某肥牛育肥基地及屠宰加工厂可行性研究.doc

one knows exactly how the earth began, as it happened so long ago. However, according to a widely accepted theory, the universe began with a “ Big Bang “ that threw matter in all directions. After that, atoms began to form and combing to create stars and other bodies.?For several billion years after the “ Big Bang “, the earth was still just a cloud of dust. 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. The earthenware became so violent that it was not clear whether the shape would last or not. It exploded loudly with fire and rock. They were in time to produce carbon, nitrogen , water vapour and other gases , which were to make the earth’s atmosphere. What is even more imprtant is that as the earth cooled down, water began to appear on its surface.?Water had also appeared on other planets like Mars but, unlike the earth, it had disappeared later. It was not immediately obvious that water was to be fundamental to the development of life. What many scientists believe is that the continued persence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas. This produced a chain reaction, which made it possible for life to develop.?Many millions of years later, the first extremely small plants began to appear on the surface of the water. They multiplied and filled the oceans and seas with oxygen, which encouraged the later development of early shellfish and all sorts of fish. Next, green plants began to grow on land. They were followed in time by land animals. Some were insects. Others, called amphibians, were able to live on land as well as in the water. Later when the plants grew into forests, reptiles appeared for the first time. They produced young generally by laying eggs. After that, some huge animals, called dinosaurs, developed. They laid eggs too and existed on the earth for more than 140 million years. However, 65 million years ago the age of the dinosau