The Namib Desert is often referred to as the world's oldest desert and has been in existence for some 43 million years, remaining unchanged in its present form for the last 2 million years. The Namib is an immense expanse of relentlessly moving gravel plains and dunes of all shapes and sizes that stretch along the entire coastline. The most widespread and dominant type of desert sand dune are linear dunes, with crescent shaped dunes common along the coast and clusters of star dunes.