She says there are twolayers showing the association, one about 30,000 years old, the other 35,000 years old.
她说有两层显示了这种联系,一层有大约3万年历史,另一层3万5千年。
2
Because of the cold temperatures, the tundra has twolayers: top layer, which is called the active layer, is frozen in the winter and spring, but thaws in the summer.
由于寒冷的气温,冻土带有两层:最上面的一层被称为活动层,在冬季和春季被冻结,但在夏季解冻。
3
The overlap of the twolayers creates a moiré effect.