| 1. | It has a half-life of about 41/2 billion years .
它的半衰期大约为45亿年。 |
| 2. | 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。 |
| 3. | The sun has been emitting energy at this rate for billions of years .
太阳以这样的强度辐射已有10亿年之久。 |
| 4. | As a slowly contracting dwarf the star may remain luminous for billions of years .
收缩较慢的白矮星仍会发光几十亿年。 |
| 5. | By this means the age of the earth had been estimated at several hundred million years .
用这个办法推算出地球的年龄是数亿年。 |
| 6. | The oldest sediments cored to date are about 150 million years old .
到目前为止取出的最老沉积物的岩心是大约15亿年以前的生成。 |
| 7. | Their ancestors have been eating according to flavor for upwards of a billion years .
他们的祖先已经根据滋味来吃东西吃了十亿年以上了。 |
| 8. | 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。 |
| 9. | Now that curtain has risen and men can look back to a past of scores and hundreds of millions of years .
帘幕已揭开，人们可以回溯几十亿年之久的过去了。 |
| 10. | Meteorites have also been analysed, and a few of them appear to be not less than 7, 000 million years old .
有人分析过陨石，其中只有少数陨石的年龄似乎在70亿年以上。 |
