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To be clear: the LUCA is the last universal common ancestor. There was earlier life, before the LUCA; it's just that all its surviving descendants are also LUCA descendants.
This is important to know while reading the text, because it explains why the LUCA was so surprisingly complex.
Yes but, this was maybe 300 million years after Theia smashed the proto-earth half destroying the planet and forming the moon. The whole planet must have been sterilised by that right? So it’s pretty damn quick isn’t?
300 million years is still a lot of time, even evolutionarily speaking. For reference, it's ~twice the time between us and our last common ancestor with platypuses (160mya). Plus I kind of expect this sort of barely celular... being? structure? that gave origin to the LUCA to evolve way faster.
And more importantly, it means the LUCA wasn't the only one around those times. It was part of some sort of ecosystem already. Alongside a bunch of less lucky siblings.
it's ~twice the time between us and our last common ancestor with platypuses (160mya) That’s a good point and it really puts deep time in perspective. But it still points the no life / life transition being extremely easy? Doesn’t it? In two to three hundred myas we had a jump from barren hell scape to single cell life. That makes if look like life must be pretty easy to get started or am I missing something? Not a biologist so I suspect I’m missing something.
I'm not a biologist either, so take what I say with a grain of salt.
But it still points the no life / life transition being extremely easy? Doesn’t it?
Perhaps so, provided the conditions are suitable for that.
In special, going from free-floating to contained self-replicating junk seems to be a damn big leap, since the containment (aka membrane) needs to be selective: it needs to let some material to go in/out to allow replication and get rid of leftovers, but not enough to threat the integrity of the structure.
It was still most likely a hellscape for our standards, though. Just not a barren one.