地史时期森林的变迁主要是由于生态环境的变动；

The former is due to the variations of the ecological factors.

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当然，我们现在谈论的是地史时期，是以数万年测量的。

Of course, we're talking geological time here, which is measured in tens of thousands of years.

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最后，对潮汐韵律层在推测地史时期地-月系的演化历史中的意义作了评述。

Finally, the implications of tidal rhythmites for the Earth's rotation and the history of the Earth-Moon system in geological past are concluded.

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