1．(教材P25)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.
2．(教材P25)The earth became so violent that it was not clear whether the shape would last or not.
3．(教材P26)What is even more important is that as the earth cooled down, water began to appear on its surface.
4．(教材P26)It was not immediately obvious that water was to be fundamental to the development of life.
5．(教材P26)What many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas.
