Around two million years ago, the Jordan valley at the northern end of the East African Rift System, was part of a long embayment of the Mediterranean Sea. A million years later, tectonic activity raised the land to the west, isolating this embayment from the Mediterranean and creating a large salt-water lake.  Cut off from the sea in an arid climate, the lake began to shrink due to evaporation and became more saline. As the Jordan valley continued to subside, the lake gradually evolved into the modern Dead Sea.

A talk by Richard Fletcher.