橄榄树一直是宝贵的食物和石油来源。
The olive tree has always been a valuable source of food and oil.
当树中空或部分死亡时，它为小动物提供了一个家，也成为了许多其他动物的食物来源。
When a tree becomes hollow or part of it becomes dead, it provides a home for small animals and is a source of food for many other animals.
现在看起来这些以甲烷为基础的食物链和纯粹的无脊椎动物相比，更可能会延长生命树，可能这种情形已经持续了数百万年。
It now seems, though, that such methane-based food chains may stretch farther up the tree of life than mere invertebrates-and may have done so for millions of years.
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