Question

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

Answer 1

Oxygen gas was most likely absent from Earth's primitive atmosphere.  The current theory is that the Earth's early atmosphere was composed of mainly carbon dioxide and methane due to the high volcanic activity.  Cyanobacteria and their use of photosynthesis was what caused earth's atmosphere to become oxygen enriched.
I hope that helps.

Answer 2

The highly reactive gas that was probably absent from the Earth's primitive atmosphere is oxygen.

The atmosphere refers to the thin layer of gas above the earth's crust. This thin layer of gases is composed of a mixture of gases. The earth's primitive form also had an atmosphere.

However, we must recall that in its primitive form the earth was mostly under reducing conditions and there was no oxygen. However, photosynthesis by plants increased the oxygen content of the earth.

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