There's a huge difference between what evolved organisms can adapt to, and the conditions necessary to start life.

Look, humans already adapted to being in space for prolonged periods of time. We adapted to every climate. But drop a naked human in a random spot on our planet, and he will die with high degree of probability. And that's after billions of years of evolution.

Out of which some 3 billion years had to pass before unicellular forms of life evolved into multicellulars.

Who knows if this jump alone should be taken for granted - plus, not many planets could provide 3 billion years of "good weather" (or staying habitable) to start with.

> Out of which some 3 billion years had to pass before unicellular forms of life evolved into multicellulars.

We might be a slow developer and poor representative sample in that respect, but without more data it's hard to tell.

> plus, not many planets could provide 3 billion years of "good weather" (or staying habitable) to start with.

I suspect the opposite will be true, red dwarfs are the most common type of star and are stable for trillions of years. Even if the average time it took multi cellular life was 30 or 300 billions years then it might not matter for life evolving there. They do come with some other caveats though: https://en.wikipedia.org/wiki/Red_dwarf#Habitability

That is the odd thing about the history of life on Earth isn't it? Prokaryote popped up almost as soon as was conceivably possible. And then. Nothing. For billions of years. The plausible explanation is that you need Oxygen for Eukaryotes and that's how long it to change the chemistry of a planet. It just seems weird to me.

"Let me make my position clear. The miracle, and I do not mean it in the religion sense, I mean it in the evolutionary sense, the miracle of the evolution, is the cell. While there are theories involving an RNA world and selforganising, it remains a mystery. Once you had the eukaryotic cell from the point of view of evolution and development it was downhill all the way, very very easy. "

Lewis Wolpert : https://link.springer.com/chapter/10.1007/978-3-0348-8026-8_...

Just a reminder - we were naked for most of our history and were able to survive.

But not in nearly as many emvironments as we can today. We can assume, over time, life learns to live under absurd conditions; but its hardly safe to think it can start in those same conditions.

I think humans are a bad example - we use our own relatively highly developed intelligence to solve problems, and that means we had to feel safe enough from the environment long enough to develop that. But if we look at older organisms, like the tardigrade, there are some incredibly robust creatures out there.

However, all the life we know of is part of the same Earth system. Just because some extremophile exists in a freezing desert or boiling pool does not necessarily mean that the same environments on other planets would have those organisms.

Life on Earth evolved and spread under specific conditions - our gravity, sun brightness, geology, magnetic field, large moon, etc etc. It then spread to all possible environments on the planet and evolved to live there.

Unfortunately, it could be that the 'growth conditions' for life are quite specific even if - once it gets going - life can evolve to more general environments.

> Even the lifeforms that we do know of, occupy a very broad spectrum in all metrics, existing at all sorts of extremes.

But all lifeforms we know evolved from one common ancestor, it's one tree of life. As far as we know life evolved here only once.

So we know that once life happens it can become completely ubiquitous, but it doesn't say anything about that crucial first step.

> But all lifeforms

That's not nessisarily true. Single celled organisms have a rather fluid exchange of genetic information even our 'single cells' are really several different organisms. It's possible life evolved many times on earth and current single celled organisms and thus all life has a mismatch of ancestors.

Further, life may regularly evolve even today, but simply get eaten due to the stiff competition.

PS: We know life evolved at least once, but the high end could be multiple times a second on earth.

> It's possible life evolved many times on earth

It's also possible it evolved elsewhere and rode here on a meteor - or was brought here by some other lifeform several orders of magnitude more advanced than us, using earth as their own cosmic terrarium.

Why not both. We could also be descendants of an invasive alien species that killed off all of Earth's native lifeforms.

It's good practice to assume the simplest possible solution. However, the full range of the full range of what might have happened is ridiculously large.