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.
Hydrologicly they are one, two lobed lake. But for cultural and commercial reasons they function more as two separate lakes. Similar to how the Adriatic and Aegean Sea are the same body of water as the Mediterranean.