Earth’s Early Atmosphere

As Earth is around 4.6 billion years old, the evidence for the Earth’s early atmosphere is limited.

One theory suggests that Earth’s early atmosphere was formed through the release of gases from the planet’s interior, as a result of intense volcanic activity.

During the first billion years, the Earth was very dry and there was intense volcanic activity. The volcanoes released gases that formed the atmosphere, which include:

  • Carbon dioxide
  • Water vapour
  • Nitrogen
  • Small amounts of methane and ammonia

The Earth’s early atmosphere was very similar to the atmospheres of Mars and Venus today, as it was mostly made up of carbon dioxide, with little to no oxygen.

As the Earth cooled, water vapour condensed into liquid water, forming the oceans. A lot of carbon dioxide from the atmosphere dissolved in the oceans, forming carbon precipitates, which eventually formed sediments. This resulted in carbon being locked away in sediments.

Eventually, photosynthetic algae began to appear, and over the next billion years, many green plants evolved. The process of photosynthesis uses up carbon dioxide and forms oxygen, which you can see in the equation below:

Carbon DioxideWater → Glucose + Oxygen

6CO2 + H2O → C6H12O6 + 6O2

Gradually, the amount of carbon dioxide in the atmosphere declined, and the amount of oxygen increased. This allowed more complex organisms to evolve.