Most of Kakadu was under a shallow sea approximately 140 million years ago , with the escarpment wall formed from sea cliffs and Arnhem Land from a flat plateau above the sea .
Most of Kakadu was under a shallow sea about 140 million years ago , with the escarpment wall formed from sea cliffs and Arnhem Land from a flat plateau above the sea .
Released in 2005 , a study by four respected academics contained a proposal to replace the Thames Barrier with a more ambitious 16 km ( 10 mi ) long barrier across the Thames Estuary from Sheerness in Kent to Southend in Essex .