1 .         No one knows exactly     1     the earth began, as it happened so long ago.     2     , according to a     3     (wide) accepted theory, the universe began with a “Big Bang” that threw matter     4     all directions. After that, atoms began to form and combine to create stars and other bodies.
        Water     5     (appear) on other planets like Mars but, unlike the earth, it had disappeared later.     6     was not immediately obvious that water was to be fundamental to the development of life. What many scientists believe is that the continued     7     (present) of water allowed the earth     8     (dissolve) harmful gases and acids into the oceans and seas. This produced     9     chain reaction,     10     made it possible for life to develop.