Interesting, but I was more thinking in the “simple life” ⇒ “intelligent life” step than about abiogenesis. As you said, we don’t have any strong evidence about the likelihood of abiogenesis, we only have two weak ones : the fact it happened early on Earth, and the Miller’s experiment which shows that under right conditions, build blocks of life can arise quickly.
But for the “simple life” ⇒ “intelligent life” step, we have even much less evidence. We know it took a long time on Earth, about 4 billions of years. But are we specially lucky (due to the conditions on Earth, and due to random events) ? We just don’t know.
There seems to be many evidence pointing to it not being so easy. Consider a parameter like isolation. If your star is too isolated, it won’t get enough heavy elements to sustain life. Heavy elements like oxygen, carbon (and worse for iron, calcium, …) were not created in significant quantities during the big bang. They were created later on in the heaviest (hottest) stars and in supernovae. So your star needs to be close enough to other stars (inside a dense enough galaxy) so it gets those elements. But if there are too many stars nearby, then some will go nova close to your planet before it had time to develop intelligent life, and will wipe all life (or at least, all complex life). So there seems to be a very narrow range of amount of nearby stars for intelligent to be able to develop itself.
The same goes for the mutation rate (dependant on natural radioactivity, strength of magnetic shield, …). If the mutation rate is too slow, evolution will take longer, and you won’t reach intelligent life before your main star goes giant red or nova. But if the mutation rate is too high, complex DNA will be unstable, and complex life won’t evolve.
The same goes for so many parameters. For each of them, we don’t know much about the acceptable range, nor how likely we are to find it. So… better admit we really don’t know about the odds on simple life to evolve into intelligent life, nor about the average time it would take. Not finding any intelligent life is, to me, strong evidence that it takes time and it requires rare conditions.
I think mutation rate would be subject to evolution as well. We can evolve to do more, or less DNA repair (and checks; up to acute radiation poisoning, cell self destruct is good enough).
Also, the effects of radioactivity are presumed linear. Extrapolating from high doses, the doses of up to 10x our natural background must have extremely minor effect on the mutation rate, vast majority of mutations arising due to other causes.
(The radiation releases in nuclear accidents are only a big deal because very huge number of people is exposed, resulting in massive dis-utility even if cancer rate increase is very minor)
Interesting, but I was more thinking in the “simple life” ⇒ “intelligent life” step than about abiogenesis. As you said, we don’t have any strong evidence about the likelihood of abiogenesis, we only have two weak ones : the fact it happened early on Earth, and the Miller’s experiment which shows that under right conditions, build blocks of life can arise quickly.
But for the “simple life” ⇒ “intelligent life” step, we have even much less evidence. We know it took a long time on Earth, about 4 billions of years. But are we specially lucky (due to the conditions on Earth, and due to random events) ? We just don’t know.
There seems to be many evidence pointing to it not being so easy. Consider a parameter like isolation. If your star is too isolated, it won’t get enough heavy elements to sustain life. Heavy elements like oxygen, carbon (and worse for iron, calcium, …) were not created in significant quantities during the big bang. They were created later on in the heaviest (hottest) stars and in supernovae. So your star needs to be close enough to other stars (inside a dense enough galaxy) so it gets those elements. But if there are too many stars nearby, then some will go nova close to your planet before it had time to develop intelligent life, and will wipe all life (or at least, all complex life). So there seems to be a very narrow range of amount of nearby stars for intelligent to be able to develop itself.
The same goes for the mutation rate (dependant on natural radioactivity, strength of magnetic shield, …). If the mutation rate is too slow, evolution will take longer, and you won’t reach intelligent life before your main star goes giant red or nova. But if the mutation rate is too high, complex DNA will be unstable, and complex life won’t evolve.
The same goes for so many parameters. For each of them, we don’t know much about the acceptable range, nor how likely we are to find it. So… better admit we really don’t know about the odds on simple life to evolve into intelligent life, nor about the average time it would take. Not finding any intelligent life is, to me, strong evidence that it takes time and it requires rare conditions.
I think mutation rate would be subject to evolution as well. We can evolve to do more, or less DNA repair (and checks; up to acute radiation poisoning, cell self destruct is good enough).
Also, the effects of radioactivity are presumed linear. Extrapolating from high doses, the doses of up to 10x our natural background must have extremely minor effect on the mutation rate, vast majority of mutations arising due to other causes.
(The radiation releases in nuclear accidents are only a big deal because very huge number of people is exposed, resulting in massive dis-utility even if cancer rate increase is very minor)
I was just continuing your attack on the common assumptions for the values involved with the Drake equation.