No one knows exactly the earth began. According to a widely accepted theory, the earth began with a “Big Bang”,exploded loudly and produced water vapor and many gases， (make) the earth's atmosphere. As the earth cooled down, water appeared and stayed the surface. It was the presence of waterallowed the earth to dissolve harmful gases and acids into the oceans and seas, which made possible for life to develop. First, the appearance of small plants encouraged the development of early shellfish and all sorts of fish. Next, green plants began to grow on land. were followed by land animals. So reptiles appeared for the first time. Later, dinosaurs developed.they suddenly disappeared. After that, mammals came into being. Finally, humans appeared and spread all over the earth. However, they are putting too much carbon dioxide into the atmosphere, making the earth too hot(live) on. So whether life will continue on the earth will depend on this problem can be solved.
