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"Life" may be the simplest hypothesis. Not clear its obvious which side of "Is there life on Mars?" is the extraordinary claim.

tsimionescu 6y ago
No, it's very clear that life on Mars is the extraordinary claim. We don't know of any abiotic structure that would be even half as complex as bacteria, and multicellular life is an absurdly complex possibility to take as 'the simpler one'
- JoeAltmaier 6y ago
  Not arguing for parallel evolution in this one. There are pieces of Mars on Earth. Possibly there are pieces of Earth on Mars. If they didn't contain spores, that would be unusual. So if its possible for fungi to grow in a Mars environment, it seems the more likely outcome. That's the question - can they grow there? Then, they are likely growing there.
  - tsimionescu 6y ago
    There is no reason to expect life to survive an asteroid impact. The sheer force would likely be enough to crush delicate cells, and the heat of the impact would likely sterilize any remnants. Also, there are no fungi living off frozen water at -50 to -70 C or below on Earth, and an asteroid impact doesn't really provide time for evolution to work its magic. Perhaps extremeophiles could be found that would survive, though even that is shaky without some form of liquid water, and they would be extremely unlikely to evolve to something approaching fungi (remeber that extremeophiles are prokaryotes, while fungi are eukaryotes, and as far as we can tell eukaryotes arose from prokaryotes only once in the history of life on Earth, so it was literally a once in 2 billion years event). Edit to add: Mars' surface is also extremely toxic to essentially all Earth-based life. Overall, it is very hard to imagine that any form of Earth-based life would have survived the series of events you suggest: an asteroid impact with Earth which propelled a chunk of rock to space, being exposed to space, then burning through the Martian atmosphere, crashing into Mars, then encountering the extreme cold, low pressure, missing oxygen and CO2, high radiation, the toxic soil of Mars, and not just surviving, but growing and thriving from this.
    - SubiculumCode 6y ago
      No. Not no reason. Science: https://www.sciencedaily.com/releases/2013/09/130912092731.htm https://www.sciencedaily.com/releases/2013/09/130912092731.h... A portion may well survive.
      - tsimionescu 6y ago
        Thank you for the study, I was surprised to find that (though I will note that it seems the impact speed on Mars can be larger than on Earth, depending on the size of chunk - I found antoher study that gave an upper bound of 8.52 km/s for large meteors with mass > 10^10 kg).

tsimionescu 6y ago

No, it's very clear that life on Mars is the extraordinary claim. We don't know of any abiotic structure that would be even half as complex as bacteria, and multicellular life is an absurdly complex possibility to take as 'the simpler one'

JoeAltmaier 6y ago
Not arguing for parallel evolution in this one. There are pieces of Mars on Earth. Possibly there are pieces of Earth on Mars. If they didn't contain spores, that would be unusual. So if its possible for fungi to grow in a Mars environment, it seems the more likely outcome. That's the question - can they grow there? Then, they are likely growing there.
- tsimionescu 6y ago
  There is no reason to expect life to survive an asteroid impact. The sheer force would likely be enough to crush delicate cells, and the heat of the impact would likely sterilize any remnants. Also, there are no fungi living off frozen water at -50 to -70 C or below on Earth, and an asteroid impact doesn't really provide time for evolution to work its magic. Perhaps extremeophiles could be found that would survive, though even that is shaky without some form of liquid water, and they would be extremely unlikely to evolve to something approaching fungi (remeber that extremeophiles are prokaryotes, while fungi are eukaryotes, and as far as we can tell eukaryotes arose from prokaryotes only once in the history of life on Earth, so it was literally a once in 2 billion years event). Edit to add: Mars' surface is also extremely toxic to essentially all Earth-based life. Overall, it is very hard to imagine that any form of Earth-based life would have survived the series of events you suggest: an asteroid impact with Earth which propelled a chunk of rock to space, being exposed to space, then burning through the Martian atmosphere, crashing into Mars, then encountering the extreme cold, low pressure, missing oxygen and CO2, high radiation, the toxic soil of Mars, and not just surviving, but growing and thriving from this.
  - SubiculumCode 6y ago
    No. Not no reason. Science: https://www.sciencedaily.com/releases/2013/09/130912092731.htm https://www.sciencedaily.com/releases/2013/09/130912092731.h... A portion may well survive.
    - tsimionescu 6y ago
      Thank you for the study, I was surprised to find that (though I will note that it seems the impact speed on Mars can be larger than on Earth, depending on the size of chunk - I found antoher study that gave an upper bound of 8.52 km/s for large meteors with mass > 10^10 kg).