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Why did Earth lose or fail to capture a primordial atmosphere of nebular gases?
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evolution of the atmosphere
A “best guess” reconstruction of the abundance of O2 in Earth's atmosphere as a function of time. The O2 abundance axis is logarithmic.
Earth likely failed to capture or retain a primordial atmosphere of nebular gases due to the early developmental phases of the Sun.1
There are two primary scientific explanations for this absence:
- Timing of Accretion: If the solar nebula's gases were dispersed by the pressure of light and particles from the young Sun before the inner planets had finished accreting, Earth would have been unable to capture a primordial atmosphere.1
- Solar-Wind Stripping: If Earth did accumulate a primordial atmosphere, it may have been completely lost due to the intense solar wind and extreme ultraviolet radiation emitted by the young Sun. This process, often described as atomic sandblasting, would have been particularly effective before Earth developed its protective geomagnetic field.12
Because Earth has a relatively weak gravitational field and experienced warm temperatures, it could not retain the most abundant light gases, such as hydrogen and helium, even if they had been captured. Consequently, the atmosphere that eventually developed on Earth is considered a secondary atmosphere.345