Arabia Deserta

Here's a release about a climate prehistory of Arabia.

Arabia used to be savannah, with lakes. 6200-6000 BC, the place got so dry that the locals switched to herding. Further droughts struck 5500-5200 and 4500-4300 BC; these led to the herds moving to the coast and the interior concentrating more on trade. Over 3900-3300 BC, the southwestern peninsula dried out to such an extent those locals were done with the place, and migrated to the Gulf Coast and Oman.

After circa 3000 BC, we get linguistic evidence. Semitic is west of the upper Euphrates, and paraSemitics like Akkadian to the east and downstream. At the Euphrates and Tigris delta to the Gulf, is Sumerian. Elamite east of that, probably. On the other side of the Red Sea across from Yemen: Cushitic, generally considered related to Semitic. Tho' this last is inferred from loanwords in Ethiopian Semitic, as reconstructed 800 BC.

According to this paper, the Arabians of that time didn't venture south. That agrees firstly with the divergence between Cushitic and Semitic being (much) wider than a post-6200 migration should allow, and with the lack of para/pre Semitic loans in the Cushitic languages. Secondly with Cushitic's loans being otherwise East African as far as we know.

Most assume that the Elamites got to the Near East from what's now Iran. I wonder if the Arabians at this time were the ancestors of the Sumerians.