Earth's early atmosphere was primarily composed of hyrogen cyanide and carbon monoxide.

oxygen and carbon monoxide.

oxygen and water vapor.

carbon dioxide, water vapor and nitrogen.

The correct answer is ''carbon dioxide, water vapor and nitrogen.''

Explanation:

About 4.5 billion years ago, Earth was a very geologically active planet. So many volcanic fumes formed the primitive atmosphere, which was mostly made up of water vapor, carbon dioxide, sulfur, and nitrogen. At this point, oxygen was barely present and the oceans did not yet exist. The primitive atmosphere is the one before the Precambrian, it was reductive, that is, it lacked free oxygen, and only had ammonia, methane and hydrogen, the high temperature of the atmosphere in its early stages facilitated the reaction of these gases to form organic compounds from which life may have emerged. UV rays passed, because ozone did not exist.