[中学联盟]浙江省杭州市塘栖中学高中英语必修三教学课件：unit4 How life began on the earth(final).pptVIP

* Blackboard, timeline solar system But scientists now think Pluto is too small to be called a planet. Water had also appeared on other planets like Mars but, unlike the earth, it had disappeared later. What many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas. ④This produced a chain reaction, which made it possible for life to develop. It was not immediately obvious that water was to be f_________ to the development of life. Para.3: the importance of water for life Para.3 undamental No one knows exactly how the earth began, After that, atoms began to form and combine to create stars and other bodies. However,according to a widely accepted theory, the universe began with a “Big Bang” that threw matter in all directions. as it happened so long ago. HOW LIFE BEGAN ON THE EARTH Para.1: a widely accepted theory about the formation of the universe Para.1 ‘’Big Bang’’ Thoery ⑤They were in time to produce carbon,nitrogen, water vapour and other gases, which were to make the earth’s atmosphere. 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 earth became so v_____ that it was not clear whether the shape would last or not. What is even more important is that as the earth cooled down, water began to appear on its surface. Para.2 ④ It exploded loudly with fire and rock. iolent a cloud of dust a solid globe explosion atmosphere water Para.2: the formation of the earth Before life appeared Para.3: the importance of water for life Para.1: a widely accepted theory about the formation of the universe Para.2: the formation of the earth Many millions of years later, the first extremely small plants began to appear on the surface of the water. They multiplied and filled the