Ancient lake

Twelve of the 20 ancient lakes have existed for more than 2.6 million years[citation needed], the full Quaternary period.

In ancient times it was indisputably a true lake, but today it is saline and directly connected to the sea, leading many to consider it a large lagoon or bay.

Factors that influence the water level decreasing include fluvial-lacustrine sediment build-up, evaporation, natural drainage, and geophysical processes.

The location of the graben above the active rift zone results in a lake bottom that is constantly dropping in-depth and walls increasing in height.

Evolutionary characteristics including sexual selection, adaptive radiation and punctuated equilibrium are studied in ancient lakes due to their prolonged existence and general geographic isolation.