The causes for the occurrence of this phenomenon are the influences of the sea-level rise and climatic change in the Mid Cretaceous.

该现象发生的原因是白垩纪中期的海平面上升和气候变化的影响。

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Before the mid-Cretaceous, 100 million years ago or so, flowering plants were scarce: conifers and their relations ruled the landscape.

白垩纪中期之前，也就是说大约1亿年前，开花植物很少见：裸子植物占据着地球的景观。

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