is pulled back to Earth by gravity. 被地心引力拉回地球
is tumbling towards Earth at 100,000 kilometers per hour. 正以每小时10万公里的速度坠向地球
they have ruled planet Earth for a staggering 150 million years. 它们已统治地球长达1.5亿年
they've evolved to exploit almost every habitat on Earth. 它们进化出了 适应地球上几乎每一个栖息地的能力
form some of the largest herds the Earth had ever seen. 形成了地球史上最大的兽群
...in ways that would revolutionize life on Earth. 这样的改变将为地球上的生物 带来革命性的变化
...the biggest animals to ever walk the Earth are on the rise. 地球上有史以来最大的动物正在崛起
Since life first emerged on planet Earth, 自从生命首次在地球上出现