海底扩张学说是在大陆漂移学说的基础上所发展出的高端地球地质活动学说。在各大洋的中央有一带状分布的海岭，这些带状海岭是下方地幔软流层的出口。不断涌出的熔岩自海岭流出，冷却而成为刚性强的大洋地壳。大洋地壳不断的受到新由海岭涌出的溶岩所推挤而向两旁移动，使海面积扩大，同时大陆地壳受到推挤而分离。导致海底扩张的原因是海水不平衡的压力导致的板块漂移。

地球上大约3/4的表面由海洋覆盖，海水的总量巨大，对海底以及周围陆地的压力也十分巨大。由于受到月球的引力作用和不同区域海水温度不同等因素的影响，海水对不同板块的压力是不平衡的，这就使得板块发生漂移，同时也就产生了海洋带状岭。

Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. Basaltic magma rises up the fractures and cools on the ocean floor to form new sea floor. Older rocks will be found farther away from the spreading zone while younger rocks will be found nearer to the spreading zone.