The text mainly tells the formation of the earth and the development of life on it.The universe began with a "Big Bang".At first,the earth was a cloud of dust,later the earth became a solid ball.On base of the atmosphere,as the earth cooled down,water began to appear .Later,some small plants grow on the water,then shelfish and other fish appear.Next,green plants began to grow on land.Then the insects and amphibians appear.After that,thereptiles,the dinosaurs appear step by step.With so many conditions,at last,mammals,including humans appear.