
Formation of the moon brought water to Earth - dnetesn
https://phys.org/news/2019-05-formation-moon-brought-earth.html
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kristianp
That doesn't bode well for the idea of habitable planets in other solar
systems. If this kind of collision is relatively rare, most rocky exo-planets
will have much less water than Earth has.

Reminds me of Asimov's storyline in the Foundation series about the rarity of
the planet that humans come from (and the reason no complex lifeforms existed
anywhere else), although his premise was a large amount of radioactivity on
earth, IIRC.

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dumbfoundded
We just don't know enough about life or planet formation to know how this
bodes.

On its surface, everything that makes the formation of the Earth appear rarer
would suggest life, in general, is rarer but honestly we don't know. We don't
even know if there's life on Europa even though there would appear to be all
the conditions present to make life as it lives at the bottom of our oceans.

We don't even know if water is a reasonable prerequisite for life. We don't
know if life has to be carbon-based. Sulfur also presents a reasonable
alternative. Would we even recognize other life if was right in front of us if
it relied on completely different mechanisms? Maybe even our idea of time is
too short lived or long lived to even recognize other complex systems as
alive.

We shouldn't extrapolate too much from a single data point.

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simonh
It simply isn't true that we're completely ignorant on these questions. We
know an awful lot about the chemistry of all the known elements and it's
pretty clear water and Carbon are by far the best candidates for supporting
complex, rich chemistries across a wide range of environmental conditions.

It's not that alternative life chemistries are necessarily impossible, but
equally it's plausible that they might well be non-viable above a very
primitive level at best. They would have many orders of magnitude fewer
options available to them for biochemical resources, pathways and molecular
geometries to take advantage of. Chemically speaking, not all elements are
created equal.

Take Sulphur for example. It's far more reactive than carbon, so chemically
unstable in many more environmental conditions. It generally only forms linear
chains, rather than the complex branching structures of carbon. It also bonds
with far fewer other elements in ways that are likely to be chemically useful.
If you have carbon available, Sulphur is a very poor substitute. It's high
reactivity might make it a passable alternative to Oxygen though.

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dumbfoundded
It sounds like you're paraphrasing the wiki page I attached in a different
comment:
[https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...](https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry)

To address your point, I would say we are extremely ignorant about what the
solution space of life looks like. Hydrothermal vents are a very recent
discovery. Before this discovery, it was unexpected that such complex and
large organisms could exist without light from the sun. As a planet, Earth is
teeming with life. Everywhere you look on Earth, you can find it. Even though
we have a good understanding of chemistry, we have little clue as to what's
important to form complex and self-propagating systems.

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RosanaAnaDana
I don't know if there are any astrobiologists or chemists, but this brings to
mind one of my favorite pet theories regarding abiogenesis, one that I've been
thinking of more and more since the new horizons mission.

When we did the flyby of Pluto, I was drop jawed when we saw how dynamic the
surface was. I sincerely expected a rockier, more oxidized, surface with no
clear evidence of a geological cycle. Obviously what we saw was far more
complex, and it brought the idea that a geology of volatile ices would be
possible on these more marginal bodies (like Pluto).

The question I have is regarding what kinds of chemistry are possible on icy
bodies like Pluto. If there is a complex geology, this indicates to me that
things are going from liquid to solid (nitrogen ice, oxygen ice, etc..), so
are some kinds of chemical bonds (specifically, organic ones) can form if a
body like Pluto is has a dynamic geology?

Is it possible that the organic precursors for life are constantly
accumulating on icy bodies like Pluto, and while obviously, live can't form on
Pluto, could an impact discharge a massive quantity of precursor chemistry
onto a planet more hospitable?

Its an interesting aside that pretty much imminently after the earths surface
solidified and cooled after the impact even, life began.

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dumbfoundded
Not an expert here at all but asteroids often do carry precursors for life.

Asteroids on Earth have been found carrying organic compounds:
[https://www.smithsonianmag.com/science-nature/the-
building-b...](https://www.smithsonianmag.com/science-nature/the-building-
blocks-of-life-may-have-come-from-outer-space-3884354/)

~~~
RosanaAnaDana
Sure, but my point here isn't about presence, but quantity. We've known that
radiation can cause the creation of bio-molecules and precursor molecules for
a very long time. But there almost no way that process can generate a
significant enough quantity of these molecules to really seed planets. Largely
its about concentration gradients, which is why I personal have found
arguments about life forming via early oceans unconvincing. A couple asteroids
(or even hundreds) worth of bio-molecules spread out over an ocean, is still
basically nothing. You have to have enough material concentrated in a small
enough space; you need a thermodynamic process that postpones equilibrium;
then you need a gradient to drive the formation of more and more complicated
molecules.

Like, Pluto type objects are far and away more common then earthlike objects.
If there is a process that can accumulate bio-molecules in mass on these types
of bodies, that's pretty game changing.

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njarboe
The scientific article that this summary is based on can be found here[1].

[1][http://dx.doi.org/10.1038/s41550-019-0779-y](http://dx.doi.org/10.1038/s41550-019-0779-y)

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mirimir
So is Theia's core now Mercury?

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dr_orpheus
The theory is that much of Theia was absorbed in to the Earth and the mass
that was ejected during the collision became the moon.

[https://en.wikipedia.org/wiki/Theia_(planet)](https://en.wikipedia.org/wiki/Theia_\(planet\))

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tigerlily
What would happen if we added (5 or 10%) more water to the Earth today?

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vertline3
I was just reading that Mars was found to have the remains of an icecap one
mile under the surface, so was Mars also hit with a meteor?

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DavidComposing
wait what?

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simonh
All the other inner planets and asteroids are dry, but Earth is wet, so it’s
always been a bit of a mystery where the water came from.

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encoderer
Where did the water on Mars come from? Any correlation?

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simonh
Mars, as far as we can tell, has very little water compared to Earth, even
back when it appears to have had liquid water on the surface. It's a bit
further out, so we'd expect it to have more water compared to the rest of the
inner planets. It seems to be consistent with occasional deliveries of water
from collisions with comets. In comparison, Earth has vastly more water.

