The Namib desert is considered one of the oldest deserts in the world, having endured arid or semi-arid conditions for at least 55 million years after the Atacama Desert. Its aridity is caused by the descent of dry air of the Hadley Cell, cooled by the cold Benguela current along the coast. It has less than 10 mm (0.4 inches) of rain annually and is almost completely barren.
