
Allen Hills Mars Meteorite: 20 Years Later, Debate Continues - jostmey
https://www.space.com/33690-allen-hills-mars-meteorite-alien-life-20-years.html?20
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Radim
_" …we really do not have a good working definition of what constitutes life.
At the most fundamental level, we still do not know whether the difference
between animate and inanimate is simply a difference in kind or degree."_

What would a "difference in kind" look like?

I thought it was pretty well established at this point there's no magic, that
"life" is just another layer in the layers of natural complexity, how matter
organizes itself, from physics to chemistry to biology to sociology and
ecology.

Why would there be an expectation of a sharp (non-linguistic) boundary between
"life" and "non-life", animate and inanimate, physics and chemistry, chemistry
and biology?

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jessriedel
There are sharp phase transitions between different phases of matter. It's a
difference in kind, but it's all made out of atoms.

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eesmith
Except when there isn't.
[https://en.wikipedia.org/wiki/Critical_point_(thermodynamics...](https://en.wikipedia.org/wiki/Critical_point_\(thermodynamics\))

> "Above the critical point there exists a state of matter that is
> continuously connected with (can be transformed without phase transition
> into) both the liquid and the gaseous state. It is called supercritical
> fluid."

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jessriedel
I'm well aware of this and it doesn't change my point.

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eesmith
Which is that we should expect a sharp transition between life and not-life
because there are sharp transitions between some phases?

I don't see how that fits. Even if you think of "life" as a phase transition,
why does it have to be a sharp transition?

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jessriedel
It doesn't have to be. I'm just rebutting Radim's suggestion that since living
things and non-living things are both made out of atoms we should expect that
the difference between living and non-living is only of degree rather than
kind.

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eesmith
The phrase was "Why would there be an expectation of a sharp ..."

I agree - why would we expect a sharp transition?

When a radioactive particle decays, it too is a sharp transition. (By which I
mean the time scale is very short. At sufficiently fine resolution, it's hard
to tell exactly when an atom of element X becomes something other than an atom
of element X.)

That there are examples of very fast transformation doesn't mean that Radim is
incorrect in asking why we would expect the difference between life and non-
life to be one of those sharp transitions.

In a tabula rasa sense, it might be a good cautionary reminder to consider
exceptions like what you pointed out. But it's "pretty well established" (to
quote Radim) that the boundary between life and non-life is not distinct. The
standard question is, are viruses alive? The usual answer is "no", but
[https://en.wikipedia.org/wiki/Mimivirus#Implications_for_def...](https://en.wikipedia.org/wiki/Mimivirus#Implications_for_defining_%22life%22)
pushes it close to yes.

Humans have created an organism with a synthetic genome. Give another decade
or two and biologists will be creating semi-alive forms to explore what the
boundary means.

Further, there are definitions beyond the strictly biological one:
[https://en.wikipedia.org/wiki/Life#Definitions](https://en.wikipedia.org/wiki/Life#Definitions)
.

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jessriedel
> it might be a good cautionary reminder to consider exceptions like what you
> pointed out.

It's not just a single exception, it's a huge class of counterexamples which
is the focus of study for much of the field of condensed matter physics.

~~~
eesmith
And there is an much larger class of examples.

------
dmix
The scientist stated this fact:

> Magnetite crystals from Mars might more persuasively indicate life if
> they're found in string-of-pearl formations, as they are when created by
> bacteria on Earth, Chris McKay said. "If we find these chains on Mars, it
> would be compelling evidence of past magnetotatic bacteria," he said.
> However, so far researchers have not detected such strings, he added.

And later in the article it goes on to say:

> "The Mars Exploration Rovers, Mars Reconnaissance Orbiter, Phoenix lander,
> Curiosity rover, Mars Express mission with its Beagle 2 Mars lander — all
> can be traced to the ALH 84001 research.

So they have not been able to find any other examples of magnetite? I'm
curious why not? Is it something that will be rare if it does exist? Or given
that the original sample was billions of years old that any surface level
digging by a rover would likely have eroded it away?

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adrianN
Are the rovers even equipped with anything that could detect microscopic
magnetite string-of-pearl formations?

~~~
tabtab
I think they meant the rock spurred _general_ interest in further exploration,
not just magnetite research.

