And these plants need sunlight, so we know when we find that sediment there's no ice overhead. And we saw about 35 alternations between open water and ice-covered water, between gravels and these plant sediments.
这些植物需要阳光， 所以当我们发现这沉积物时， 我们知道原来它上面本没有冰。 我们在开放水域和冰层覆盖的水域中 看到大约35次这些砾石和 植物沉积物的交替变化。