The shallow seas became a frozen graveyard. 浅海变成了冰冻的坟墓

169. Little by little, the sea started to freeze.
     海洋逐渐开始冰冻
170. For the inhabitants of Earth's once tropical waters,
     过去地球上热带水域的“居民们”
171. this was a catastrophe.
     大难临头
172. The shallow seas became a frozen graveyard.
     浅海变成了冰冻的坟墓
173. The world's first mass extinction.
     这是世界上第一次大规模灭绝
174. The fatal freeze was caused by a 60% drop in carbon dioxide.
     致命的冰冻 是由二氧化碳减少60%所导致
175. Without this greenhouse gas to warm it,
     没有了温室气体保暖

来自《我们星球上的生命 第一季 第二集 Life on Our Planet S01E02 第一前线》第 172 行