慧眼闪闪

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. 2. What is even more important is that as the earth cooled down, water began to appear on its surface. 3. It was not immediately obvious that water was to be fundamental to the development of life. 4. whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved.

What do the sentences have in common?

Module Verbs