= 27d567bc2d48d9f40e9ccc20ea370b15)
evand comments on Open Thread, September 1-15, 2012 - Less Wrong
You are viewing a comment permalink. View the original post to see all comments and the full post content.
= 783df68a0f980790206b9ea87794c5b6)
Loading…= b715d02e85f7b3b4ae65ca3d3e450868)
Subscribe to RSS Feed
Powered by Reddit
= f037147d6e6c911a85753b9abdedda8d)
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (353)
It has become increasingly clear over the last year or so that planets can in fact form around highly metal poor stars. Example planet. This both increases the total number of planets to expect and increase the chance that planets formed around the very oldest stars. (Younger stars have higher metal content). One argument against Great Filter concerns is that it might be that life cannot arise much younger than it did on Earth because stars much older than our sun would not have high metal content. This seems to seriously undermine this argument.
How much should this do to our estimates for whether to expect heavy Filtration in front of us? My immediate reaction is that it does make future filtration more likely but not by much since even if planets could form, a lack of carbon and other heavier elements would still make formation of life and its evolution into complicated creatures difficult. Is this analysis accurate?
I think it's pretty clear that for broad definitions of life, you need carbon or something heavier. It's possible you could substitute boron, but I don't think you can get boron by any process that won't produce carbon as well. You almost certainly need both reducing and oxidizing agents, which means oxygen and hydrogen as the lightest options. There have been proposals of exotic life chemistries, but all the serious ones I've seen substitute heavier atoms like silicon.
The more interesting question is whether you can build more complex life without all the trace elements used on earth. For example, there are plenty of bacteria and fungi that have much lower dependence on heavier metals than multicellular life does, and some simpler multicellular organisms need less than humans do. My unfounded hunch is that you need something that can play the role of phosphorous as an energy carrier, and that it would be hard to find that in just CHON structures. On the other hand, it's possible that even a really poor substitute would offer enough for life to arise, even if it was inefficient, slow, and fragile compared to life on earth: there would be no stronger threat from other life using phosphorous.
The next question is whether metal-poor planets can produce a technological civilization. How important is metalworking in our history? Can you substitute something else for it? Can you get a spacefaring or radio-capable civilization without metals for magnets, wires, and electronics? There are alternatives like organic conductors and semiconductors, but are those accessible without the intervening metals stage? Just how metal-poor are these planets, anyway? Would it be like iron, copper, aluminum, and tin being only as available as, say, nickel is on Earth? Or is silver or gold a more appropriate comparison? Or even rarer than that? Or are they present, but not concentrated into usable deposits?
I feel like I don't know enough about the detailed makeup of these planets to give even a qualitative answer to your question. I'm not sure anyone knows enough about what is required for life to give a good answer. More data about the planets in question will clearly be helpful.