The Earth's Early Atmosphere

This lesson explores the composition and characteristics of the Earth's early atmosphere in greater detail, as required by AQA GCSE Chemistry specification (5.9.1). You need to understand what gases were present, where they came from, and why the early atmosphere was so different from the one we have today. This lesson builds on the overview of atmospheric history and focuses specifically on the first phase — the period dominated by volcanic outgassing.

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The Origin of the Early Atmosphere

When the Earth first formed about 4.6 billion years ago, it was an extremely hot, molten mass. As the surface began to cool, a thin solid crust formed. Beneath this crust, the mantle remained hot and partially molten, driving intense volcanic activity. These volcanoes released vast quantities of gases in a process called outgassing (or degassing).

The early atmosphere was formed almost entirely from volcanic emissions. There was no life on Earth at this stage, and the conditions were extremely hostile — the surface temperature was very high, and the atmosphere contained no free oxygen.