Midterm: Atmosphere/Hydrosphere Flashcards
Volatile sources
- Volatiles were present in the planetesimals (as hydrated minerals) and were thus accreted into the planets.
- The bulk of these volatiles released as Earth was heated by accretion and core formation, thus forming out atmosphere through outgassing.
- Comets may have added (and continue to add) volatiles as well.
- Outgassing on Earth is a continuing process as volcanism releases volatiles into the atmosphere, especially subduction zone volcanism where seafloor volatiles have been recycled into the mantle by plate tectonics.
- Water vapor makes up 70-95% of volcanic gases.
Methods of removal of volatiles
- Giant impacts
- Thermal/Hydrodynamic escape (it is easier to leave a small planet with lower escape velocity)
- Dissociation by UV radiation or solar particles (our magnetic field protects us from the latter)
Storage in rocks (more on this below)
What is the composition of the atmosphere of the Earth when it formed?
it’s atmosphere was ~95% CO2 and N2, similar to the atmospheres of Venus and Mars today. This has important consequences for planetary temperatures via the greenhouse effect: more CO2 means higher temperatures and thus a hot Venus, warm Earth, and clement Mars. This provides a potential solution to the faint young sun paradox.
What is the composition of the Earth’s atmosphere now?
The atmosphere of Earth is <0.01% of its total mass and is today composed of 78% N2, 21% O2, 1% Ar, and 0.035% CO2 (for “dry” air—H2O varies between 0-3% locally). Compare this to the atmospheres of Venus and Mars in terms of composition and global mass fraction.
