About two million years ago, lava dammed up a river in western Asia and caused a small lake to form  The lake existed for about half a million years  Bones of an early human ancestor were recently found in the ancient lake-bottom sediments that lie on top of the layer of lava
Ttherefore, ancestors of modern humans lived in western Asia between two million and one-and-a-half million years ago
The bones were already in the sediments by the time the lake dried up.