Abundance of Water
The abundance of water as the solvent of life is essential for life on the Earth. Ward and Brownlee in their discussion of the habitability of the Earth quote the abundance of water on the Earth as 0.1% and that of carbon as 0.05%. Later they quote the water abundance by weight as about half a percent, so this may give the range of uncertainty in the estimates. They contrast this with the concentrations in carbonaceous meteorites which contain up to 20% water and 4% carbon. Even though the water abundance seems low, it is actually quite large compared to the other rocky planets and the source of all the water on the Earth is still somewhat uncertain. The high abundance of water in the meterorites and in comets leads to the hypothesis that the water came from intense early bombardment of the Earth by such bodies. By contrast, the studies of moon minerals from the Apollo program revealed the minerals of the moon to be remarkably dry, with little or none of the hydration that is common in similar Earth minerals (Ward & Brownlee, Ch 11).
Ward and Brownlee