9.1.2 Earth's Early Atmosphere

Though the modern atmosphere has been stable for the past 200 million years, Earth's early atmosphere looked very different.

Composition of the Early Atmosphere:

• Early Theories:
  • During the first billion years of Earth's existence, its atmosphere likely resembled that of Venus or Mars today.
  • The Earth's surface was home to many volcanoes, which erupted frequently, releasing large amounts of gases into the atmosphere.

• Dominant Gases:
  • The early atmosphere was primarily composed of carbon dioxide (CO₂), with very little to no oxygen.
  • Other gases included water vapour (H₂O), methane (CH₄), and ammonia (NH₃).

• Nitrogen (N₂) was also released by volcanic activity and gradually built up in the atmosphere.
• Formation of Oceans:
  • As the Earth cooled over millions of years, the water vapour in the atmosphere began to condense, forming the oceans and seas that cover much of the Earth's surface today.