But scientists now think Pluto is too small to be called a planet.
① Water had also appeared on other planets like Mars but, unlike the e
arth, it had disappeared later. ②It was not immediately obvious that water was to be f_________ undamental to the development of life. ③What 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. Para.3: the importance of water for life
Para.1 HOW LIFE BEGAN ON THE EARTH ?No 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” ??Big that threw matter in all directions. ?After that, atoms began to form and combine to create stars and other bodies. Para.1: a widely accepted theory about the formation of the universe
Para.2 ①For several billion years after the “Big Bang”, the earth was still just a cloud of dust. ②What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe. ③The earth became so v_____ iolent that it was not clear whether the shape would last or not. ④ It exploded loudly with fire and rock. ⑤They were in time to produce carbon,nitrogen, water vapour and other gases, which were to make the earth’s atmosphere. ⑥What is even more important is that as the earth cooled down, water began to appear on its surface.
a cloud of dust
a solid globe
atmosphere explosion Para.2: the formation of the earth
Before life appeared
Para.1: a widely accepted theory about the formation of the universe
Para.2: the formation of the earth Para.3: the importance of water for life
Para.4 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 land animals Some were followed in time by___________. were______. insects Others, called________, amphibians were able to live on land as well as in the water. forests Later when the plants grew into_______, reptiles ________appeared for the first time. They produced young generally by laying eggs.
Para.4 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 dinosaurs ended. Why they suddenly disappeared still remains a mystery. puzzle This disappearance made possible the rise of mammals on the earth. These animals were different from all life forms in the past, because they gave birth to young baby animals and produced milk to feed them.
Dinosaurs Reptiles Land animals Para.4: the development of plants and animals on the earth Forests
Shellfish & fish
Plants on land
Small Plants in the water
Para.5 Finally about 2.6 million years ago some small clever animals, now with hands and feet,appeared and spread all over the earth.Thus they have, in their turn, become the most important animals on the planet. Para.5: the arrival of humans and their impact But they are not looking after the earth on the earth very well. They are putting too much carbon dioxide into the atmosphere, the which prevents heat from escaping from problem caused the earth into space. As a result of this, many scientists believe by the earth may become too hot to live on.So humans whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved.
They developed new methods of growing food, hunting and moving around.
The development of life
Para.4: the development of plants and animals on the earth
Para.5: the arrival of humans and their impact on the earth
（8）A （ ）B 10 （3 ）C （5 ）D （9 ）E （7 ）F （2 ）G （4 ）H （6 ）I （1）J 12 （ ）K （ ）L 11
Insects and amphibians appeared. Dinosaurs appeared. The earth became a solid ball. Small plants grew on the water. Reptiles appeared. Plants began to grow on dry land. The earth was a cloud of dust. Water appeared on the earth. Shellfish and other fish appeared. The universe began with a “Big Bang”. Clever animals with hands and feet appeared. Mammals apeared.