Hello, Ali, it was much less of a desert around 6000 B.C. than it is now. "The southern frontier of the desert was far to the north of where it is now" means that the bottom border of the desert was much further north then which would mean that the desert was much smaller then. "Semiarid grassland and shallow freshwater lakes covered much of what are now arid plain" means that much of what is now the desert was lakes and grassland back then. Hope that helps.

Olivia is correct. 6000 years ago, the southern frontier/border/boundary of the desert was far to the north of where it is now. I.e. the edge of the desert has moved south wards since that time. Perhaps the northern edge of the desert has moved northward too, to come close to the coast. I don't know, but it might be reasonable. Semi-arid grassland and shallow freshwater lakes covered much of the area which is now arid. How do we know this???? There are wadis, and there are rock paintings throughout that desert. In the rock paintings there are hippos (hippopotamuses), gazels, antelope, etc. Hippos need water, and gazels, antelope, etc need grass, not desert. I don't remember if the rock painting showed people fishing, but there were people and there were animals and water animals, in the area which is now desert. The climate has changed. The world was created fertile, and lush.