Start with a simple organic or inorganic "oily" membrane surrounding some liquid water. (I believe you can produce this mechanically by shaking up oil & water, as an example.

Or

Water spheres held together by surface tension, absorbing outside materials via osmotic physics that begin to accrete or stick together.


What you can get are particles that look suspiciously like rudimentary cells. Maybe incorporate naturally occurring organic molecules at this time. (Such a concoction would probably be capable of incorporating just about anything.) Add in some mechanism for simple division: ie: when it gets too big and unstable, it cleaves off. (Others more qualified could comment here.)

And the real important part: give it a half billion years for billions upon billions of these things to slowly add in structure changes spanning every physical possibility. These spheres would be great little test tubes for natural laboratory experiments. Shear numbers and time would ensure that some are going to be more and more interesting from the point of view of efficient replication and ever-increasing interior complexity. There's no "come together" involved.

With so much activity going on, it's a sure bet not all these cells are going to develop identically. And at some point there would be a synergistic, symbiotic, reproductive advantage for some of these differing cells being stuck together.

I just realized that this is similar to the way I approach digital photography. Take zillions of shots and eventually I get a good one.

I'm no expert here, but the mechanism would be something like that.

No one can know for sure what exactly happened 4 billion years ago, though there are some hints in a nebulous fossil record. I believe the best evidence is that a lot of this can be reproduced in lab environments suggesting this is what could have happened.

RBG