Earth's early atmosphere developed from which source?

• A. The atmosphere formed from solar wind.
• B. Gases released by volcanoes condensed to form Earth's early atmosphere.
• C. The atmosphere formed from dissolved gases in the ocean.
• D. The atmosphere formed from photosynthesis.

Answer: (B)

Volcanic outgassing from Earth’s interior supplied the first atmosphere. As the planet formed and cooled, gases trapped inside—mainly water vapor, carbon dioxide, and nitrogen—were released by volcanoes and accumulated to form the early atmosphere. This explains why the original envelope was rich in greenhouse gases and lacked free oxygen. The other options don’t fit as the primary source: solar wind doesn’t create a stable atmosphere, dissolved gases in the ocean would contribute only after oceans existed and are not the initial source, and photosynthesis would add oxygen later in Earth’s history, not form the initial atmosphere.