Venus hydrogen loss

Hydrogen isotopes have also been fractionated during planetary geologic processes. Compared to the Earth, Venus and Mars have significantly elevated D/H ratios (5D = 125 000 permil and 4000 permil, respectively). These fractionations are thought to result from preferential loss of H relative to D from the atmospheres of these planets (Robert el al., 2000) atmospheric escape of hydrogen from the Earth was apparently not important. 

The oxidation of Fe " "-bearing minerals in basalt (and other volcanic rocks on Venus surface) is potentially very important for water loss via oxidation of the surface and hydrogen escape to space. The overall process is schematically represented by... 

Earth is currently balanced on the hquid island east of water s triple point, but this balancing act was difficult to maintain. Any planet left out in the vacuum of space changes in temperature and pressure over time. Air pressure leaked away as hydrogen left the Earth and carbon dioxide was packed into limestone. Gravity and sunlight helped compensate for the loss, but stability can be elusive—just ask Venus and Mars. 

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