there have been more than 50 cycles of ice buildup and melt... 已经发生50多次结冰融化的循环

169. The indelible scars of this megaflood
     大洪水造成的无法磨灭的痕迹
170. still mark the American landscape today...
     如今仍在美国的地貌上显现
171. yet since the dawn of the Ice Age,
     然而自从冰河时期起始之时
172. there have been more than 50 cycles of ice buildup and melt...
     已经发生50多次结冰融化的循环
173. each causing its own epic floods.
     每一次都引发了大规模洪水
174. Once the turmoil of the last great melt subsided,
     上一次大规模融化引起的混乱 平息之后
175. balance slowly returned across the land.
     大地逐渐恢复平衡

来自《我们星球上的生命 第一季 第八集 Life on Our Planet S01E08 冰与火的世纪》第 172 行