Question

Which gas was not part of Earth’s original atmosphere?


carbon dioxide

water vapor

nitrogen

oxygen

Answer 1

Oxygen was not part of Earth's original atmosphere. The early atmosphere, formed shortly after the planet's formation about 4.5 billion years ago, was primarily composed of gases like carbon dioxide, water vapor, nitrogen, and other volcanic gases, but it lacked free oxygen. Oxygen became a significant component of the atmosphere much later, primarily due to the photosynthetic activities of microorganisms such as cyanobacteria.