Became too salty. [1] Bottoms grew increasingly heavy from meteor accumulation; sank. [2] Currents shifted in Pleistocene; little changed in last 15 million years. [3] Named. None on Jerusem or Edentia. [4] Not all inhabited planets have. [5] Originally fresh; attained requisite saltiness. [6] Protection of oceans allowed North America to develop unmolested. [7] Sunlight can penetrate 600 feet. [8] Weight relative to land elevations. [9] World-wide. [10]