After a very long time, as the amount of oxygen in the atmosphere increased, the earth became a more suitable place for plants to develop. Plants produced more oxygen which was freed into the atmosphere. Later on animals developed.
英
美
- 經(jīng)過(guò)很長(cháng)的時(shí)間，由于大氣層中氧含量的增加，地球變成更適合于植物生長(cháng)的地方，植物生成更多的氧，逸入大氣層，后來(lái)，出現了動(dòng)物。
