To me, this rock is the history of Earth, the history of biology.

对我来说，这块岩石就是地球的历史，生物的历史。

After all, they're the largest creatures in the history of Earth — both in the sea and on land!

毕竟，它们是地球历史上最大的生物——无论是在海里还是在陆地上！

This is the first point in the four and a half billion year history of Earth that it has been possible.

这是地球45亿年来可以实现的第一点。

That’s because some scientists are thinking about changing the system we use to describe the history of Earth.

那是因为一些科学家正在考虑改变我们用来描述地球历史的系统。