Which gases were present in the primitive atmosphere?

• A. Nitrogen, Oxygen, Carbon Dioxide
• B. Ammonia, Methane, Hydrogen
• C. Helium, Argon, Oxygen
• D. Carbon Monoxide, Sulfur Dioxide, Nitrogen

Answer: (B)

The correct choice identifies ammonia, methane, and hydrogen as the gases present in the primitive atmosphere, based on scientific theories about the origins of Earth's atmosphere. Early in Earth's history, the atmosphere was likely composed of these gases, which contributed to the conditions necessary for the development of life.

Ammonia (NH3) and methane (CH4) are both associated with reducing environments, which are thought to have been prevalent during the early stages of Earth's development. Hydrogen (H2), being the most abundant element in the universe, was also likely abundant in the early atmosphere. These gases created a chemically reactive environment, which, when exposed to energy sources such as lightning or ultraviolet light, could lead to the formation of complex organic molecules.

Other options include gases that either do not represent the early atmosphere accurately (like oxygen which evolved later due to photosynthetic processes) or consist of noble gases that were less relevant in the context of the early reactions necessary for the origins of life. Understanding the composition of the early atmosphere helps in comprehending how life on Earth began and the transformations that have taken place over geological time.