Evolution of the Atmosphere
- Theories on the development of Earth’s atmosphere have altered and developed over time as instrumental analysis has improved
- It is difficult to gather evidence about the early atmosphere because it happened 4.6 billion years ago
- The surface of the early Earth was molten for millions of years during which time there was no atmosphere surrounding the planet
- Eventually, cooling began to take effect and allow for molten materials to slowly solidify forming land masses
- Volcanoes formed on the land masses
- One theory of how the early atmosphere formed suggests that the volcanoes released gases from the Earth’s interior through violent eruptions
- These eruptions released large amounts of carbon dioxide and water vapour, as well as nitrogen, hydrogen, and other gases which may have included small proportions of ammonia and methane
- Earth’s gravity prevented the gases from escaping into outer space and they formed the early atmosphere
- Analysis of the minerals in the Earth's crust enables scientists to deduce the gases present billions of years ago that helped form those minerals
- It is thought that the atmosphere at that moment in Earth’s history was similar to that of Venus or Mars today which consist mainly of CO2
- The early atmosphere, therefore, is thought to have contained mainly CO2 and water vapour
- There was little or no oxygen present
Volcanoes spewed out water, carbon dioxide and other gases from the Earth’s interior
- While the surface of the Earth was still very hot the large quantities of water vapour remained in the gaseous state
- When conditions cooled sufficiently, the water vapour later condensed and fell to the surface of the Earth, forming the oceans
- Carbon dioxide is a water soluble gas (it is the gas used in fizzy drinks) and dissolves readily
- When the water vapour condensed large amounts of CO2 dissolved in the oceans
- Carbonate substances were precipitated during this process which later formed sediments
- These processes reduced the amount of carbon dioxide in the atmosphere
Exam Tip
For this topic you should be able to describe this theory of how the atmosphere and oceans came about. You may be given information on alternative theories which you could be asked to evaluate.
