一种生物产生的废料可能却是另一种生物所必需的。最明显的例子就是氧气,它是植物和一些微生物产生的一种光合作用的副产品,但却被动物吸入体内。然而情况并非一直如此。新的研究显示,地球早期氧气含量很低,这意味着远古的“光合作用者”们很可能转而将水作为一种废物排出体外。 Waste from one organism may be necessary for another. The most obvious example is oxygen, a byproduct of photosynthesis produced by plants and some microbes, but inhaled by animals. However, this is not always the case. New research shows that the early oxygen content of the Earth is low, which means that ancient “photosynthesisers” are likely to switch to excreting water as a waste.