I seem to recall reading somewhere that 20,000 years ago or so, Japan was connected to the Asian mainland. So what exactly did (the Japanese vicinity of) Eastern Asial look like?
At a glance, it seems as though Japan would connect nicely to Korea in the south, and to Sakhalin Island (probably connected to the mainland in olden days) and possibly thru the Kuril Islands to the Kamchatka peninsula in the north.
Would there have been a large “inland sea,” or just a great plain that eventually got flooded?
We ain’t talking Pangea or Gondwanaland time frames, so this shouldn’t be hard to figure out, but I haven’t had any luck.