Hydrogen loss

During the Archean, there would have been a continuous production of hydrogen gas from the reaction of oxides in basalt rock with carbon dioxide and water. Water would have been split (see diagram) releasing hydrogen to the atmosphere, and locking the oxygen into the various carbonates of sodium, potassium, calcium, magnesium, and iron. Two important consequences would have arisen from this reaction. Firstly, the maintenance of an oxygen-free atmosphere and surface, providing a favourable environment for the accumulation of life chemicals. And secondly, the loss of hydrogen to space. Hydrogen atoms are extremely light, and the Earth’s gravitational field is not strong enough to prevent their escape.

How life has kept the planet moist

If hydrogen had continued to escape to space, then within a couple of billion years, Earth might well have lost all its water and become an arid, lifeless planet like Mars or Venus. Fortunately, however, life intervened. Firstly, by adding oxygen to the environment, as a by-product of photosynthesis (and of carbon burial). Some of this oxygen would undoubtedly have combined with free hydrogen in the reducing atmosphere of the Archean to form water, preventing its loss to space. Secondly, the free hydrogen produced on the ocean floor (see diagram) would have been used by certain bacteria to gain energy by making hydrogen sulphide, and the hydrogen thus would have been retained. The presence of life in the Archean saved our planet from a dry and dusty death. (see variation 19)