The habitable zone is the area around a star where: A) planets ...

[luvbio]

The habitable zone is the area around a star where:
 
  A) planets with life have been found.
  B) human beings could live.
  C) the Greenhouse Effect is possible.
  D) a planet could have an atmosphere.
  E) temperatures are suitable for planets to have liquid water.

Question 2

Why does detection of abundant free oxygen in an atmosphere suggest life is present? Does its absence prove life could not be present?
 
  What will be an ideal response?

[lkanara2]

Answer to Question 1

E

Answer to Question 2

Oxygen is highly reactive, and unless quickly replaced by photosynthesis, would soon disappear into surface rocks, as it has on Mars and Venus. However, life on Earth certainly evolved before it released the abundant present oxygen, and on other worlds, photosynthesis may not have evolved. Yet other forms of life may thrive using methane or hydrogen sulfide, all energy processes found here as well.

[luvbio]

TY

[lkanara2]

You're welcome