Question

What was the Earth's first atmosphere like?

Mostly nitrogen, carbon dioxide, water vapor

Mostly nitrogen and about 15% oxygen

Predominantly hydrogen and helium, much like Jupiter and Saturn

Methane, hydrogen and ammonia

Answer 1

The Earth's first atmosphere was predominantly hydrogen and helium, much like Jupiter and Saturn. This early atmosphere was likely formed from the gases present during the planet's formation and was eventually lost to space due to the low gravitational pull of the young Earth and the high-energy conditions of the early solar system. Over time, volcanic outgassing and the release of gases from within the planet contributed to the formation of a secondary atmosphere, which was characterized by higher levels of water vapor, carbon dioxide, and other gases, but the initial atmosphere was primarily made up of hydrogen and helium.