Organic molecules discovered by Curiosity consistent with early life on Mars | Hacker News Reader

Organic molecules discovered by Curiosity consistent with early life on Mars

phys.org

73 pointslelf28 comments

The article touches on this a bit, but I've always wondered what is defined as life. As noted in this article, source of complex organic compounds on Earth is most likely biological, but on other planets, the odds are pretty low for that. If life is self sustaining complex organics, then I guess the bar is pretty low to find it in the universe.

However, if life is defined as adapting complex organics(evolution), where the errors in replication of cells triggers different combinations then it gets more interesting as that is in a nutshell how life started evolving on Earth.

Whatever definition we end up with, if it requires organic molecules from principle, it's too strict to be useful, and if does not require evolution it's way too broad for anything useful.

Is evolution real a prerequisite for life or is it just a consequence of imperfect replication of DNA? The fact that mutations can be beneficial and accumulate in a population seems more like a happy accident, rather than a fundamental part of life. But then again, I'm no biologist.

It's important to note that definitions don't reflect reality so much as humans' interpretations of it.

IMHO, the life/not-life dichotomy is a false one. We observe the "lifecycle" on our own timescales, which biases our understanding of what is "living" and "not living" as distinct entities. For instance: is the planet Earth "alive"? Are geological processes synonymous with "life"?

Further, what are "organics"? If we take the biochemists' view, it's anything in which organic molecules occur. Are rocks then "alive" since they fit into this definition?

In biology 101, they taught us that life is something with the following properties:

1. Has order

2. Has metabolism

3. Has evolutionary adaptation

4. Responds to the environment

5. Reproduces

6. Grows and develops

Which seems fine as a definition, but certain physical processes are still a little ambiguous. Like consciousness, there's probably not a clear dividing line between life and non-life, but rather a gradient between the two.

Why is evolutionary adaptation a necessity? If some reasonably complex organism evolved and then perfected its DNA replication to the point where no mutations occurred, and thus it could not evolve any further, it would cease to be considered alive?

Just because no mutations are occuring doesn't mean natural selection isn't taking place, it just means that there are no fitter variants in that organism's immediate fitness landscape

If we find life a second time in our solar system, would that imply that life throughout the universe is much more likely to be abudant? Answers to the fermi paradox I've heard is that there may be some unknown true difficulty for creating life. A second form of life in our solar system would counteract that belief?

If true, then I'd be worried about some Great Filter ahead of us (ie technology destroying us) as that may be a plausible reason why we haven't spotted aliens yet?

Not necessarily. Impacts have ejected material that ended up on the other of Mars and Earth. Life might have travelled on it and thereby life on both planets could have a common ancestor.

https://en.wikipedia.org/wiki/Martian_meteorite

It's worth pointing out that this _should_ probably increase your estimate from the Drake equation slightly. It means that even if organic 'early life' compounds can arise on planets that nevertheless aren't suited to more complex life, they could still spread to planets that _are_ suited, but don't necessarily have those compounds yet.

If that life has DNA/RNA, it doesn't say much about the Fermi paradox. If it has a totally different basis, it's a huge data point.

Hopefully you're already worried about that.

If we find organisms on Mars, we need to first prove they belong to a separate tree of life. It's known that asteroids like the one that killed the dinosaurs could have seeded planets and moons across the solar system.

If life existed on Mars then to me that strongly implies that there is some Great Filter in our past that we did pass but Martians did not

multicellular life

Multicellular life is easy, it has evolved independently more than 25 time on Earth https://en.wikipedia.org/wiki/Multicellular_organism

I think that the step from Prokaryote to Eukaryote is much more difficult. (Feel free to disagree. Nobody is sure.)

[Assuming there was an ocean in Mars, and assuming there was life.] The problem is that the ocean disappeared, probably due to geological reasons that neither a unicelular or multicelular lifeform can solve. Sometimes you are just born in the wrong planet. https://en.wikipedia.org/wiki/Mars_ocean_hypothesis

Moreover, it's probably easier for an unicelular bacteria-like or archaea-like lifeform to survive. Some of the one from Earth can extract energy from some rocks or volcanic fumes, so they can survive in weird places.

Edit: Fixed "Eukaryote to Prokaryote" -> "Prokaryote to Eukaryote"

> the step from Eukaryote to Prokaryote

I think you mean from Prokaryote to Eukaryote?

Thanks! Fixed.

We know the step from "pro" to "eu" is hard, in circumstances like young Earth, just from how long it took to happen. But other planets will have other circumstances.

> I think that the step from Prokaryote to Eukaryote is much more difficult. (Feel free to disagree. Nobody is sure.)

Do you (or others) recommend any books exploring these conditions of life? The biology course I took online dabbled in explaining the difficulty of biological existence but wasn't the purpose.

I suspect that intelligent-like-us life is vanishingly rare. It’s only happened to one species (maybe a few of our extinct relatives) out of billions of species on Earth so far. And even we spent most of our history not being space-faring — it doesn’t feel inevitable even given our biology that we would be.

and if we were wiped out early on then Earth would most likely continue on how it was for the previous hundred million years with megafauna and life branching out in similar niches it has gone before.

idle speculation: maybe there's an uncanny valley type effect where intelligent tool users are inherently hostile towards their near peer species? could explain why our ancestors are extinct but much less capable primates still exist.

if true, the number of such species might converge to one over time.

Well, predisposition to tribalism may be the manifestation of a strong evolutionary pressure against those early hominids who did not eliminate other subspecies with prejudice.

Two examples of primitive life, with water nearly everywhere we look, and yet with only one reaching civilization, and no examples of interstellar life (though we have created interstellar space ships!) to me implies ...

That the great filter is behind us. I expect primitive life to be common, and civilizations to be rare.

Or rather, the "great filter" is a series of probabilistic challenges which each instance of life either fails (regresses / stagnates) or overcomes, along with probabilistic events that jump things forward to the next "stage". If not for an asteroid long ago, dinosaurs would still rule the earth, perhaps.

I personally believe there are four great-filters. We're moving through the 3rd, with no solution for the 4th:

1. Water bearing & warm planet.

2. Plenty of time for eukaryotic cells to develop.

3. Intelligent life doesn't destroy itself (by whatever means), and is not destroyed by highly unlikely events.

4. Heat death of the universe.

It’s probably too optimistic to assume that there is a single “great filter”. Instead, there are probably a series of filters, any one of which could end a line that leads to an intelligent civilization that can reach into space.

Think of them more as achievement levels in a video game. You might die on this level, but if you don’t and get to the next level, you have to avoid dying on that level, now.

There are at least two solutions to the Fermi paradox, presuming widespread life. Each suffices, by itself, but both (and others) could be true, too. I.e., there need be no Great Filter; there could as well be hundreds.

First: if expansionist societies reliably destroy one another sometime after contact, remaining societies are not expansionist, and so (therefore) do not make contact. Expansionist societies that make contact and do not destroy one another continue expanding until they encounter another, and the dice are rolled again.

Second: if societies sufficiently advanced to make contact first master controlled-fusion tech, then goldilocks planets become uninteresting. Look for aliens near Kuiper Belt objects where useful molecules are in piles conveniently frozen to the bottoms of shallow gravity wells. In this scenario, planets like ours are used only by extreme primitives. The aliens already know we have nothing interesting to say to them.

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