一旦光合作用上升了大气氧气成水平足够高，臭氧层被形成，意味，它是然后可能为生存事冒险土地。
Once photosynthesis had raised atmospheric oxygen levels high enough, the ozone layer formed, meaning that it was then possible for living things to venture onto the land.
一旦光合作用上升了大气氧气成水平足够高，臭氧层被形成，意味，它是然后可能为生存事冒险土地。
Once photosynthesis had raised atmospheric oxygen levels high enough, the ozone layer formed, meaning that it was then possible for living things to venture onto the land.
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