
The Resilience of Life to Astrophysical Events - sndean
https://www.nature.com/articles/s41598-017-05796-x
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dandare
>... analysing the most resilient of species–tardigrades.

You don't need to kill the tardigrade if all its food is already long dead.

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13of40
The question is just whether it can eat dead things...

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VLM
When I read the article in depth, that was basically the plot line of the
article, that there is no reasonable astrophysics way to kill off deep ocean
vent life therefore they'll always be something to eat. There are some minor
mistakes in the article that don't significantly affect the conclusion, such
as thinking the boiling point of water at "bottom of the ocean" pressure
remains 100C, not in my thermodynamics steam tables...

It has certain implications relating to the odds of lower level life on other
planets. Even if nothing is living on Mars today, it seems almost certain
there's fossilized dead bodies up there. Possibly this is good news WRT soils
and future cultivation.

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amelius
OTOH, if life is resilient to many types of astrophysical event, then this
also increases the probability that we've already contaminated Mars with life
from Earth.

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jerf
If it is _that_ easy, nature beat us to it literally billions of years ago:
[https://en.wikipedia.org/wiki/Panspermia#Lithopanspermia](https://en.wikipedia.org/wiki/Panspermia#Lithopanspermia)
Googling the term "lithopanspermia" can also turn up further interesting
discussion.

It is good to try our best to sterilize our probes, because our relatively
gentle launch and landing and relatively quick transit may enable a lot of
things to survive the journey that otherwise couldn't. But there is a point
where it stops mattering, because despite what you may think, Earth and Mars
are already not fully isolated from each other, so sterilizing beyond that
point doesn't change much.

One of the exotic possibilities for "how easy is life to start" is that it
could still be very hard, _but_ we could find life on Mars and perhaps even
throughout the Solar System. But further examination might show that it all
sourced from one location. (Which may or may not be Earth in the first place.)
So there could be a period of excitement where it looks like life is really
easy, only for it to turn out that the evidence remains a sample of one even
so.

(The most likely way we'd make that determination is that there are certain
choices in our biology that are extremely highly conserved, but at the same
time, seem arbitrary. For instance, the mapping of what codons map to which
amino acids. While there is some fiddling around the edges (as there are
several more codons than there are amino acids), the core mappings are highly
conserved. If Martian life is based on DNA and has the same core mappings, it
probably comes from the same source as Earth life. Another example is protein
handedness preferences, though that's stronger in the other direction; a
biology with the other handedness would _not_ come from the same source.)

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amelius
This makes me wonder: people say that any goldilocks planet has a high
probability of showing life; but why then don't we see different variations of
handedness of molecules in Earth's life forms? (or variations in codon
mappings)

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jerf
One hypothesis is that a given planet will have one dominant line that will
squash the competition, so it's hard to witness multiple lines even if they
existed at one point. There are possible "winner take all" elements; for
instance, if a planet has two lines of life that each prefer the opposite
handedness, it is likely that over time one of them will "win", as the (say)
left-handed biosphere generates more left-handed proteins, which are poison to
the right-hand biosphere, resulting in eventually there being one dominant
biochemistry even if you seed it from the beginning with multiple.

It is also possible that life is, say, "medium" possible, and over the course
of the Milky Way's life could be expected to arise a few dozen times and
spread via panspermia, but in any given area only one of these may seed us,
meaning that while there is variation in life, we can't witness it without
traveling a long way.

Another possibility has been proposed that as our detection tools tend to
assume DNA, and we look for DNA when "detecting life", that if there _was_
some extremophile bacteria a couple of miles deep in the crust that truly was
from another line of succession that didn't use DNA, or used it in a way
unrecognizable to our equipment, that we could indeed even have run samples of
such life through our labs and simply not know it.

