The earth was just ____ cloud of dust after the “Big Bang”. The earth exploded ____(loud) with fire and rock. They were in time to produce carbon, nitrogen, water vapour and other gases, which were ____(make) the earth's atmosphere. As the earth cooled down, water began to appear on its surface. It allowed the earth to dissolve ____(harm) gases. Then life began to develop.

    Small plants multiplied and filled the oceans and seas with oxygen. This encouraged the ____(develop) of early shellfish and fish. Land animals such as insects, reptiles and dinosaurs ____(appear) after green plants came into being. Small clever animals spread all ____ the earth. They are putting too much carbon dioxide into the atmosphere, ____ prevents heat from escaping from the earth into space. ____ life will continue on the earth for millions of years to come will depend on whether this problem can ____(solve).