might have all the necessary characteristics to meet our definition of life, if we ignored the fact that respiration, ingestion, digestion, and responses to stimuli were to take place in thousand year periods, rather than in seconds. Imagine the birth of a new generation that took twenty thousand years to happen, after gestation for half a million years. In a few billion years, they might even evolve. A little bit.
Tris
A team around Glaswegian chemist Lee Cronin is currently investigating, from the ground up, the possibility of ‘inorganic’ – i.e. non-carbon – life; see this TED talk.
True but lab based potential doesn’t really help when we’re trying to figure out the best candidates for consideration. We know a subset of the environmental criteria that allows for a proliferation of life to exist - Earth. So we take those things we know - liquid water, G class star and start there. Given the choice to get the telescope time to examine an exo-planet’s atmosphere for oxygen which would you choose? The frigid Neptune side planet going around a M class star or a super earth with potential liquid water?
I have heard that ammonia can take the place of water in life processes for suitable extraterrestrial life.
a) Really? How would that work with carbon-based life?
b) Could that work with silicon-based life?
Radiolarians produce silicon-based skeletons.
This is from the wiki page:
"The main class of radiolarians are the Polycystinea, which produce siliceous skeletons. These include the majority of fossils. They also include the Acantharea, which produce skeletons of strontium sulfate. "
the skeletons of some radiolarians, diatoms and foraminiferans are siliceous but they are still carbon-based organisms. some grasses also have silica (those leaf edges that cut you.)