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Even though there exists only single data points, I think it is instructive to ponder the following: 1) Life appeared on Earth early pretty much as soon as con

by derekp7 12y ago

Even though there exists only single data points, I think it is instructive to ponder the following: 1) Life appeared on Earth early pretty much as soon as conditions arose that would support it (as soon as the planet cooled enough). So that would point to life being "easy" to form. 2) Biogenesis only happened once (as far as we can tell), so that would point to [a] life being hard to get started, or [b] life was seeded from space (panspermia). 3) It took a really long time for multi-cellular life to appear. So this step appears to be very hard / rare. 4) It took a really long time for nerves ("thinking" cells) to form (and likely only happened once). 5) So far, no sign of microbial life on other planets in the Solar system, so may rule out panspermia from point (1) above.

dragonwriter 12y ago
> Life appeared on Earth early pretty much as soon as conditions arose that would support it (as soon as the planet cooled enough). So that would point to life being "easy" to form. That's quite a stretch. > Biogenesis only happened once (as far as we can tell), so that would point to [a] life being hard to get started, or [b] life was seeded from space (panspermia). Neither one of those conclusions is justified; the first (as I've said elsewhere in the thread) is unjustified because the creation of life changed conditions on the planet -- and its quite possible that it changed them in a way which made it much less likely for biogenesis to occur again. The second is just a completely unconnected conclusion to the premise that supposedly supports it. > It took a really long time for multi-cellular life to appear. So this step appears to be very hard / unlikely. Multicellular life appears to have emerged independently at least several dozen times, so it doesn't seem to be that hard/unlikely (and given the incomplete nature of the fossil record, its possible that it had brief emergences -- possibly early than the known ones -- that didn't last and haven't been seen.) And there has been lots of reversion from multicelluarity to unicellularity that we know of. So, maybe, multicellularity alone doesn't offer much clear a major benefit, so while its not that hard to emerge, there's no real pressure to keep it, until it coincides with the development of some other feature.
- derekp7 12y ago
  >> Life appeared on Earth early pretty much as soon as conditions arose that would support it (as soon as the planet cooled enough). So that would point to life being "easy" to form. >That's quite a stretch. What is a stretch? That life formed as soon as conditions supported it, or that it may indicate that life is easy to form? The earth formed 4.55 billion years ago, the moon formed 4.5 billion years ago, and 4 billion years ago was the end of the late heavy bombardment, and the first formation of life. I do agree that changes in conditions could prevent a second biogenesis event, but there seems to be enough time with the initial conditions that it "should" have happened more than once. But that is just my initial impression from the simplified versions of geologic timescales that are presented in various pop sci media.
ripter 12y ago
Serious question: Biogenesis says that Life creates life or, (I'm paraphrasing) organic matter creates more organic matter. The disproval of Vitalism shows that non-organic matter can create organic matter. Therefore Biogenesis can occur from inorganic matter. So a seed shouldn't be needed. Biogenesis could happen anytime there is organic matter in the right conditions, is that right?

by derekp7 12y ago

dragonwriter 12y ago

> Life appeared on Earth early pretty much as soon as conditions arose that would support it (as soon as the planet cooled enough). So that would point to life being "easy" to form. That's quite a stretch. > Biogenesis only happened once (as far as we can tell), so that would point to [a] life being hard to get started, or [b] life was seeded from space (panspermia). Neither one of those conclusions is justified; the first (as I've said elsewhere in the thread) is unjustified because the creation of life changed conditions on the planet -- and its quite possible that it changed them in a way which made it much less likely for biogenesis to occur again. The second is just a completely unconnected conclusion to the premise that supposedly supports it. > It took a really long time for multi-cellular life to appear. So this step appears to be very hard / unlikely. Multicellular life appears to have emerged independently at least several dozen times, so it doesn't seem to be that hard/unlikely (and given the incomplete nature of the fossil record, its possible that it had brief emergences -- possibly early than the known ones -- that didn't last and haven't been seen.) And there has been lots of reversion from multicelluarity to unicellularity that we know of. So, maybe, multicellularity alone doesn't offer much clear a major benefit, so while its not that hard to emerge, there's no real pressure to keep it, until it coincides with the development of some other feature.

derekp7 12y ago
>> Life appeared on Earth early pretty much as soon as conditions arose that would support it (as soon as the planet cooled enough). So that would point to life being "easy" to form. >That's quite a stretch. What is a stretch? That life formed as soon as conditions supported it, or that it may indicate that life is easy to form? The earth formed 4.55 billion years ago, the moon formed 4.5 billion years ago, and 4 billion years ago was the end of the late heavy bombardment, and the first formation of life. I do agree that changes in conditions could prevent a second biogenesis event, but there seems to be enough time with the initial conditions that it "should" have happened more than once. But that is just my initial impression from the simplified versions of geologic timescales that are presented in various pop sci media.

ripter 12y ago

Serious question: Biogenesis says that Life creates life or, (I'm paraphrasing) organic matter creates more organic matter. The disproval of Vitalism shows that non-organic matter can create organic matter. Therefore Biogenesis can occur from inorganic matter. So a seed shouldn't be needed. Biogenesis could happen anytime there is organic matter in the right conditions, is that right?