outgassing: one construct, many systems

In planetary geoscience, outgassing (degassing) is the release of volatile compounds held in a planet's interior (water, carbon dioxide, nitrogen) through volcanism and related activity, building up the oceans and atmosphere over geological time. Rubey's 1951 Geologic history of sea water framed the Earth's water and air as the accumulated product of such release from the solid planet rather than relics of its formation. The referent is the escape of a gas from a condensed phase as conditions allow it to come out of solution or trapping, the same physical construct that lets a diver's tissues off-gas or a material shed gas in vacuum, here on a planetary scale.[1]

Unit

The flux of volatiles released from the interior over geological time

Recovery means

Not applicable

Measured by

Estimated from volcanic gas fluxes, volatile budgets, and isotopic tracers of mantle degassing

In diving physiology, off-gassing is the elimination of inert gas that dissolved into the tissues at depth: as ambient pressure falls on ascent, the gas comes out of solution and is carried to the lungs and breathed out, provided the pressure drop is slow enough to avoid bubble formation. Bennett and Elliott's physiology and medicine of diving treats how different tissue compartments load and unload gas at their own rates, which is what decompression schedules are built around. It is the identical come-out-of-solution construct as a planet releasing volatiles or a material shedding adsorbed gas, realised in body tissue as pressure is reduced.[2]

Unit

The rate at which each tissue compartment unloads dissolved inert gas

Recovery means

Tissue gas tension returns toward equilibrium as the dissolved load is breathed off

Measured by

Modelled by compartment half-times and tracked against ascent rate and stop times

In vacuum technology and materials science, outgassing is the slow release of gas that was adsorbed on surfaces or dissolved in the bulk of a solid once that solid sits in an evacuated chamber, setting the ultimate pressure a vacuum system can reach and contaminating sensitive processes. O'Hanlon's A user's guide to vacuum technology treats outgassing rates and bake-out as central to achieving and holding high vacuum. The referent is the same escape of a trapped or dissolved gas from a condensed phase seen in a diver's tissues or a degassing planet, here driven by the pressure gradient into vacuum and measured as a surface gas-release rate.[3]

Unit

The gas-release rate per unit surface area into the evacuated space

Recovery means

Not applicable

Measured by

Quantified by outgassing-rate tests and the chamber's achievable base pressure, reduced by bake-out