5 ms·

The Red Rain cell claims (even with a question mark to indicate tentativeness) seem particularly bold. It's not difficult to imagine circular structures formin

by rflrob 14y ago

The Red Rain cell claims (even with a question mark to indicate tentativeness) seem particularly bold. It's not difficult to imagine circular structures forming abiotically, and given that there are much likelier explanations for the red rain, I remain unconvinced.

marze 14y ago
If diatoms did arrive in meteorites and are the ancestors of Earthly diatoms, you would think they would have shown up in the fossil record earlier.
- madaxe 14y ago
  Not really. Diatoms are tiny, and under the pressure of successive layers of sedimentation, silica (of which diatoms are largely comprised) will recrystallise at that scale, making detection of fossils difficult, if not impossible. I believe there are Precambrian diatom candidates, but unlike bacteria, which form colonies and therefore can still be found from ~3.5Ga (stromatolites and friends), diatoms are free-floating, and therefore easily lost in sediment.
  - marze 14y ago
    I see. What about candidates for a high silica rock that might have been metamorphized diatom deposits? If this theory was correct and diatoms were the original life form, it would suggest they might be more primitive, genetically, assuming little subsequent evolution.
    - madaxe 14y ago
      Indeed - I'd opine that the meteor in question was probably terrestrial in origin, as diatom genetics demonstrate that evolution is live and kicking in diatom populations. That said, it doesn't exclude the possibility of diatoms having perhaps taken a lengthy space trip at some point in their evolutionary history. It would certainly go some way to explaining why a marine species would have developed to be radiation and vacuum resistant. As to siliceous rocks - possibly, although I don't believe there's been anything found to suggest diatoms in great antiquity as yet. Funnily enough the most prevalent siliceous rock is... diatomite. Your toothpaste is made out of it. Chert (flint, etc.) is probably a better candidate substrate, but again, diatoms of that age would be indistinguishable from the substrate itself. Molecular clocks could indicate a biogenic origin, but as yet there's no way to demonstrate what variety of biogenic origin. There's evidence in terms of carbonaceous inclusions in ancient rocks that suggests the existence of life on earth before previously assumed - http://courses.washington.edu/bangblue/Mojzsis-3.85Ga_Akilia_d13C-Sci96.pdf http://courses.washington.edu/bangblue/Mojzsis-3.85Ga_Akilia..., but nothing to suggest it was diatomic in nature. Anyway. If their evidence isn't falsified, even if this isn't extrasolar panspermia, it's a demonstration that panspermia is possible.
      - marze 14y ago
        You're guessing the rock in question did fall from the sky, but that it was blasted of the Earth previously? Aren't there features of chontritic meteorites that would make it fairly easy to distinguish from an regular rock? Given the incomplete theories on how cellular life got a start, I don't see why people think evolving on Earth is any more likely than arriving from somewhere else. More time and more planets.
        madaxe 14y ago
        Well, they appear to have decided it's a carbonaceous chondrite through visual examination alone - you can only really be sure by whacking it through a mass spectrometer and seeing what isotopes you've got. Either way, I think panspermia is perfectly possible, but the jury's out until this is independently verified.
        marze 14y ago
        Well, if the science community ever decides Wickramasinghe is right I'll laugh. It was interesting to read about diatoms: about 25% of all photosynthesis, more than all the rainforests location on "tree of life" is unclear: "Despite a number of studies to examine phylogeny, using one or several genes, the relationships of diatoms to other groups are still unclear and there is still a huge gap in our understanding of how and when diatoms acquired their unusual morphology and life-cycle characteristics. The diatoms have often been treated as a separate phylum, reflecting their unique features. Pascher (1914, 1921) suggested that the diatoms have features in common with the Chrysophyceae and Xanthophyceae and therefore placed these classes and the Bacillariophyceae in the phylum Chrysophyta. Ultrastructural and molecular sequence data have confirmed the general thrust of Pascher’s idea, placing the diatoms unambiguously among the heterokont protists (‘stramenopiles’) within the chromalveolates (Adl et al. 2005)." and Wickramasinghe has hypothesized interstellar dust might be diatoms(!): "there exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains."

by rflrob 14y ago

marze 14y ago

If diatoms did arrive in meteorites and are the ancestors of Earthly diatoms, you would think they would have shown up in the fossil record earlier.

madaxe 14y ago
Not really. Diatoms are tiny, and under the pressure of successive layers of sedimentation, silica (of which diatoms are largely comprised) will recrystallise at that scale, making detection of fossils difficult, if not impossible. I believe there are Precambrian diatom candidates, but unlike bacteria, which form colonies and therefore can still be found from ~3.5Ga (stromatolites and friends), diatoms are free-floating, and therefore easily lost in sediment.
- marze 14y ago
  I see. What about candidates for a high silica rock that might have been metamorphized diatom deposits? If this theory was correct and diatoms were the original life form, it would suggest they might be more primitive, genetically, assuming little subsequent evolution.
  - madaxe 14y ago
    Indeed - I'd opine that the meteor in question was probably terrestrial in origin, as diatom genetics demonstrate that evolution is live and kicking in diatom populations. That said, it doesn't exclude the possibility of diatoms having perhaps taken a lengthy space trip at some point in their evolutionary history. It would certainly go some way to explaining why a marine species would have developed to be radiation and vacuum resistant. As to siliceous rocks - possibly, although I don't believe there's been anything found to suggest diatoms in great antiquity as yet. Funnily enough the most prevalent siliceous rock is... diatomite. Your toothpaste is made out of it. Chert (flint, etc.) is probably a better candidate substrate, but again, diatoms of that age would be indistinguishable from the substrate itself. Molecular clocks could indicate a biogenic origin, but as yet there's no way to demonstrate what variety of biogenic origin. There's evidence in terms of carbonaceous inclusions in ancient rocks that suggests the existence of life on earth before previously assumed - http://courses.washington.edu/bangblue/Mojzsis-3.85Ga_Akilia_d13C-Sci96.pdf http://courses.washington.edu/bangblue/Mojzsis-3.85Ga_Akilia..., but nothing to suggest it was diatomic in nature. Anyway. If their evidence isn't falsified, even if this isn't extrasolar panspermia, it's a demonstration that panspermia is possible.
    - marze 14y ago
      You're guessing the rock in question did fall from the sky, but that it was blasted of the Earth previously? Aren't there features of chontritic meteorites that would make it fairly easy to distinguish from an regular rock? Given the incomplete theories on how cellular life got a start, I don't see why people think evolving on Earth is any more likely than arriving from somewhere else. More time and more planets.
      - madaxe 14y ago
        Well, they appear to have decided it's a carbonaceous chondrite through visual examination alone - you can only really be sure by whacking it through a mass spectrometer and seeing what isotopes you've got. Either way, I think panspermia is perfectly possible, but the jury's out until this is independently verified.
        marze 14y ago
        Well, if the science community ever decides Wickramasinghe is right I'll laugh. It was interesting to read about diatoms: about 25% of all photosynthesis, more than all the rainforests location on "tree of life" is unclear: "Despite a number of studies to examine phylogeny, using one or several genes, the relationships of diatoms to other groups are still unclear and there is still a huge gap in our understanding of how and when diatoms acquired their unusual morphology and life-cycle characteristics. The diatoms have often been treated as a separate phylum, reflecting their unique features. Pascher (1914, 1921) suggested that the diatoms have features in common with the Chrysophyceae and Xanthophyceae and therefore placed these classes and the Bacillariophyceae in the phylum Chrysophyta. Ultrastructural and molecular sequence data have confirmed the general thrust of Pascher’s idea, placing the diatoms unambiguously among the heterokont protists (‘stramenopiles’) within the chromalveolates (Adl et al. 2005)." and Wickramasinghe has hypothesized interstellar dust might be diatoms(!): "there exists a close correspondence between the measured infrared properties of diatoms and the infrared spectrum of interstellar dust as observed in the Trapezium nebula and toward the galactic center source GC-IRS 7. Diatoms and bacteria also exhibit an absorbance peak near 2200 Å, which is found to agree with the observed ultraviolet absorbance properties of interstellar grains."