Many scientists today are convinced that life exists elsewhere in the universe---life probably much like that on our own planet. They reason in the following way.
As far as astronomers can determine, the entire universe is built of the same matter. They have no reason to doubt that matter obeys the same laws in every part of the universe. Therefore, it is reasonable to guess that other stars, with their own planets, were born in the same way as our own solar system. What we know of life on earth suggests that life will arise wherever the proper conditions exist.
Life requires the right amount and kind of atmosphere. This eliminates all those planets in the universe that are not about the same size and weight as the earth. A smaller planet would lose its atmosphere; a larger one would hold too much of it.
Life also requires a steady supply of heat and light. This eliminates double stars, or stars that flare up suddenly. Only single stars that are steady sources of heat and light like our sun would qualify.
Finally, life could evolve only if the planet is just the right distance from its sun. With a weaker sun than our own, the planet would have to be closer to it. With a stronger sun, it would have to be farther away.
If we suppose that every star in the universe has a family of planets, then how many planets might support life? First, eliminate those stars that are not like our sun. Next eliminate most of their planets; they are either too far from or too close to their suns. Then eliminate all those planets which are not the same size and weight as the earth. Finally, remember that the proper conditions do not necessarily mean that life actually does exist on a planet. It may not have begun yet, or it may have already died out.
This process of elimination seems to leave very few planets on which earthlike life might be found. However, even if life could exist on only one planet in a million, there are so many billions of planets that this would still leave a vast number on which life could exist.
1. Astronomers believe that matter in different parts of the universe
A) has different laws.
B) has one common law.
C) shares the same laws
D) shares no common law.
2. The existence of life depends on all of the following factors EXCEPT
A) the right amount of atmosphere.B) our own solar system.
C) steady heat and light D) the right distance from the sun.
3. Which of the following statements is INCORRECT?
A) The planet must be as big and heavy as the earth.
B) Proper conditions are essential to the existence of life
C) Double stars can provide steady light and heat.
D) The distance between a planet and its sun should be right.
4. What kind of planet might NOT support life?
A) Most of the planets of the stars.
B) Stars similar to our sun.
C) Planets similar to the earth.
D) Planets with proper conditions.
5. At the end of the passage the author suggests that
A) it is impossible for life to exist on planets.
B) earthlike life could only exist on a few planets.
C) life could exist on only one planet in a million.
D) life could exist on a great number of planets.
KEY:CBCAD
初一英语日记:暑假英语日记--暑假第一天
初一英语作文:暑假英语作文--A New Term Began
初一英语作文范文:My Happiest Day
初一英语作文:A letter to Uncle Wang
初二英语作文:Lucky Numbers
初一英语作文范文:Introduction of myself
初一英语作文范文:A Plan For A Day Out
初二英语作文:My Teacher
初一英语作文:暑假英语作文--The Summer Holiday
初二英语作文:My Dream
初二英语作文:A Young Pioneer
初一英语作文范文:Summer Camp
初一英语作文范文:My Dream
初一英语作文范文:Let's peotect our eyes
初一英语作文范文:My favorite movies
初一英语作文范文:cry
初一英语作文范文:the First Day of Spring Festival
初一英语作文范文:My summer holiday
初一英语作文范文:An English Class
初一英语作文范文:My Net Friend
初一英语作文范文:My Class
初二英语作文:Do Not Give Up
初二英语作文:Information Age
初一英语作文范文:My Dream House
初二英语作文:My pasttime
初一英语作文范文:It is time for sports
初一年级暑假英语日记汇总(带翻译)
初一英语作文:暑假英语作文--A Letter
初一英语日记:暑假英语日记--乡村游记
初二英语作文:Friendship
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |