4 ms·

Allen Hills Mars Meteorite: 20 Years Later, Debate Continues

33 points by jostmey 9y ago

dmix 9y ago
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?
- adrianN 9y ago
  Are the rovers even equipped with anything that could detect microscopic magnetite string-of-pearl formations?
  - tabtab 9y ago
    I think they meant the rock spurred general interest in further exploration, not just magnetite research.
Radim 9y ago
"…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?
- jessriedel 9y ago
  There are sharp phase transitions between different phases of matter. It's a difference in kind, but it's all made out of atoms.
  - eesmith 9y ago
    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."
    - jessriedel 9y ago
      I'm well aware of this and it doesn't change my point.
      - eesmith 9y ago
        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?
        jessriedel 9y ago
        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.
        eesmith 9y ago
        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_defining_%22life%22 https://en.wikipedia.org/wiki/Mimivirus#Implications_for_def... 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 .

33 points by jostmey 9y ago

dmix 9y ago

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?

adrianN 9y ago
Are the rovers even equipped with anything that could detect microscopic magnetite string-of-pearl formations?
- tabtab 9y ago
  I think they meant the rock spurred general interest in further exploration, not just magnetite research.

Radim 9y ago

"…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?

jessriedel 9y ago
There are sharp phase transitions between different phases of matter. It's a difference in kind, but it's all made out of atoms.
- eesmith 9y ago
  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."
  - jessriedel 9y ago
    I'm well aware of this and it doesn't change my point.
    - eesmith 9y ago
      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?
      - jessriedel 9y ago
        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.
        eesmith 9y ago
        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_defining_%22life%22 https://en.wikipedia.org/wiki/Mimivirus#Implications_for_def... 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 .