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This puts water on Mars into the time range where life was known to exist here on Earth. The Martian water that carved these rocks was around until 3.7 billion

This puts water on Mars into the time range where life was known to exist here on Earth. The Martian water that carved these rocks was around until 3.7 billion years ago, which is around the age of the oldest known geographic evidence of life on Earth. (Life likely existed before that, since very few rocks that old still exist.) That means that even if life did not evolve on Mars, it could conceivably have been thrown from Earth to Mars at a time when Mars had liquid water. We know that bacterial spores today can remain viable in space for very long periods of time, much longer than the time for (say) a rock blown off by an impact on Earth to reach Mars. This was always a possibility, but the possibility that that life could've landed in liquid water makes it a lot more likely, I would think.

knodi123 2y ago
how could bacteria survive the sheer energy involved in that initial impact? There's the famous story of the manhole cover in los alamos that was launched into orbit by an underground nuclear test- but in reality that manhole cover was turned into aerosolized iron. Ablation from air friction is proportional to both speed and air pressure. For an explosion to launch terrestrial rocks into space, the speed would have been highest at the surface where pressure is the highest. Yes, some meteoroids survive to fall to the earth's surface- but they decelerate gradually, starting up where the atmosphere is thinnest. And even then those get heat-sterilized, don't they?
- adrian_b 2y ago
  If the bacteria were deep inside a rock ejected by an impact on a planet, which then falls as a meteorite on the other planet (as it is known to have happened for some meteorites fallen on Earth, which had been ejected from Mars or from Moon), then bacterial spores could survive, even if the external layers of the original rock are vaporized by the heat, if the rock had been big enough, so that the inner part would not have reached a high temperature. The same happens with the astronauts coming back to Earth, who survive despite the external shield being vaporized by the heat. If a body has low thermal conductivity and high thermal capacity, the inner part will maintain a low enough temperature, even when the outer part is above boiling temperature. On Earth, one can find bacteria in some rocks that are not completely compact, but which have pores or crevices, through which the water and gases needed by bacteria can pass. Such events would be unlikely, but not impossible. In the early Solar System, when big impacts were very frequent, there must have been many cases of rocks traveling between close planets, in all directions. After the planets had reached their current structure, meteorites coming from either Mars or Moon to Earth have remained frequent, due to the lack of a thick atmosphere on Mars and Moon, combined with their weaker gravity, but meteorites going from Earth to any of them have become extremely unlikely, because most bodies colliding with the Earth do not reach its surface, and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower.
  - knodi123 2y ago
    > and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower. Ah, but the case I was replying to was about rocks making the trip back in the era when earth and mars both had enough atmosphere to support flowing liquid water.
- pyinstallwoes 2y ago
  Particles from Venus reach earth and visa versa quite often.
  - knodi123 2y ago
    yeah, but- dust and stray ions. nothing that could protect a bacteria from the extraordinary heat and energy of an explosion that launches it from the surface into space in a single titanic shove.
ChuckMcM 2y ago
At one point I started writing a speculative fiction story about Tardigrades who lived on Mars but became aware that climate change was going to threaten their existence so they created an ark on Mars, set it up to be launched by an asteroid impact and then went dormant until it landed on Earth.

knodi123 2y ago

how could bacteria survive the sheer energy involved in that initial impact? There's the famous story of the manhole cover in los alamos that was launched into orbit by an underground nuclear test- but in reality that manhole cover was turned into aerosolized iron. Ablation from air friction is proportional to both speed and air pressure. For an explosion to launch terrestrial rocks into space, the speed would have been highest at the surface where pressure is the highest. Yes, some meteoroids survive to fall to the earth's surface- but they decelerate gradually, starting up where the atmosphere is thinnest. And even then those get heat-sterilized, don't they?

adrian_b 2y ago
If the bacteria were deep inside a rock ejected by an impact on a planet, which then falls as a meteorite on the other planet (as it is known to have happened for some meteorites fallen on Earth, which had been ejected from Mars or from Moon), then bacterial spores could survive, even if the external layers of the original rock are vaporized by the heat, if the rock had been big enough, so that the inner part would not have reached a high temperature. The same happens with the astronauts coming back to Earth, who survive despite the external shield being vaporized by the heat. If a body has low thermal conductivity and high thermal capacity, the inner part will maintain a low enough temperature, even when the outer part is above boiling temperature. On Earth, one can find bacteria in some rocks that are not completely compact, but which have pores or crevices, through which the water and gases needed by bacteria can pass. Such events would be unlikely, but not impossible. In the early Solar System, when big impacts were very frequent, there must have been many cases of rocks traveling between close planets, in all directions. After the planets had reached their current structure, meteorites coming from either Mars or Moon to Earth have remained frequent, due to the lack of a thick atmosphere on Mars and Moon, combined with their weaker gravity, but meteorites going from Earth to any of them have become extremely unlikely, because most bodies colliding with the Earth do not reach its surface, and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower.
- knodi123 2y ago
  > and for the few that reach the surface the probability that an ejected rock could exit Earth's atmosphere is even lower. Ah, but the case I was replying to was about rocks making the trip back in the era when earth and mars both had enough atmosphere to support flowing liquid water.
pyinstallwoes 2y ago
Particles from Venus reach earth and visa versa quite often.
- knodi123 2y ago
  yeah, but- dust and stray ions. nothing that could protect a bacteria from the extraordinary heat and energy of an explosion that launches it from the surface into space in a single titanic shove.

ChuckMcM 2y ago

At one point I started writing a speculative fiction story about Tardigrades who lived on Mars but became aware that climate change was going to threaten their existence so they created an ark on Mars, set it up to be launched by an asteroid impact and then went dormant until it landed on Earth.