| 1. | At some time more than five billion years ago the universe started .
在50亿年前的某个时候，宇宙开始形成。 |
| 2. | Yet oxygen gas did not begin to accumulate in the atmosphere until about 2 billion years ago .
但是大约在20亿年前，氧气才开始在大气层中积累。 |
| 3. | The organisms living between 3 and 1 billion years ago were not as versatile as modern species, probably due to energy limitation .
生活在过去二十亿年之间的有机体可能由于能量的限制，不如现代物种这样五花八门。 |
| 4. | Our solar system was formed 4 . 6 billion years ago
我们的太阳系被形成了4 . 6十亿年前。 |
| 5. | The supernovae exploded between 3 . 5 and 10 billion years ago
超新星爆炸时间在35 - 100亿年前。 |
| 6. | What prompted the leap in complexity starting 1 . 5 billion years ago
那么是什么推动了发生在15亿年前的复杂性的飞跃呢？ |
| 7. | About 5 billion years ago
五十亿年以前 |
| 8. | About 13 . 7 billion years ago a tremendous explosion started the expansion of the universe
大约13 . 7十亿年前巨大爆炸开始了宇宙的扩展。 |
| 9. | Just as the solar system was forming some 4 . 6 billion years ago , it turned itself inside out
太阳系的形成发生在大约46亿年前，那会儿它里外翻了个身。 |
| 10. | For example , the researchers date the split between plants and animals at 1 . 6 billion years ago
例如，研究者确定植物和动物大概是在16亿年前开始产生差异。 |
