Deep orange or reddish-brown atmosphere: The second atmosphere’s formation was crucial and occurred just before or alongside the formation of Earth’s oceans, which directly supported the evolution of organic molecules and prebiotic microenvironments. The second atmosphere began to develop around 4.5 to 4 billion years ago, as volcanic outgassing released gases trapped in the Earth’s interior. This process was part of Earth’s differentiation and cooling phase.

Unlike the first atmosphere, the second was rich in water vapor, carbon dioxide, nitrogen, and other volcanic gases such as sulfur compounds and small amounts of ammonia and methane. Notably, it lacked free oxygen.

The cooling of Earth and the condensation of water vapor from volcanic outgassing led to the formation of Earth’s oceans. This means the second atmosphere’s development was critical for creating the conditions necessary for ocean formation.