High levels of ____ could indicate life on other planets.
A) free nitrogen
B) carbon dioxide
C) free oxygen
D) bound nitrogen

Question

Quizplus · Accepted Answer

Oxygen in itself is a very reactive element. It binds quickly to other materials. Remember, free oxygen only became abundant in our atmosphere when photosynthetic organisms began producing more. Thus, if there is a large amount of free oxygen, then there is something present that is replacing it in the atmosphere. This is likely to be a life-form of some sort. Information can be found in the section Are There Other Ocean Worlds.

High Levels of ____ Could Indicate Life on Other Planets