The oldest objects found so far in our solar system are Earth rocks that are 3.9 billion years old. ...

The oldest objects found so far in our solar system are Earth rocks that are 3.9 billion years old.
 
  Indicate whether the statement is true or false

Question 2

When considering the number of technologically advanced civilizations in our Galaxy, it is useful to consider
 
  a. the average life span of an alien.
  b. the average life span of the civilization.
  c. the distance to the civilization's planet.
  d. the type of advanced communication they use.

Question 3

A planet found orbiting a star other than the sun is called a(n) ____________________.
 
  Fill in the blank(s) with correct word

Question 4

What is important about the habitable zone around a star that makes astronomers believe life could exist there?
 
  a. The level of UV radiation from the star is minimal there.
  b. Only in the life zone can complex organic molecules be found.
  c. Planets in the life zone will always have oxygen atmospheres.
  d. In the life zone water can exist as a liquid.

Question 5

The ____________________ of a radioactive substance is the amount of time for the substance to be reduced by half.
 
  Fill in the blank(s) with correct word