Two and a half million years ago, 250万年前

34. and the relief of spring.
    和春天的到来
35. But there was a time
    但曾经有一个时期
36. when winter never seemed to end.
    冬天似乎永远不会结束
37. Two and a half million years ago,
    250万年前
38. changes in the Earth's orbit, ocean currents, and carbon dioxide levels
    地球轨道、洋流 和二氧化碳水平的变化
39. led to an abrupt cooling of the planet.
    导致地球温度骤降
40. The great Ice Age had begun...
    冰河时期开始

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 37 行