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Comment by perihelions | Hacker News Reader

Question for people up to date with modern biochemistry: if there were extraterrestrial microbes on Earth right now, with totally unique chemical origins unrelated to proteins, nucleic acids, saccharides, etc., how likely would we be to notice them? And which analytic method would find them first?

Is there a systemic search for this kind of crazy stuff, and where are the review papers for them? I don't know the keywords!

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Very, very unlikely like astronomically so. Most microorganisms are so small they're practically transparent so we have to exploit biochemistry to "stain" them - hence why you'll often hear of bacteria classified as either Gram positive or negative, because of the Gram stain. If the biochemistry is unique or even slightly different i.e. right handed chirality, we'd basically have zero of our usual tools at our disposal.

There's already a whole world of terrestrial microbes that we expect or even know for certain to exist but can't culture, let alone stain, which means we can't really study them. We'd (theoretically) eventually notice them on electron microscopy slides though, which is how we know there's many unculturable microbes, but whether we'd recognize them as alien is a completely different matter. The microbial world is very diverse and there's nothing I can think of that'd set something apart as alien since we can analyze the chemistry with an electron microscope.

There's already a whole world of terrestrial microbes that we expect or even know for certain to exist but can't culture, let alone stain, which means we can't really study them.

I'm going to bookmark this for the case someone asks: what piece of information that seems basic did you ignore until very recently?

A question that often arises is: if current life evolved from chemistry that's simpler than DNA, why has that one disappeared? Maybe it hasn't.

> A question that often arises is: if current life evolved from chemistry that's simpler than DNA, why has that one disappeared? Maybe it hasn't.

If that's the case, it was almost certainly because of the atmospheric oxygen.

Almost all of the chemical reactions that used to happen before it do not happen anymore on the wild.

Having oxygen in the atmosphere and liquid water truly steers the kinds of chemistry we study.

> A question that often arises is: if current life evolved from chemistry that's simpler than DNA, why has that one disappeared? Maybe it hasn't.

Probably for the same reason we don't see relay or valve based digital computers anymore. They were outcompeted to extinction by their more sophisticated descendants.

> A question that often arises is: if current life evolved from chemistry that's simpler than DNA, why has that one disappeared? Maybe it hasn't.

The general thinking is that DNA evolved from RNA, which has certainly not dissappeared.

As to pre RNA chemistry, there is a good chance that the relevent chemicals still exist and are well studied. The issue is more that we have not worked out the specific proccess that led to the development of abundant RNA.

> There's already a whole world of terrestrial microbes that we expect or even know for certain to exist but can't culture, let alone stain, which means we can't really study them.

That sounds pretty cool for a hobbyist to potentially spend time on. Anything you could recommend to look at, for following up on this unknown stuff?

Not at all familiar with biochemistry but octopuses are aliens on earth with very different evolutionary track having developed ‘brains’ before our ancestors did independently! It’s crazy we don’t study things like cephalopods like we do SETI etc…

When ever people talk about terraforming planets I just think they sound insane. Like we don't know how a majority of our own planet even works yet you think we can recreate it?

If someone told me that we know more about space then our own oceans I wouldn't be surprised.

it's not an either-or. we can do both, in fact we should do both.

> octopuses are aliens on earth with very different evolutionary track having developed ‘brains’ before our ancestors did independently

IIRC octopuses appeared in the Jurassic era by which time 'brains' were well established amongst our ancestors, notably the earliest proto-mammals.

I agree that they are an interesting form of alternative intelligence and parallel evolution, but biochemically they have numerous things in common with us, including many gene systems that are highly conserved across a variety of different clades, including our own.

"Shadow biosphere" may be a useful search term.

Searching this term I found an article with an amusingly similar title:

> Life on Earth... but not as we know it

https://www.theguardian.com/science/2013/apr/14/shadow-biosp...

We didn't even know about Megaviruses[0] until 2010.

[0] https://en.wikipedia.org/wiki/Megavirus

Or Pandoraviruses[1] in 2013.

Also TIL giant viruses have their own Stargates[2].

[1] https://en.m.wikipedia.org/wiki/Pandoravirus

[2] https://www.livescience.com/triggers-for-giant-virus-infecti...

If found, how could we even be sure that their origin was extra terrestrial?

We're not really looking for microbes.

Sure, they can still be very interesting from the bio/chemistry point of view. But it's the advanced civilizations that we're really after.

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