69. Evolution of the Atmosphere

1. The Early Atmosphere (First Billion Years)

• Volcanic Activity: Intense volcanic activity released large amounts of carbon dioxide (CO2), water vapor, and nitrogen, along with smaller amounts of methane and ammonia.

• Composition: The early atmosphere was mostly CO2, similar to Mars and Venus today. There was little to no oxygen.

• Formation of Oceans: As the Earth cooled, water vapor condensed into liquid water to form the oceans. This allowed a significant amount of CO2 to dissolve in the water.

2. Reduction of Carbon Dioxide

• Dissolution and Sedimentation: CO2 dissolved in the oceans formed carbonate precipitates and eventually became sediments on the seabed.

• Photosynthesis: About 2.7 billion years ago, algae appeared, followed by green plants. Through photosynthesis, these organisms absorbed CO2 and released oxygen.

• Carbon Sequestration: When these organisms died, they were buried under layers of sediment. Over millions of years, they were compressed into:

  • Crude oil and natural gas: Formed from dead plankton.

  • Coal: Formed from thick deposits of dead plant material.

  • Limestone: Formed from the calcium carbonate in the shells and skeletons of marine organisms.

3. Increase in Oxygen

• Life Evolution: As algae and plants multiplied, oxygen levels built up in the atmosphere.

• Complex Life: This increase in oxygen eventually reached levels high enough to allow more complex life, such as animals, to evolve.

4. Modern Atmosphere Composition

Today, the atmosphere has remained stable for about 200 million years with approximately:

• 80% Nitrogen

• 20% Oxygen

• < 1% Other gases (including carbon dioxide, water vapor, and noble gases).

Summary of Changes