which gas is inferred to have been absent from
earth's atmosphere during the early archean
eon?

Free Oxygen  is inferred to have been absent from  Earth's atmosphere during the Early Archean  Eon.

Explanation:

During the early Archean Eon the free Oxygen was found to be absent. Though water molecules were found and the water molecules contained Oxygen it was found combined with the Hydrogen molecule not as free Oxygen.

Due to the absence of Oxygen only blue green algae was found. But they started to release Oxygen as a waste product. Eventually the Oxygen started to infer into the atmosphere. Due to organic photosynthesis Oxygen accumulated in the atmosphere .

from my research i have to the conclusion that decomposers, such as fungi, bacteria and invertebrates, play a critical role in nutrient cycling and without them the earth's ecosystem may not support life as we know it. elements such as carbon, nitrogen and phosphorus exist in limited amounts on earth, although huge amounts of carbon are being released into the atmosphere from underground sources now by humans. it is still extremely important that other nutrients be retained by the process of re-use. decomposers are organisms that are able to chemically break down dead material and make these elements available for use by other organisms. without this breakdown of dead material, dead bodies would pile up. so decomposers also play a role in clean up also. without them, life might not continue as we know it and dead material would overwhelm the earth.    

c is the answer : )               your welcome