1. What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe. (P25).
... be to do 在此句中表示不可避免将要做的事或命中注定的事。如：
This experience was to change his life.
This discovery was to have a major effect on the treatment of heart disease.
【拓展】 a. be to do 还可以表示命令、义务、职责等，译为“应该，必须”，多用于长辈对晚辈，上级对下级等。如：
You are to eat all your supper before you watch TV.
b. be to do 还可以表示按计划约定要做的事。常用于正式文件中。如：
They were to get married in May.
【练习】 完成句子：
1) As a child, he never knew __________________ (他会成为) a famous singer.
2) The Prime Minister __________________ (将访问) Budapest.
3) You __________________ (不可以吸烟) in this room.
