950 millions years ago Urantia presents the picture of one great continent of land and one large body of water, the Pacific Ocean.  The sea bottoms are more dense than the land masses, and this is what keeps the continents above water. 
Began 750 million years ago.  Continents tend to creep into oceans.  500 million years ago Greenland and the arctic land mass, together with North and South America, were beginning their long and slow westward drift. 
The great Cretaceous period is the times of the termination of the westward and southward drift of the continents, accompanied by tremendous crustal deformations and concomitant widespread lava flows and great volcanic activities. 
The great Cretaceous period was drawing to a close, and its termination marks the end of the great sea invasions of the continents. These alternate periods of land and sea dominance have occurred in million-year cycles.