Hydrogen loss from earth

In either case, the oxidation of the planet is the consequence of the photodissociation of water vapor and loss of hydrogen to space. In order to fractionate the rare gases by entrainment in the hydrogen streaming from Earth, this process must have occurred almost instantaneously in the early history of the Earth. Therefore, it is reasonable to assume that both water and rare gases were at the Earth s surface virtually at the time of formation of the Earth. 

Although little water manages to pass through the cold trap, there are other sources of hydrogen in the upper air. As mentioned above, methane emissions from the surface mix upwards from the surface, as methane has no cold trap, and in the upper air photolysis leads eventually to release of H. In addition, there is a small emission of H2 from the surface, some of which will reach the upper part of the atmosphere however. Earth also sweeps up H and H2 from space. Over time, net hydrogen loss must have been limited we have kept the oceans. 

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. 

Up to 80-100 km from the Earth s surface is the ionosphere, a region of highly rarefied and ionized gas molecules. The exosphere, the outermost belt of the gas shield, might extend as far as 1800 km. The losses of the lightest gases, hydrogen and helium, into space from the Earth s atmosphere occur in the exosphere. 

It can be seen from Table 3 that the dissipation of noble gases was particularly intense. This is reasonable, since these gases did not react with the solid or liquid materials forming the planet Earth. On the other hand the loss in the case of hydrogen was relatively small, a significant portion of this element remained in a condensing compound (water). 

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