Which highly reactive gas was probably absent from the Earth's primitive atmosphere?
A)methane
B)carbon dioxide
C)O₂ (oxygen gas)
D)water vapor

Question

Quizplus · Accepted Answer

Oxygen gas (O₂) was probably absent from the Earth's primitive atmosphere. This is because the Earth's atmosphere lacked oxygen until about 2.4 billion years ago when photosynthetic organisms began producing it as a byproduct. Prior to this, the atmosphere was composed mostly of nitrogen, carbon dioxide, and water vapor, with smaller amounts of methane, ammonia, and other gases.

Which Highly Reactive Gas Was Probably Absent from the Earth's