洞穴 12

Variations in water flow and the air currents produce an infinite variety of forms, but all are created by the same process - the slow deposition of dissolved limestone. And when stalactite meets stalagmite a column is born. Structures like these in North America's Carlsbad Cavern can take many thousands of years to develop. But sometimes the formations in a cave stop growing altogether. These flooded caves in Mexico have remained virtually unchanged for thousands of years. Since the last Ice Age they've become cut off from the outside world. Yet their impact on life of the surface has been huge. 500 years ago they supported one of the world's great civilisations - the Maya.

水流和气流的不同变化会形成千姿百态、形状各异的石笋，但所有石笋都是由同样的过程形成的，这就是溶解的石灰岩缓慢的堆积。钟乳石和石笋相遇之后，就会形成石柱。位于北美卡尔斯巴德岩洞的这些奇观需要成千上万年才能形成。但有时在某个洞穴中这一过程会完全停止下来。墨西哥的这些洪水淹过的洞穴的结构成千上万年来几乎没有任何改变。自从上一个冰河期之后，它们与外面的世界完全隔绝了，但它们对于地面生命的影响却是巨大的。它们曾经托起了世界上最伟大文明之一的玛雅文明。