The East Siberian Sea is bound to the south by the East Siberian Lowland, an alluvial plain mainly composed of sediments of marine origin dating back to the time when the whole area was occupied by the Verkhoyansk Sea, an ancient sea at the edge of the Siberian Craton in the Permian period. As centuries went by, gradually, most of the area limiting the sea, as well as the contiguous Laptev Sea to the south became filled with the alluvial deposits of modern rivers.