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.

• 经过很长的时间，由于大气层中氧含量的增加，地球变成更适合于植物生长的地方，植物生成更多的氧，逸入大气层，后来，出现了动物。