Why does it seem unlikely life appeared more than once? My understanding was that when life started, the conditions were optimal for complex molecules to form (warm water, lots of organic compounds) so around that time (give or take half a billion year) it may have happened, but in very similar ways.
All known lofe on Earth uses the same base “toolset” to keep it simple while genetic analysis shows all known life is at least distantly related. While it isn’t impossible that life developed multiple times on Earth, any other lineages were unable to compete and died off quickly.
It should also be noted how dramatically easier it is for existing life forms to hog all the available resources than it is for said resources to go through biogenesis. This is why scientists are unable to create life forms in labs, because no matter how sterile we try to make the conditions, some microbe finds a way in and thrives on the resoirce dense media that scientists are trying to recreate life with.
Biogenesis is crazy hard. Once that first lifeform appears it absorbs pretty much all available resources and takes over from there. All those conplex molecules just floating around get incorporated into the life form that appears first. Those primordial seas were constantly churning things about so life would have quickly spread across the ocean once it formed.
But that applies to life as we know it today right? The first life forms couldn’t have taken over the earth instantly, they weren’t battle hardened bacteria, but very simples beings, not far from overly complex proteins. Probably took at least some million years for a microbe to spread around the earth, just from the sheer size of it. So in that time, life could originate from other similar primordial soups.
Once they get going they reproduce like crazy. And there wouldn’t have been any competition for that first life form, so is growth would only be hindered by how many nutrients were available. Churning oceans and storms would have spread that first life form would only needaybe a couple centuries millenia to spread across the Earth, while that leap from self replicateling macromolecules to actual life form would have simultaneously been way harder tham you think.
