The Mars panspermia theory mentioned in the original article simply moves the "randomness" to a primordial soup 83 million km away during the same time frame, and adds the exceptionally strong claim that Mars was so much more conducive to spontaneous formation of organisms capable of surviving on earth that it is more probable life emerged there and made an unexplained interplanetary journey than it emerged on the planet it currently [exclusively] lives on.

Considering the best evidence of Mars being conducive to earthly life formation is the likelihood of it more closely resembling earth's conditions in the past, it doesn't seem like the sort of claim likely to resolve issues with earthly primordial soup hypotheses...

That's untrue. See here https://www.scientificamerican.com/article/how-did-life-begi....

An "Earthlike" planet is required. Mars may have qualified at one point, but doesn't now.

An earthlike planet is require for earthlike life.

It is fallacious to assume other life couldn't be different -- we can't prove or disprove that. Likewise, we still don't know exactly how life started here; we simply have a few good theories.

I don't think we have "good" theories about how life started here. In particular, the complexity gap from abiotic chemicals to the smallest known organism capable of independent reproduction (about 4 billion atoms!) is extremely large, and no theory has done more than handwave about how that gap is to be crossed.

this is what has always annoyed me about basically every space movie ever made. even life a star away, let alone another galaxy away, is likely to be startlingly different from the oxygen-absorbing, ossified calcium-braced, protein-enriched, atp-powered water blobs with heads, legs, and feet we have on earth. and that's just the the biochemical stuff we're familiar with.

i think in the end it's going to come down to what you really consider "life" to be.

there is an implicit part of our definition that includes timescales and size, and this puts some limits on the type of chemistry that can be involved in order to qualify.

if you open up the definition to be things that work on totally different timescales and sizes than we consider, then i think its fair to say that the chemistry doesn't need to be similar at all.

but for things that form blobs of life on the rough range of scales found on earth, and that "do stuff" in the range of timescales that we see on earth, there are not too many choices. silicon often gets touted as an alternative because of its ability to form branched structures. do you know of any other ideas?

sure, chemistry has a somewhat limited palette to work with, but life happens in the gap between potential and kinetic, between hot and cold, between proton and electron. that's a tiny space but a huge gap.

dna is mostly a 4-note tune, and computers, the potential precursor to artificial life, 2. i'm sure something as vast as the universe can come up with a little more variation than skin type in those tiny little gaps.

I don't believe that we'd recognize computer-ish artificial life as life in the sense that we're discussing here.

ps. I have my Artificial Life III conference t-shirt from 1994 :)

> atp-powered

I think GTP-powered file is possible, even the glucose metabolism produce one GTP (and many ATP). (Perhaps I'm missing something, Chemistry is not my main specialty). Perhaps it is even possible to have NADH-powered life, but it is more different so it may be impossible.

> ossified calcium-braced

Diatoms use silica, insects have a protein exoskeleton, and octopus are weird.

> oxygen-absorbing, [...] protein-enriched, [...] water blobs

I guess these three are safe bets (with a little different selection of amino acids).

Oxygen absorbing isn't necessary, of course. Life on earth got along without it for a while until those darned cyanobacteria starting poisoning everyone else.

Eukaryote life did not appear until after the Oxygen Catastrophe though.

That's true, but how much earlier might it have occurred if the oxygen catastrophe had not occurred and caused a mass extinction? Hard to say...

Due to convergent evolution [1], I'm not sure life that originated on an Earth-like planet would look completely different from Earth life, at least on a macroscopic level.

[1]: https://en.wikipedia.org/wiki/Convergent_evolution

that's predicated on the same conditions as life on earth. a universe can surely come up with some more variety.

My point is that I think convergent evolution would be likely to produce “water blobs with heads, legs, and feet” on other Earth-like planets, i.e. planets with lots of liquid water and lots of solid land.

If you’re thinking of planets that are not similar to Earth, of course all bets are off.

What bothers me about every space movie made is that all those planets have life on them (or, worse, intelligent life). Fermi says hi.

Fermi can blast out "Hi" with a 100GW of power and he is unlikely to be heard in Andromeda, which for all we know could be teeming with life and host to something like an Iain Banks Culture series space opera.

We know that fewer than about 1 in 100,000 galaxies has a Kardashev Type III civilization. So the Fermi argument has some bite even at cosmological distances.

But anyway, this was about SF movies where our heroes visit Arglebarg IV and have adventures with the natives. It's like Victorian adventure stories transplanted into space without bothering to think things through. Let's kill our dysfunctional tropes.

> We know that fewer than about 1 in 100,000 galaxies has a Kardashev Type III civilization.

But we.. don't? We just don't have anything to compare to.

A K3 civilization is one that has diverted a significant fraction of the stellar output of a galaxy to its own uses. They have to dump their waste heat somehow, and that's visible in the far to mid infrared. So we can compare the IR emission of galaxies to look for oddballs with a lot of IR.

https://www.centauri-dreams.org/2015/04/16/g-hat-searching-f...

“Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes. That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them.”

When we assume K3 capabilities, why don't we assume they dump their waste emissions away into something like (artificial even?) black holes? Maybe they are shy and afraid of the intergalactic "Dark Forest"? ( https://en.wikipedia.org/wiki/The_Dark_Forest )

The basic problem with that idea is black holes are too small. The amount of low temperature radiation that one could dump into them would be insufficient.

I think the point is that if a large number of galaxies had Type III civilizations, we would notice, because the definition is that they use most of the available energy in their galaxy making the galaxy radiate more infrared than visible light. But that doesn’t mean life isn’t common, it may just mean that a Type III civilization is either physically impossible or very unlikely.

That's also discussed in the article. The author states that Mars may have qualified before Earth did.

Edit: Also, the article you linked specifically states "Scientists debate a range of ideas about how life on earth began", undermining your first point.

I think the opposite conclusion is true: we know nothing about how life gets started, we know life exists on Earth, we have seen no evidence of life anywhere else, so the reasonable assumption is that life started on Earth.

One thing we know (almost) for sure is that no new forms of life have emerged on Earth for hundreds of millions of years. So we should expect that the conditions required are quite special indeed, or the event is extraordinarily unlikely. As such, it is silly to assume that any other planet is "similar to Earth" in the ways that matter for life appearing based on simplistic observations (temperature, distance from the sun, existence of the most basic required elements).

Do plants count? Then I have cacti for you, which are thought to be only a few dozen million years old.

I am referring to abiogenesis - life arising from non-life matter. Cacti have not appeared out of simple chemicals, they have evolved from other plant-based lifeforms (in fact, there is no "first cactus").

My point is that, despite the huge abundance of life on Earth today, it is all based on a very old abiogenesis event, with all indications that it was more or less a singular event.

All life on earth seems to be part of the same philogenetic tree, so it seems that life appeared once and then kept evolving from that initial life-form. Of course, there is a good chance that there was some variety of initial organisms that either merged together in symbiotic relationships, such as mitochondria with the rest of the cell, or got out-competed by the one type of organism that we are all descended from. This still indicates that life arose in a single place and only over a relatively short amount of time.

Hm. OK. thx.

>Martian surface temperatures vary from lows of about −143 °C (−225 °F) at the winter polar caps[14] to highs of up to 35 °C (95 °F) in equatorial summer.

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

Had to look this up. Seems like there is the same temperature window available on Mars that is needed for life on earth.

That’s today without atmosphere, liquid water and with a solidified core I’m not sure were close to estimating when the core has solidified as far as I know we also have no method for dating anything on mars.

When mars was wet, geologically a GI d and still had an atmosphere the temperatures would’ve been much closer to earth today.